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Large Hadron ColliderExperiments, Technology, Theory andFuture of the world's largest andhighest-energy particle accelerator

ContentsArticlesOverview 1

CERN 1Large Hadron Collider 11

Experiments 23

List of LHC experiments 23ALICE 26ATLAS 29CMS 38LHCb 46LHCf 49FP420 50TOTEM 51

Technology 53

Beetle ASIC 53LHC Computing Grid 54LHC@home 55Proton Synchrotron Booster 56VELO 56

Theory 57

Standard Model 57Particle physics 70Superpartner 74Supersymmetry 75Higgs boson 82

Safety 90

Safety of particle collisions at the Large Hadron Collider 90Micro black hole 99Strangelet 104

Future 109

Super Large Hadron Collider 109Very Large Hadron Collider 111

ReferencesArticle Sources and Contributors 112Image Sources, Licenses and Contributors 115

Article LicensesLicense 118

1

Overview

CERN

European Organizationfor Nuclear Research

Organisation Européennepour la Recherche Nucléaire

Member statesFormation 29 September 1954[1]

Headquarters Geneva, Switzerland

Membership 20 member states and 8 observers

Director General Rolf-Dieter Heuer

Website http:/ / www. cern. ch/

CERN 2

The 12 founding member states of CERN in 1954a[›] (map borders from 1989)

54 years after its foundation, membership toCERN increased to 20 states, 18 of which are also

EU members as of 2010

The European Organization for Nuclear Research (French: Organisation Européenne pour la RechercheNucléaire), known as CERN (see History), pronounced /ˈsərn/ (French pronunciation: [sɛʁn]), is the world's largestparticle physics laboratory, situated in the Northwest suburbs of Geneva on the Franco–Swiss border (46°14′3″N6°3′19″E), established in 1954. The organization has twenty European member states, and is the workplace ofapproximately 2,600 full-time employees, as well as some 7,931 scientists and engineers representing 580universities and research facilities and 80 nationalities.CERN's main function is to provide the particle accelerators and other infrastructure needed for high-energy physicsresearch. Numerous experiments have been constructed at CERN by international collaborations to make use ofthem. It is also the birthplace of the World Wide Web. The main site at Meyrin also has a large computer centrecontaining very powerful data-processing facilities primarily for experimental data analysis and, because of the needto make them available to researchers elsewhere, has historically been a major wide area networking hub.The CERN sites, as an international facility, are officially under neither Swiss nor French jurisdiction. Memberstates' contributions to CERN for the year 2008 totalled CHF 1 billion (approximately € 664 million).

CERN 3

HistoryThe convention establishing CERN was ratified on 29 September 1954 by 12 countries in Western Europe.a[›][1] Theacronym CERN originally stood, in French, for Conseil Européen pour la Recherche Nucléaire (European Councilfor Nuclear Research), which was a provisional council for setting up the laboratory, established by 11 Europeangovernments in 1952. The acronym was retained for the new laboratory after the provisional council was dissolved,even though the name changed to the current Organisation Européenne pour la Recherche Nucléaire (EuropeanOrganization for Nuclear Research) in 1954.[2] According to Lew Kowarski, a former director of CERN, when thename was changed the acronym could have become the awkward OERN, and Heisenberg said that the acronymcould "still be CERN even if the name is [not]".Soon after its establishment the work at the laboratory went beyond the study of the atomic nucleus intohigher-energy physics, which is mainly concerned with the study of interactions between particles. Therefore thelaboratory operated by CERN is commonly referred to as the European laboratory for particle physics(Laboratoire européen pour la physique des particules) which better describes the research being performed atCERN.

Scientific achievementsSeveral important achievements in particle physics have been made during experiments at CERN. They include:• 1973: The discovery of neutral currents in the Gargamelle bubble chamber.[3]

• 1983: The discovery of W and Z bosons in the UA1 and UA2 experiments.[4]

• 1989: The determination of the number of light neutrino families at the Large Electron–Positron Collider (LEP)operating on the Z boson peak.

• 1995: The first creation of antihydrogen atoms in the PS210 experiment.[5]

• 1999: The discovery of direct CP-violation in the NA48 experiment.[6]

• 2010: The isolation of 38 atoms of anti-hydrogen [7]

The 1984 Nobel Prize in physics was awarded to Carlo Rubbia and Simon van der Meer for the developments thatled to the discoveries of the W and Z bosons. The 1992 Nobel Prize in physics was awarded to CERN staffresearcher Georges Charpak "for his invention and development of particle detectors, in particular the multiwireproportional chamber."

Computer science

This NeXT Computer used by British scientist SirTim Berners-Lee at CERN became the first Web

server.

The World Wide Web began as a CERN project called ENQUIRE,initiated by Tim Berners-Lee in 1989 and Robert Cailliau in 1990.[8]

Berners-Lee and Cailliau were jointly honored by the Association forComputing Machinery in 1995 for their contributions to thedevelopment of the World Wide Web.

Based on the concept of hypertext, the project was aimed at facilitatingsharing information among researchers. The first website went on-linein 1991. On 30 April 1993, CERN announced that the World WideWeb would be free to anyone. A copy[9] of the original first webpage,created by Berners-Lee, is still published on the World Wide WebConsortium's website as a historical document.

CERN 4

This Cisco Systems router at CERN was probablyone of the first IP routers deployed in Europe.

Prior to the Web's development, CERN had been a pioneer in theintroduction of Internet technology, beginning in the early 1980s. Ashort history of this period can be found at CERN.ch.[10]

More recently, CERN has become a centre for the development of Gridcomputing, hosting among others the Enabling Grids for E-sciencE(EGEE) and LHC Computing Grid projects. It also hosts the CERNInternet Exchange Point (CIXP), one of the two main InternetExchange Points in Switzerland. CERN's computer network isconnected to JANET (formerly UKERNA), the research and educationnetwork, JANET aids CERN to disperse large data over a network gridfor closer analysis.

Particle accelerators

Current complex

Map of the Large Hadron Collider together withthe Super Proton Synchrotron at CERN

CERN operates a network of six accelerators and a decelerator. Eachmachine in the chain increases the energy of particle beams beforedelivering them to experiments or to the next more powerfulaccelerator. Currently active machines are:• Two linear accelerators generate low energy particles. Linac2

accelerates protons to 50 MeV for injection into the ProtonSynchrotron Booster (PSB), and Linac3 provides heavy ions at4.2 MeV/u for injection into the Low Energy Ion Ring (LEIR).[11]

• The Proton Synchrotron Booster increases the energy of particlesgenerated by the proton linear accelerator before they aretransferred to the other accelerators.

• The Low Energy Ion Ring (LEIR) accelerates the ions from the ionlinear accelerator, before transferring them to the ProtonSynchrotron (PS). This accelerator was commissioned in 2005, afterhaving been reconfigured from the previous Low Energy Antiproton Ring (LEAR).

• The 28 GeV Proton Synchrotron (PS), built in 1959 and still operating as a feeder to the more powerful SPS.• The Super Proton Synchrotron (SPS), a circular accelerator with a diameter of 2 kilometres built in a tunnel,

which started operation in 1976. It was designed to deliver an energy of 300 GeV and was gradually upgraded to450 GeV. As well as having its own beamlines for fixed-target experiments (currently COMPASS and NA62), ithas been operated as a proton–antiproton collider (the SppS collider), and for accelerating high energy electronsand positrons which were injected into the Large Electron–Positron Collider (LEP). Since 2008, it has been usedto inject protons and heavy ions into the Large Hadron Collider (LHC).

• The On-Line Isotope Mass Separator (ISOLDE), which is used to study unstable nuclei. The radioactive ions areproduced by the impact of protons at an energy of 1.0–1.4 GeV from the Proton Synchrotron Booster. It was firstcommissioned in 1967 and was rebuilt with major upgrades in 1974 and 1992.

• REX-ISOLDE increases the charge states of ions coming from the ISOLDE targets, and accelerates them to amaximum energy of 3 MeV/u.

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• The Antiproton Decelerator (AD), which reduces the velocity of antiprotons to about 10% of the speed of light forresearch into antimatter.

• The Compact Linear Collider Test Facility, which studies feasibility issues for the future normal conducting linearcollider project.

The Large Hadron Collider

Construction of the CMS detector forLHC at CERN

Most of the activities at CERN are currently directed towards building a newcollider, the Large Hadron Collider (LHC) and the experiments for it. The LHCrepresents a large-scale, worldwide scientific cooperation project.

The LHC tunnel is located 100 metres underground, in the region between theGeneva airport and the nearby Jura mountains. It uses the 27 km circumferencecircular tunnel previously occupied by LEP which was closed down inNovember 2000. CERN's existing PS/SPS accelerator complexes will be used topre-accelerate protons which will then be injected into the LHC.

Seven experiments (CMS, ATLAS, LHCb, MoEDAL[12] TOTEM, LHC-forwardand ALICE) will run on the collider; each of them will study particle collisionsfrom a different point of view, and with different technologies. Construction forthese experiments required an extraordinary engineering effort. Just as anexample, a special crane had to be rented from Belgium in order to lower piecesof the CMS detector into its underground cavern, since each piece weighednearly 2,000 tons. The first of the approximately 5,000 magnets necessary for construction was lowered down aspecial shaft at 13:00 GMT on 7 March 2005.

This accelerator will generate vast quantities of computer data, which CERN will stream to laboratories around theworld for distributed processing (making use of a specialised grid infrastructure, the LHC Computing Grid). In April2005, a trial successfully streamed 600 MB/s to seven different sites across the world. If all the data generated by theLHC is to be analysed, then scientists must achieve 1,800 MB/s before 2008.The initial particle beams were injected into the LHC August 2008.[13] The first attempt to circulate a beam throughthe entire LHC was at 8:28 GMT on 10 September 2008,[14] but the system went wrong because of a faulty magnetconnection, and it was stopped for repairs on 19 September 2008.The LHC resumed its operation on Friday the 20th of November 2009 by successfully circulating two beams, eachwith an energy of 3.5 trillion electron volts. The challenge that the engineers then faced was to try and line up thetwo beams so that they smashed into each other. This is like "firing two needles across the Atlantic and getting themto hit each other" according to the LHC's main engineer Steve Myers, director for accelerators and technology at theSwiss laboratory.At 1200 BST on Tuesday the 30th of March 2010 the LHC successfully smashed two proton particle beamstravelling with 3.5 TeV (trillion electron volts) of energy, resulting in a 7 TeV event. However this is just the start ofa long road toward the expected discovery of the Higgs boson. This is mainly because the amount of data producedis so huge it could take up to 24 months to completely analyse it all. At the end of the 7 TeV experimental period, theLHC will be shut down for maintenance for up to a year, with the main purpose of this shut down being to strengthenthe huge magnets inside the accelerator. When it re-opens, it will attempt to create 14 TeV events.

CERN 6

Decommissioned accelerators• The original linear accelerator (LINAC 1).• The 600 MeV Synchrocyclotron (SC) which started operation in 1957 and was shut down in 1991.• The Intersecting Storage Rings (ISR), an early collider built from 1966 to 1971 and operated until 1984.• The Large Electron–Positron Collider (LEP), which operated from 1989 to 2000 and was the largest machine of

its kind, housed in a 27 km-long circular tunnel which now houses the Large Hadron Collider.• The Low Energy Antiproton Ring (LEAR), commissioned in 1982, which assembled the first pieces of true

antimatter, in 1995, consisting of nine atoms of antihydrogen. It was closed in 1996, and superseded by theAntiproton Decelerator.

Sites

CERN's main site, as seen from Switzerland looking towards France.

Interior of office building 40 at theMeyrin site. Building 40 hosts many

offices for scientists working for CMSand Atlas.

The smaller accelerators are located on the mainMeyrin site (also known as the West Area), which wasoriginally built in Switzerland alongside the Frenchborder, but has been extended to span the border since1965. The French side is under Swiss jurisdiction andso there is no obvious border within the site, apart froma line of marker stones. There are six entrances to theMeyrin site:

• A, in Switzerland. Open for all CERN personnel atspecific times.

• B, in Switzerland. Open for all CERN personnel atall times. Often referred to as the main entrance.

• C, in Switzerland. Open for all CERN personnel atspecific times.

• D, in Switzerland. Open for goods reception atspecific times.

• E, in France. Open for French-resident CERNpersonnel at specific times. Controlled by customspersonnel. Named "Porte Charles de Gaulle" inrecognition of his role in the creation of theCERN.[15]

• Tunnel entrance, in France. Open for equipmenttransfer to and from CERN sites in France bypersonnel with a specific permit. This is the onlypermitted route for such transfers. Under the CERNtreaty, no taxes are payable when such transfers aremade. Controlled by customs personnel.

The SPS and LEP/LHC tunnels are locatedunderground almost entirely outside the main site, and are mostly buried under French farmland and invisible fromthe surface. However they have surface sites at various points around them, either as the location of buildingsassociated with experiments or other facilities needed to operate the colliders such as cryogenic plants and accessshafts. The experiments themselves are located at the same underground level as the tunnels at these sites.Three of these experimental sites are in France, with ATLAS in Switzerland, although some of the ancillary cryogenic and access sites are in Switzerland. The largest of the experimental sites is the Prévessin site, also known

CERN 7

as the North Area, which is the target station for non-collider experiments on the SPS accelerator. Other sites are theones which were used for the UA1, UA2 and the LEP experiments (the latter which will be used for LHCexperiments).Outside of the LEP and LHC experiments, most are officially named and numbered after the site where they werelocated. For example, NA32 was an experiment looking at the production of charmed particles and located at thePrévessin (North Area) site while WA22 used the Big European Bubble Chamber (BEBC) at the Meyrin (WestArea) site to examine neutrino interactions. The UA1 and UA2 experiments were considered to be in theUnderground Area, i.e. situated underground at sites on the SPS accelerator.

Financing (Budget 2009)

Member state Contribution Mil. CHF Mil. EUR

 Germany 19.88 % 218.6 144.0

 France 15.34 % 168.7 111.2

 United Kingdom 14.70 % 161.6 106.5

 Italy 11.51 % 126.5 83.4

 Spain 8.52 % 93.7 61.8

 Netherlands 4.79 % 52.7 34.7

 Switzerland 3.01 % 33.1 21.8

 Poland 2.85 % 31.4 20.7

 Belgium 2.77 % 30.4 20.1

 Sweden 2.76 % 30.4 20.0

 Norway 2.53 % 27.8 18.3

 Austria 2.24 % 24.7 16.3

 Greece 1.96 % 20.5 13.5

 Denmark 1.76 % 19.4 12.8

 Finland 1.55 % 17.0 11.2

 Czech Republic 1.15 % 12.7 8.4

 Portugal 1.14 % 12.5 8.2

 Hungary 0.78 % 8.6 5.6

 Slovakia 0.54 % 5.9 3.9

 Bulgaria 0.22 % 2.4 1.6

Exchange rates: 1 CHF = 0,659 EUR (May 25, 2009)

CERN 8

Member states

Member states of CERN as of 2008   Founding members  Memberswho joined CERN later

Animated map showing changes in CERN membership from 1954until 1999 (borders as of 1989 and 2008)

CERN members (in blue) and observers (in red: USA, Israel, Turkey,Japan, India, and Russia) as of 2008

The original twelve (12) CERN signatories from 1954were:

•  Belgium•  Denmark•  France•  Germany (at first only West Germany)•  Greece•  Italy•  Netherlands•  Norway•  Sweden•  Switzerland•  United Kingdom•  Yugoslavia (later withdrawn)All founding members have so far (as of 2008)remained in the CERN organisation, except Yugoslaviawhich left in 1961 and never re-joined.

Since its foundation, CERN regularly accepted newmembers. All new members have remained in theorganisation continuously since their acceptance,except Spain which joined in 1961, withdrew eightyears later, and joined anew in 1983. CERN'smembership history is as follows:

•  Austria joined in 1959, bringing the totalnumber of members to 13.

•  Yugoslavia left in 1961 (12 members)•  Spain joined in 1961 (thus increasing the

number of member states to 13 again), left in 1969(12 members), rejoined in 1983 (13 members)

•  Portugal joined in 1985 (14 member states)•  Finland joined in 1991•  Poland joined in 1991 (together with Finland

bringing the number of participating member statesto 16)

•  Hungary joined in 1992 (17 members)•  Czech Republic joined in 1993•  Slovakia joined in 1993 (together with Czech

Republic increasing the total members to 19)•  Bulgaria joined in 1999 (20 member states)There are currently twenty (20) member countries, 18of which are also European Union member states.

CERN 9

CERN: where the Web was born[16]

•  Romania became a candidate for accession to CERN in 2010and will become the 21st member country in 2015[17]

•  Serbia became a candidate for accession to CERN in December2010. Accession talks are expected to last 3 years. [18]

Six (6) additional countries have observer status:[19]

•  Turkey – since 1961•  Israel – since 1991•  Russia – since 1993•  Japan – since 1995•  United States – since 1997•  India – since 2002Also observers are the following international organizations:• UNESCO – since 1954• European Commission – since 1985Non-Member States (with dates of Co-operation Agreements) currently involved in CERN programmes are:•  Algeria•  Argentina – 11 March 1992•  Armenia – 25 March 1994•  Australia – 1 November 1991•  Azerbaijan – 3 December 1997•  Belarus – 28 June 1994•  Brazil – 19 February 1990 & October 2006•  Canada – 11 October 1996•  Chile – 10 October 1991•  People's Republic of China – 12 July 1991, 14 August 1997 & 17 February 2004•  Colombia – 15 May 1993•  Croatia – 18 July 1991•  Cuba•  Cyprus – 14 February 2006•  Estonia – 23 April 1996•  Georgia – 11 October 1996•  Iceland – 11 September 1996•  Iran – 5 July 2001•  Ireland•  Lithuania – 9 November 2004•  Macedonia – 27 April 2009[20]

•  Mexico – 20 February 1998•  Montenegro – 12 October 1990•  Morocco – 14 April 1997•  New Zealand – 4 December 2003•  Pakistan – 1 November 1994. The possibility of Pakistan becoming an Observer State has been raised on

various occasions.•  Peru – 23 February 1993•  Romania – 1 October 1991. Since 12 December 2008 it has the Status of Candidate for Accession to

Membership.

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•  Serbia – 8 June 2001. In 2008 it applied for accession to CERN as a Member State.[21] . Since 19 December2010 it has the Status of Candidate for Accession to Membership.[22]

•  Slovenia – 7 January 1991•  South Africa – 4 July 1992•  South Korea – 25 October 2006. It might become a candidate for CERN Observer Status in a few years.•  Republic of China (Taiwan)•  Thailand•  Ukraine – 2 April 1993•  Vietnam

Public exhibits

The Globe of Science and Innovation at CERN

Facilities at CERN open to the public include:• The Globe of Science and Innovation, which opened in

late 2005 and is used four times a week for specialexhibits.

• The Microcosm museum on particle physics and CERNhistory.

In popular culture

• CERN is mentioned in several works of fiction andscience fiction such as Robert J. Sawyer's Flashforwardand Dan Brown's Angels & Demons in which antimatterfigures prominently.

• CERN's Large Hadron Collider is the subject of a (scientifically accurate) rap video starring Katherine McAlpinewith some of the facility's staff.[23] [24]

• CERN is also referenced in several episodes of The Big Bang Theory and there is a Season 3 episode in which theLarge Hadron Collider features prominently called The Large Hadron Collision.

References[1] "CERN.ch" (http:/ / public. web. cern. ch/ public/ en/ About/ History54-en. html). Public.web.cern.ch. . Retrieved 2010-11-20.[2] The CERN Name (http:/ / public. web. cern. ch/ Public/ Content/ Chapters/ AboutCERN/ WhatIsCERN/ CERNName/ CERNName-en. html),

on the CERN website.[3] "CERN.ch" (http:/ / public. web. cern. ch/ public/ en/ About/ History73-en. html). Public.web.cern.ch. . Retrieved 2010-11-20.[4] "CERN.ch La" (http:/ / public. web. cern. ch/ public/ en/ About/ History83-en. html). Public.web.cern.ch. . Retrieved 2010-11-20.[5] "CERN.ch" (http:/ / public. web. cern. ch/ public/ en/ About/ History95-en. html). Public.web.cern.ch. . Retrieved 2010-11-20.[6] "V. Fanti et al., Phys. Lett. B465 (1999) 335 (hep-ex/9909022)0" (http:/ / arxiv. org/ abs/ hep-ex/ 9909022v1). Arxiv.org. 1999-09-13. .

Retrieved 2010-11-20.[7] "Antihydrogen isolation" (http:/ / edition. cnn. com/ 2010/ WORLD/ europe/ 11/ 18/ switzerland. cern. antimatter/ ?hpt=Mid). CNN. .[8] "CERN.ch" (http:/ / public. web. cern. ch/ Public/ en/ About/ WebStory-en. html). Public.web.cern.ch. . Retrieved 2010-11-20.[9] "W3.org" (http:/ / www. w3. org/ History/ 19921103-hypertext/ hypertext/ WWW/ TheProject. html). W3.org. . Retrieved 2010-11-20.[10] "CERN.ch" (http:/ / www. cern. ch/ ben/ TCPHIST. html). CERN.ch. . Retrieved 2010-11-20.[11] "CERN Website – LINAC" (http:/ / linac2. home. cern. ch/ linac2/ default. htm). Linac2.home.cern.ch. . Retrieved 2010-11-20.[12] CERN Courier, "MoEDAL becomes the LHC's magnificent seventh" (http:/ / cerncourier. com/ cws/ article/ cern/ 42329), May 5th 2010[13] Overbye, Dennis (29 July 2008). " Let the Proton Smashing Begin. (The Rap Is Already Written.) (http:/ / www. nytimes. com/ 2008/ 07/

29/ science/ 29cernrap. html)". The New York Times.[14] "CERN press release, 7 August 2008" (http:/ / press. web. cern. ch/ press/ PressReleases/ Releases2008/ PR06. 08E. html).

Press.web.cern.ch. 2008-08-07. . Retrieved 2010-11-20.[15] "Red Carpet for CERN's 50th" (http:/ / bulletin. cern. ch/ eng/ articles. php?bullno=45/ 2004& base=art). CERN bulletin. November 2004. .[16] Plaque #2196 on Open Plaques (http:/ / openplaques. org/ plaques/ 2196).

CERN 11

[17] "CERN.ch" (http:/ / public. web. cern. ch/ public/ ). Public.web.cern.ch. doi:10.1038/nature09610. . Retrieved 2010-11-20.[18] (http:/ / www. blic. rs/ Vesti/ Drustvo/ 224590/ Odobrena-kandidatura-Srbije-za-clanstvo-u-CERNu)[19] "ISAAR relationship data at CERN library" (http:/ / library. web. cern. ch/ library/ Archives/ archnet/ isaarcern. html). . Retrieved

2009-12-14.[20] "''Macedonia joins CERN (SUP)''" (http:/ / www. mia. com. mk/ default. aspx?mId=1& vId=64153836& lId=2& title=MACEDONIA+ -+

INTERNAL+ AFFAIRS+ ). Mia.com.mk. . Retrieved 2010-11-20.[21] "Djelic to meet CERN Director General" (http:/ / www. emportal. rs/ en/ news/ serbia/ 87520. html). Emportal.rs. . Retrieved 2010-11-20.[22] (http:/ / www. blic. rs/ Vesti/ Drustvo/ 224590/ Odobrena-kandidatura-Srbije-za-clanstvo-u-CERNu)[23] "Youtube.com" (http:/ / www. youtube. com/ watch?v=j50ZssEojtM). Youtube.com. . Retrieved 2010-11-20.[24] "Large Hadron Collider Rap Video Is a Hit" (http:/ / news. nationalgeographic. com/ news/ 2008/ 09/ 080910-odd-particl-AP. html),

National Geographic News. September 10, 2008. Retrieved August 13, 2010.

External links• Official website (http:/ / http:/ / www. cern. ch)• CERN at 50 (http:/ / www. economist. com/ science/ PrinterFriendly. cfm?Story_ID=2535917)• CERN Courier – International journal of high-energy physics (http:/ / cerncourier. com)• CERN chronology (http:/ / library. cern. ch/ archives/ chrono/ chrono_2002_cern. php)Geographical coordinates: 46°14′03″N 6°03′10″E

Large Hadron ColliderGeographical coordinates: 46°14′N 06°03′E

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton Synchrotron

SPS Super Proton Synchrotron

Large Hadron Collider 12

Intersecting Storage Rings CERN, 1971–1984

Super Proton Synchrotron CERN, 1981–1984

ISABELLE BNL, cancelled in 1983

Tevatron Fermilab, 1987–present

Relativistic Heavy Ion Collider BNL, 2000–present

Superconducting Super Collider Cancelled in 1993

Large Hadron Collider CERN, 2009–present

Super Large Hadron Collider Proposed, CERN, 2019–

Very Large Hadron Collider Theoretical

The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It is expected thatit will address some of the most fundamental questions of physics, advancing humanity's understanding of thedeepest laws of nature.The LHC lies in a tunnel 27 kilometres (17 mi) in circumference, as much as 175 metres (574 ft) beneath theFranco-Swiss border near Geneva, Switzerland. This synchrotron is designed to collide opposing particle beams ofeither protons at an energy of 7 teraelectronvolts (1.12 microjoules) per particle, or lead nuclei at an energy of574 TeV (92.0 µJ) per nucleus.[1] [2] The term hadron refers to particles composed of quarks.The Large Hadron Collider was built by the European Organization for Nuclear Research (CERN) with the intentionof testing various predictions of high-energy physics, including the existence of the hypothesized Higgs boson[3] andof the large family of new particles predicted by supersymmetry.[4] It is funded by and built in collaboration withover 10,000 scientists and engineers from over 100 countries as well as hundreds of universities and laboratories.[5]

On 10 September 2008, the proton beams were successfully circulated in the main ring of the LHC for the firsttime,[6] but 9 days later operations were halted due to a serious fault.[7] On 20 November 2009 they weresuccessfully circulated again,[8] with the first proton–proton collisions being recorded 3 days later at the injectionenergy of 450 GeV per beam.[9] After the 2009 winter shutdown, the LHC was restarted and the beam was rampedup to 3.5 TeV per beam,[10] half its designed energy.[11] On 30 March 2010, the first planned collisions took placebetween two 3.5 TeV beams, which set a new world record for the highest-energy man-made particle collisions.[12]

Purpose

A simulated event in the CMS detector, featuringthe appearance of the Higgs boson

Physicists hope that the LHC will help answer many of the mostfundamental questions in physics: questions concerning the basic lawsgoverning the interactions and forces among the elementary objects,the deep structure of space and time, especially regarding theintersection of quantum mechanics and general relativity, wherecurrent theories and knowledge are unclear or break down altogether.These issues include, at least:[13]

• Is the Higgs mechanism for generating elementary particle massesvia electroweak symmetry breaking indeed realised in nature?[14] Itis anticipated that the collider will either demonstrate or rule out theexistence of the elusive Higgs boson(s), completing (or refuting) theStandard Model.[15] [16] [17]

• Is supersymmetry, an extension of the Standard Model and Poincarésymmetry, realised in nature, implying that all known particles have supersymmetric partners?[18] [19] [20]

Large Hadron Collider 13

• Are there extra dimensions,[21] as predicted by various models inspired by string theory, and can we detectthem?[22]

• What is the nature of the Dark Matter which appears to account for 23% of the energy density of the Universe?Other questions are:• Are electromagnetism, the strong nuclear force and the weak nuclear force just different manifestations of a single

unified force, as predicted by various Grand Unification Theories?• Why is gravity so many orders of magnitude weaker than the other three fundamental forces? See also Hierarchy

problem.• Are there additional sources of quark flavour mixing, beyond those already predicted within the Standard Model?• Why are there apparent violations of the symmetry between matter and antimatter? See also CP violation.• What was the nature of the quark-gluon plasma in the early universe? This will be investigated by heavy ion

collisions in ALICE.

Design

A Feynman diagram of one way the Higgs bosonmay be produced at the LHC. Here, two quarkseach emit a W or Z boson, which combine to

make a neutral Higgs.

Map of the Large Hadron Collider at CERN

The LHC is the world's largest and highest-energy particleaccelerator.[1] [23] The collider is contained in a circular tunnel, with acircumference of 27 kilometres (17 mi), at a depth ranging from 50 to175 metres (160 to 574 ft) underground.

The 3.8-metre (12 ft) wide concrete-lined tunnel, constructed between1983 and 1988, was formerly used to house the LargeElectron–Positron Collider.[24] It crosses the border betweenSwitzerland and France at four points, with most of it in France.Surface buildings hold ancillary equipment such as compressors,ventilation equipment, control electronics and refrigeration plants.

The collider tunnel contains two adjacent parallel beam pipes thatintersect at four points, each containing a proton beam, which travel inopposite directions around the ring. Some 1,232 dipole magnets keepthe beams on their circular path, while an additional 392 quadrupolemagnets are used to keep the beams focused, in order to maximize thechances of interaction between the particles in the four intersectionpoints, where the two beams will cross. In total, over 1,600superconducting magnets are installed, with most weighing over 27tonnes. Approximately 96 tonnes of liquid helium is needed to keep themagnets at their operating temperature of 1.9 K (−271.25 °C), makingthe LHC the largest cryogenic facility in the world at liquid heliumtemperature.

Large Hadron Collider 14

Superconducting quadrupole electromagnets areused to direct the beams to four intersection

points, where interactions between acceleratedprotons will take place.

Once or twice a day, as the protons are accelerated from 450 GeV to7 TeV, the field of the superconducting dipole magnets will beincreased from 0.54 to 8.3 teslas (T). The protons will each have anenergy of 7 TeV, giving a total collision energy of 14 TeV. At thisenergy the protons have a Lorentz factor of about 7,500 and move atabout 0.999999991 c, or about 3 metres per second slower than thespeed of light (c).[25] It will take less than 90 microseconds (μs) for aproton to travel once around the main ring – a speed of about 11,000revolutions per second. Rather than continuous beams, the protons willbe bunched together, into 2,808 bunches, so that interactions betweenthe two beams will take place at discrete intervals never shorter than 25nanoseconds (ns) apart. However it will be operated with fewerbunches when it is first commissioned, giving it a bunch crossing

interval of 75 ns.[26] The design luminosity of the LHC is 1034 cm−2s−1, providing a bunch collision rate of40 MHz.[27]

Prior to being injected into the main accelerator, the particles are prepared by a series of systems that successivelyincrease their energy. The first system is the linear particle accelerator LINAC 2 generating 50-MeV protons, whichfeeds the Proton Synchrotron Booster (PSB). There the protons are accelerated to 1.4 GeV and injected into theProton Synchrotron (PS), where they are accelerated to 26 GeV. Finally the Super Proton Synchrotron (SPS) is usedto further increase their energy to 450 GeV before they are at last injected (over a period of 20 minutes) into themain ring. Here the proton bunches are accumulated, accelerated (over a period of 20 minutes) to their peak 7-TeVenergy, and finally circulated for 10 to 24 hours while collisions occur at the four intersection points.[28]

CMS detector for LHC

The LHC physics program is mainly based on proton–proton collisions.However, shorter running periods, typically one month per year, with heavy-ioncollisions are included in the program. While lighter ions are considered as well,the baseline scheme deals with lead ions[29] (see A Large Ion ColliderExperiment). The lead ions will be first accelerated by the linear acceleratorLINAC 3, and the Low-Energy Ion Ring (LEIR) will be used as an ion storageand cooler unit. The ions will then be further accelerated by the PS and SPSbefore being injected into LHC ring, where they will reach an energy of 2.76TeV per nucleon (or 575 TeV per ion), higher than the energies reached by theRelativistic Heavy Ion Collider. The aim of the heavy-ion program is toinvestigate quark–gluon plasma, which existed in the early universe.

DetectorsSix detectors have been constructed at the LHC, located underground in large caverns excavated at the LHC'sintersection points. Two of them, the ATLAS experiment and the Compact Muon Solenoid (CMS), are large, generalpurpose particle detectors.[23] A Large Ion Collider Experiment (ALICE) and LHCb, have more specific roles andthe last two, TOTEM and LHCf, are very much smaller and are for very specialized research. The BBC's summaryof the main detectors is:[30]

Large Hadron Collider 15

Detector Description

ATLAS one of two general purpose detectors. ATLAS will be used to look for signs of new physics, including the origins of mass and extradimensions.

CMS the other general purpose detector will, like ATLAS, hunt for the Higgs boson and look for clues to the nature of dark matter.

ALICE is studying a "fluid" form of matter called quark–gluon plasma that existed shortly after the Big Bang.

LHCb equal amounts of matter and antimatter were created in the Big Bang. LHCb will try to investigate what happened to the "missing"antimatter.

Operational timelineThe first beam was circulated through the collider on the morning of 10 September 2008.[30] CERN successfullyfired the protons around the tunnel in stages, three kilometres at a time. The particles were fired in a clockwisedirection into the accelerator and successfully steered around it at 10:28 local time.[31] The LHC successfullycompleted its first major test: after a series of trial runs, two white dots flashed on a computer screen showing theprotons travelled the full length of the collider. It took less than one hour to guide the stream of particles around itsinaugural circuit.[32] CERN next successfully sent a beam of protons in a counterclockwise direction, taking slightlylonger at one and a half hours due to a problem with the cryogenics, with the full circuit being completed at 14:59.On 19 September 2008, a quench occurred in about 100 bending magnets in sectors 3 and 4, causing a loss ofapproximately six tonnes of liquid helium, which was vented into the tunnel, and a temperature rise of about 100kelvin in some of the affected magnets. Vacuum conditions in the beam pipe were also lost.[33] Shortly after theincident CERN reported that the most likely cause of the problem was a faulty electrical connection between twomagnets, and that – due to the time needed to warm up the affected sectors and then cool them back down tooperating temperature – it would take at least two months to fix it.[34] Subsequently, CERN released a preliminaryanalysis of the incident on 16 October 2008,[35] and a more detailed one on 5 December 2008.[36] Both analysesconfirmed that the incident was indeed initiated by a faulty electrical connection. A total of 53 magnets weredamaged in the incident and were repaired or replaced during the winter shutdown.[37]

In the original timeline of the LHC commissioning, the first "modest" high-energy collisions at a center-of-massenergy of 900 GeV were expected to take place before the end of September 2008, and the LHC was expected to beoperating at 10 TeV by the time of the official inauguration on 21 October 2008.[38] However, due to the delaycaused by the above-mentioned incident, the collider was not operational until November 2009.[39] Despite thedelay, LHC was officially inaugurated on 21 October 2008, in the presence of political leaders, science ministersfrom CERN's 20 Member States, CERN officials, and members of the worldwide scientific community.[40]

Most of 2009 was spent on repairs and reviews from the damage caused by the quench incident. On November 20,the first low-energy beams circulated in the tunnel for the first time since the incident. The early part of 2010 saw thecontinue ramp-up of beam in energies and early physics experiments. On 30 March 2010, LHC set a record forhigh-energy collisions, by colliding proton beams at a combined energy level of 7 TeV. The attempt was the thirdthat day, after two unsuccessful attempts in which the protons had to be "dumped" from the collider and new beamshad to be injected.[41] CERN has declared a schedule to operate the LHC through the rest of 2010 and most of 2011before the next scheduled shutdown.[42] The first proton run ended on 4 November 2010. A run with lead ions startedon 8 November 2010, and ended on 6 December 2010.[43] This allowed the ALICE experiment to study matter underextreme conditions similar to those shortly after the Big Bang.[44]

Large Hadron Collider 16

Timeline

Date Event

10 Sep 2008 CERN successfully fired the first protons around the entire tunnel circuit in stages.

19 Sep 2008 Magnetic quench occurred in about 100 bending magnets in sectors 3 and 4, causing a loss of approximately 6 tonnes of liquidhelium.

30 Sep 2008 First "modest" high-energy collisions planned but postponed due to accident.

16 Oct 2008 CERN released a preliminary analysis of the accident.

21 Oct 2008 Official inauguration.

5 Dec 2008 CERN released detailed analysis.

20 Nov 2009 Low-energy beams circulated in the tunnel for the first time since the accident.[45]

23 Nov 2009 First particle collisions in all four detectors at 450 GeV.[9]

30 Nov 2009 LHC becomes the world's highest-energy particle accelerator achieving 1.18 TeV per beam, beating the Tevatron's previous record of0.98 TeV per beam held for eight years.[46]

28 Feb 2010 The LHC continues operations ramping energies to run at 3.5 TeV for 18 months to two years, after which it will be shut down toprepare for the 14 TeV collisions (7 TeV per beam).[47]

30 Mar 2010 The two beams collided at 7 TeV (3.5 TeV per beam) in the LHC at 13:06 CEST, marking the start of the LHC research program.

8 Nov 2010 Start of the first run with lead ions.

6 Dec 2010 End of the run with lead ions. Shutdown until early 2011.

FindingsCERN scientists estimate that, if the Standard Model is correct, a single Higgs boson may be produced every fewhours. At this rate, it may take about two to three years to collect enough data to discover the Higgs bosonunambiguously. Similarly, it may take one year or more before sufficient results concerning supersymmetricparticles have been gathered to draw meaningful conclusions.[1] On the other hand, some extensions of the StandardModel predict additional particles, such as the heavy W' and Z' gauge bosons, whose existence might already beprobed after a few months of data taking.[48]

The first physics results from the LHC, involving 284 collisions which took place in the ALICE detector, werereported on 15 December 2009.[49] The results of the first proton–proton collisions at energies higher than Fermilab'sTevatron proton–antiproton collisions were published by the CMS collaboration in early February 2010, yieldinggreater-than-predicted charged-hadron production.[50] The CMS paper reports that the increase in the production rateof charged hadrons (mostly kaons and pions) when the center-of-mass energy goes from 0.9 TeV to 2.36 TeVexceeds by roughly 10% the predictions of the theoretical models used in the analysis.[51]

Large Hadron Collider 17

Proposed upgradeAfter some years of running, any particle physics experiment typically begins to suffer from diminishing returns:each additional year of operation discovers less than the year before. The way around the diminishing returns is toupgrade the experiment, either in energy or in luminosity. A luminosity upgrade of the LHC, called the Super LHC,has been proposed,[52] to be made after ten years of LHC operation.The optimal path for the LHC luminosity upgrade includes an increase in the beam current (i.e., the number ofprotons in the beams) and the modification of the two high-luminosity interaction regions, ATLAS and CMS. Toachieve these increases, the energy of the beams at the point that they are injected into the (Super) LHC should alsobe increased to 1 TeV. This will require an upgrade of the full pre-injector system, the needed changes in the SuperProton Synchrotron being the most expensive.

CostWith a budget of 9 billion US dollars (approx. €7.5bn or £6.19bn as of Jun 2010), the LHC is one of the mostexpensive scientific instruments[53] ever built.[54] The total cost of the project is expected to be of the order of 4.6bnSwiss francs (approx. $4.4bn, €3.1bn, or £2.8bn as of Jan 2010) for the accelerator and SFr 1.16bn (approx. $1.1bn,€0.8bn, or £0.7bn as of Jan 2010) for the CERN contribution to the experiments.[55]

The construction of LHC was approved in 1995 with a budget of SFr 2.6bn, with another SFr 210M towards theexperiments. However, cost overruns, estimated in a major review in 2001 at around SFr 480M for the accelerator,and SFr 50M for the experiments, along with a reduction in CERN's budget, pushed the completion date from 2005to April 2007.[56] The superconducting magnets were responsible for SFr 180M of the cost increase. There were alsofurther costs and delays due to engineering difficulties encountered while building the underground cavern for theCompact Muon Solenoid,[57] and also due to faulty parts provided by Fermilab.[58] Due to lower electricity costsduring the summer, it is expected that the LHC will normally not operate over the winter months,[59] although anexception was made to make up for the 2008 start-up delays over the 2009/10 winter.

Computing resourcesData produced by LHC as well as LHC-related simulation will produce a total data output of 15 petabytes per year(max throughput while running not stated).[60]

The LHC Computing Grid[61] is being constructed to handle the massive amounts of data produced. It incorporatesboth private fiber optic cable links and existing high-speed portions of the public Internet, enabling data transferfrom CERN to academic institutions around the world.The Open Science Grid is used as the primary infrastructure in the United States, and also as part of an interoperablefederation with the LHC Computing Grid.The distributed computing project LHC@home was started to support the construction and calibration of the LHC.The project uses the BOINC platform, enabling anybody with an internet connection to use their computer idle timeto simulate how particles will travel in the tunnel. With this information, the scientists will be able to determine howthe magnets should be calibrated to gain the most stable "orbit" of the beams in the ring.

Safety of particle collisionsThe experiments at the Large Hadron Collider sparked fears among the public that the particle collisions mightproduce doomsday phenomena, involving the production of stable microscopic black holes or the creation ofhypothetical particles called strangelets.[62] Two CERN-commissioned safety reviews examined these concerns andconcluded that the experiments at the LHC present no danger and that there is no reason for concern,[63] [64] [65] aconclusion expressly endorsed by the American Physical Society.[66]

Large Hadron Collider 18

Operational challengesThe size of the LHC constitutes an exceptional engineering challenge with unique operational issues on account ofthe amount of energy stored in the magnets and the beams.[28] [67] While operating, the total energy stored in themagnets is 10 GJ (equivalent to 2.4 tons of TNT) and the total energy carried by the two beams reaches 724 MJ (173kilograms of TNT).[68]

Loss of only one ten-millionth part (10−7) of the beam is sufficient to quench a superconducting magnet, while thebeam dump must absorb 362 MJ (87 kilograms of TNT) for each of the two beams. These energies are carried byvery little matter: under nominal operating conditions (2,808 bunches per beam, 1.15×1011 protons per bunch), thebeam pipes contain 1.0×10−9 gram of hydrogen, which, in standard conditions for temperature and pressure, wouldfill the volume of one grain of fine sand.

Construction accidents and delays• On 25 October 2005, José Pereira Lages, a technician, was killed in the LHC when a switchgear that was being

transported fell on him.[69]

• On 27 March 2007 a cryogenic magnet support broke during a pressure test involving one of the LHC's innertriplet (focusing quadrupole) magnet assemblies, provided by Fermilab and KEK. No one was injured. Fermilabdirector Pier Oddone stated "In this case we are dumbfounded that we missed some very simple balance offorces". This fault had been present in the original design, and remained during four engineering reviews over thefollowing years.[70] Analysis revealed that its design, made as thin as possible for better insulation, was not strongenough to withstand the forces generated during pressure testing. Details are available in a statement fromFermilab, with which CERN is in agreement.[71] [72] Repairing the broken magnet and reinforcing the eightidentical assemblies used by LHC delayed the startup date, then planned for November 2007.

• Problems occurred on 19 September 2008 during powering tests of the main dipole circuit, when an electricalfault in the bus between magnets caused a rupture and a leak of six tonnes of liquid helium. The operation wasdelayed for several months.[73] It is currently believed that a faulty electrical connection between two magnetscaused an arc, which compromised the liquid-helium containment. Once the cooling layer was broken, the heliumflooded the surrounding vacuum layer with sufficient force to break 10-ton magnets from their mountings. Theexplosion also contaminated the proton tubes with soot.[36] [74] This accident was more recently thoroughlydiscussed in a 22 February 2010 Superconductor Science and Technology article by CERN physicist LucioRossi.[75]

• Two vacuum leaks were identified in July 2009, and the start of operations was further postponed tomid-November 2009.[76]

Popular cultureThe Large Hadron Collider has gained considerable attention from outside the scientific community and its progressis followed by most popular science media. The LHC has also sparked the imaginations of authors of works offiction, such as novels, TV series, and video games, although descriptions of what it is, how it works, and projectedoutcomes of the experiments are often only vaguely accurate, occasionally causing concern among the generalpublic.The novel Angels & Demons, by Dan Brown, involves antimatter created at the LHC to be used in a weapon againstthe Vatican. In response CERN published a "Fact or Fiction?" page discussing the accuracy of the book's portrayal ofthe LHC, CERN, and particle physics in general.[77] The movie version of the book has footage filmed on-site at oneof the experiments at the LHC; the director, Ron Howard, met with CERN experts in an effort to make the science inthe story more accurate.[78]

In The Big Bang Theory, the episode "The Large Hadron Collision" features the Large Hadron Collider prominently.

Large Hadron Collider 19

The novel FlashForward, by Robert J. Sawyer, involves the search for the Higgs boson at the LHC. CERNpublished a "Science and Fiction" page interviewing Sawyer and physicists about the book and the TV series basedon it.[79]

CERN employee Katherine McAlpine's "Large Hadron Rap" [80][81] surpassed 6 million YouTube views.[82] [83]

The band Les Horribles Cernettes was founded by female members of CERN. The name was chosen so to have thesame initials as the LHC.[84] [85] They are the first band to have a site on the World Wide Web,[86] and their photothere was the first to ever appear on the Web.[87]

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php3?id_article=22468& ei=qIs-TPDAC8G88gaV7NmhBA& sa=X& oi=translate& ct=result& resnum=1& ved=0CBgQ7gEwAA& prev=/search?q=http:/ / www. lienmultimedia. com/ article. php3%3Fid_article%3D22468& hl=en& client=firefox-a& hs=yCb& rls=org.mozilla:en-US:official). Translate.google.com. . Retrieved 2010-10-29.

Large Hadron Collider 21

[55] "How much does it cost?" (http:/ / askanexpert. web. cern. ch/ AskAnExpert/ en/ Accelerators/ LHCgeneral-en. html#3). CERN. 2007. .Retrieved 2009-09-28.

[56] Luciano Maiani (16 October 2001). "LHC Cost Review to Completion" (http:/ / user. web. cern. ch/ User/ LHCCost/ 2001-10-16/LHCCostReview. html). CERN. . Retrieved 2001-01-15.

[57] Toni Feder (2001). "CERN Grapples with LHC Cost Hike" (http:/ / ptonline. aip. org/ journals/ doc/ PHTOAD-ft/ vol_54/ iss_12/ 21_2.shtml). Physics Today 54 (12): 21. doi:10.1063/1.1445534. .

[58] "Bursting magnets may delay CERN collider project" (http:/ / www. reuters. com/ article/ scienceNews/ idUSL054919720070405). Reuters.5 April 2007. . Retrieved 2009-09-28.

[59] Paul Rincon (23 September 2008). "Collider halted until next year" (http:/ / news. bbc. co. uk/ 1/ hi/ sci/ tech/ 7632408. stm). BBC News. .Retrieved 2009-09-28.

[60] "CERN LHC Computing" (http:/ / public. web. cern. ch/ public/ en/ LHC/ Computing-en. html). CERN. 2008. . Retrieved 2009-09-28.[61] http:/ / www. cite-sciences. fr/ francais/ ala_cite/ science_actualites/ sitesactu/ question_actu. php?langue=fr& id_article=16043, article de la

cité des sciences[62] Alan Boyle (2 September 2008). "Courts weigh doomsday claims" (http:/ / cosmiclog. msnbc. msn. com/ archive/ 2008/ 09/ 02/ 1326534.

aspx). Cosmic Log. MSNBC. . Retrieved 2009-09-28.[63] J.-P. Blaizot, J. Iliopoulos, J. Madsen, G.G. Ross, P. Sonderegger, H.-J. Specht (2003). "Study of Potentially Dangerous Events During

Heavy-Ion Collisions at the LHC" (http:/ / doc. cern. ch/ yellowrep/ 2003/ 2003-001/ p1. pdf). CERN. . Retrieved 2009-09-28.[64] J. Ellis J, G. Giudice, M.L. Mangano, T. Tkachev, U. Wiedemann (LHC Safety Assessment Group) (5 September 2008). "Review of the

Safety of LHC Collisions". Journal of Physics G 35: 115004. doi:10.1088/0954-3899/35/11/115004. arXiv:0806.3414.[65] "The safety of the LHC" (http:/ / public. web. cern. ch/ public/ en/ LHC/ Safety-en. html). CERN. 2008. . Retrieved 2009-09-28.[66] Division of Particles & Fields (http:/ / www. aps. org/ units/ dpf/ ). "Statement by the Executive Committee of the DPF on the Safety of

Collisions at the Large Hadron Collider" (http:/ / www. aps. org/ units/ dpf/ governance/ reports/ upload/ lhc_saftey_statement. pdf). AmericanPhysical Society. . Retrieved 2009-09-28.

[67] "Challenges in accelerator physics" (http:/ / lhc. web. cern. ch/ lhc/ general/ acphys. htm). CERN. 14 January 1999. . Retrieved 2009-09-28.[68] John Poole (2004). "Beam Parameters and Definitions" (https:/ / edms. cern. ch/ file/ 445830/ 5/ Vol_1_Chapter_2. pdf). .[69] CERN Press Office (26 October 2005). "Message from the Director-General" (http:/ / user. web. cern. ch/ user/ QuickLinks/

Announcements/ 2005/ Accident. html). Press release. . Retrieved 2009-09-28.[70] "Fermilab 'Dumbfounded' by fiasco that broke magnet" (http:/ / web. archive. org/ web/ 20080616063402/ http:/ / www. photonics. com/

content/ news/ 2007/ April/ 4/ 87089. aspx). Photonics.com. 4 April 2007. Archived from the original (http:/ / www. photonics. com/ content/news/ 2007/ April/ 4/ 87089. aspx) on 2008-06-16. . Retrieved 2009-09-28.

[71] CERN Press Office (1 June 2007). "Fermilab update on inner triplet magnets at LHC: Magnet repairs underway at CERN" (http:/ / user.web. cern. ch/ user/ QuickLinks/ Announcements/ 2007/ LHCInnerTriplet_5. html). Press release. . Retrieved 2009-09-28.

[72] "Updates on LHC inner triplet failure" (http:/ / www. fnal. gov/ pub/ today/ lhc_magnet_archive. html). Fermilab Today. Fermilab. 28September 2007. . Retrieved 2009-09-28.

[73] Paul Rincon (23 September 2008). "Collider halted until next year" (http:/ / news. bbc. co. uk/ 2/ hi/ in_depth/ 7632408. stm). BBC News. .Retrieved 2009-09-29.

[74] Dennis Overbye (5 December 2008). "After repairs, summer start-up planned for collider" (http:/ / www. nytimes. com/ 2008/ 12/ 06/science/ 06cern. html). New York Times. . Retrieved 2008-12-08.

[75] http:/ / www. iop. org/ EJ/ article/ 0953-2048/ 23/ 3/ 034001/ sust10_3_034001. pdf?request-id=70c5f5ed-6913-4a93-a944-14f91f848c14[76] "News on the LHC" (http:/ / user. web. cern. ch/ user/ news/ 2009/ 090716. html). CERN. 16 July 2009. . Retrieved 2009-09-28.[77] "Angels and Demons" (http:/ / public. web. cern. ch/ Public/ en/ Spotlight/ SpotlightAandD-en. html). CERN. January 2008. . Retrieved

2009-09-28.[78] Ceri Perkins (2 June 2008). "ATLAS gets the Hollywood treatment" (http:/ / atlas-service-enews. web. cern. ch/ atlas-service-enews/ news/

news_angelphoto. php). ATLAS e-News. . Retrieved 2009-09-28.[79] "FlashForward" (http:/ / flashforward. web. cern. ch/ flashforward/ ). CERN. September 2009. . Retrieved 2009-10-03.[80] http:/ / www. youtube. com/ watch?v=j50ZssEojtM[81] Katherine McAlpine (28 July 2008). "Large Hadron Rap" (http:/ / www. youtube. com/ watch?v=j50ZssEojtM). YouTube. . Retrieved

2009-09-28.[82] Roger Highfield (6 September 2008). "Rap about world's largest science experiment becomes YouTube hit" (http:/ / www. telegraph. co. uk/

earth/ main. jhtml?xml=/ earth/ 2008/ 08/ 26/ scirap126. xml). Telegraph (London). . Retrieved 2009-09-28.[83] Jennifer Bogo (1 August 2008). "Large Hadron Collider rap teaches particle physics in 4 minutes" (http:/ / www. popularmechanics. com/

blogs/ science_news/ 4276090. html). Popular Mechanics. . Retrieved 2009-09-28.[84] Malcolm W Brown (1998-12-29). "Physicists Discover Another Unifying Force: Doo-Wop" (http:/ / musiclub. web. cern. ch/ MusiClub/

bands/ cernettes/ Press/ NYT. pdf). New York Times (New York, USA). . Retrieved 2010-09-21.[85] Heather McCabe (Feb 10 1999). "Grrl Geeks Rock Out" (http:/ / musiclub. web. cern. ch/ MusiClub/ bands/ cernettes/ Press/ Wired. pdf).

Wired News. . Retrieved 2010-09-21.[86] James Gillies (6 September 2008). "Making a song and dance about physics" (http:/ / cerncourier. com/ cws/ article/ cern/ 27907). CERN

Courier (CERN). . Retrieved 2010-09-24.

Large Hadron Collider 22

[87] Silvano de Gennaro. "LHC: The First Band on the Web" (http:/ / musiclub. web. cern. ch/ MusiClub/ bands/ cernettes/ firstband. html).CERN MusiClub. CERN. . Retrieved 2010-09-24.

External links• Official website (http:/ / http:/ / lhc. web. cern. ch/ lhc/ )• Overview of the LHC at CERN's public webpage (http:/ / public. web. cern. ch/ public/ en/ LHC/ LHC-en. html)• CERN Courier magazine (http:/ / www. cerncourier. com/ )• CERN (http:/ / twitter. com/ cern) on Twitter• CMS Experiment at CERN (http:/ / twitter. com/ CMSExperiment) on Twitter• Unofficial CERN (http:/ / twitter. com/ LHCExperiment) on Twitter• LHC Portal (http:/ / www. lhcportal. com/ ) Web portal• Lyndon Evans and Philip Bryant (eds) (2008). "LHC Machine" (http:/ / www. iop. org/ EJ/ journal/ -page=extra.

lhc/ jinst). Journal of Instrumentation 3: S08001. doi:10.1088/1748-0221/3/08/S08001. Full documentation fordesign and construction of the LHC and its six detectors (1600p).

• symmetry magazine LHC special issue August 2006 (http:/ / www. symmetrymagazine. org/ cms/ ?pid=1000350),special issue December 2007 (http:/ / www. symmetrymagazine. org/ cms/ ?pid=1000562)

• New Yorker: Crash Course (http:/ / www. newyorker. com/ reporting/ 2007/ 05/ 14/ 070514fa_fact_kolbert). Theworld's largest particle accelerator.

• NYTimes: A Giant Takes On Physics' Biggest Questions (http:/ / www. nytimes. com/ 2007/ 05/ 15/ science/15cern. html?ex=1336881600& en=7825f6702d7071e7& ei=5090& partner=rssuserland& emc=rss).

• Why a Large Hadron Collider? (http:/ / seedmagazine. com/ news/ 2006/ 07/ why_a_large_hadron_collider. php)Seed Magazine interviews with physicists.

• Thirty collected pictures during commissioning and post- 19 September 2008 incident repair (http:/ / www.boston. com/ bigpicture/ 2009/ 11/ large_hadron_collider_ready_to. html), from Boston Globe.

• Podcast Interview (http:/ / omegataupodcast. net/ 2010/ 03/ 30-the-large-hadron-collider/ ) with CERN's RolfLandua about the LHC and the physics behind it

23

Experiments

List of LHC experimentsThis is a list of current and proposed experiments that take place, or would take place, at the CERN Large HadronCollider (LHC). The LHC is the most energetic particle collider in the world, and will be used to test the accuracy ofthe Standard Model (and particularly to search for the Higgs boson), and look for physics beyond the StandardModel such as supersymmetry, extra dimensions, and others.The list is first compiled from the SPIRES database, then missing information is retrieved from the online versionCERN's Grey Book. The most specific information of the two is kept, e.g. if the SPIRES database lists December2008, while the Grey Book lists 22 December 2008, the Grey Book entry is shown. When there is a conflict betweenthe SPIRES database and the Grey Book, the SPIRES database information is listed, unless otherwise noted.

Large Hadron Collider experiments

LHC experiments

Experiment Location Spokesperson Description Proposed Approved Began Completed Link Website

ALICE IP2 Hans H.Gutbrod,

Eugenio Nappi,Jurgen Schukraft

A large ion colliderexperiment: producingquark–gluon plasmaby colliding leadnuclei (~2.76 TeV)

?? 6 Feb1997

30March2010

N/A SPIRES[1]

Grey Book[2]

Website[3]

ATLAS IP1 FabiolaGianotti[4]

A toroidal LHCapparatus: sheddinglight on theinconsistencies of theStandard Model

Dec 1994 31 Jan1996

30March2010

N/A SPIRES[5]

Grey Book[6]

Website[7]

CMS IP5 Michel JeanDella Negra

Compact muonsolenoid: samepurpose as for ATLAS

Oct 1992 31 Jan1996

30March2010

N/A SPIRES[8]

Grey Book[9]

Website[10]

LHCb IP8 Tatsuya Nakada LHC beautyexperiment: measuringcertain B-hadronqualities such asasymmetries and CPviolations,

?? 17 Sep1998

30March2010

N/A SPIRES[11]

Grey Book[12]

Website[13]

LHCf IP1 Yasushi Muraki LHC-foward:measurement ofneutral 0π mesonproduction, in order tounderstand ultra highenergy cosmic rays

?? 12 May2004

Notyet

N/A Grey Book[14]

Website[15]

List of LHC experiments 24

FELIX IP4 Karsten Eggert,Cyrus Taylor

Forward elastic andinelastic experiment atthe LHC

?? ?? ?? ?? SPIRES[16]

Website[17]

FP420 IP1, IP5 Brian Cox Foward protondetectors at 420 m[from the ATLASand/or CMSinteraction point(s)]

?? ?? ?? ?? SPIRES[18]

Website[19]

HV-QF IP5 AntonioFerrando

Hadron very forwardcalorimeter, quartzfiber option

?? ?? ?? ?? SPIRES[20]

Website[21]

MOEDAL IP8 James L. Pinfold Monopole and exoticparticle detector at theLHC

July2009[22]

2December2009[23]

?? ?? SPIRES[24]

Website[25]

TOTEM IP5 Karsten Eggert Total cross section,elastic scattering anddiffractiondissociation at theLHC

1999 18 May1999

Notyet

N/A SPIRES[26]

Grey Book[27]

Website[28]

Notes[1] http:/ / www. slac. stanford. edu/ spires/ find/ experiments/ www2?ee=CERN-LHC-ALICE[2] http:/ / greybook. cern. ch/ programmes/ experiments/ ALICE. html[3] http:/ / aliceinfo. cern. ch/ Collaboration/ index. html[4] Previously Peter Jenni[5] http:/ / www. slac. stanford. edu/ spires/ find/ experiments/ www2?ee=CERN-LHC-ATLAS[6] http:/ / greybook. cern. ch/ programmes/ experiments/ ATLAS. html[7] http:/ / atlas. web. cern. ch/ Atlas/ index. html[8] http:/ / www. slac. stanford. edu/ spires/ find/ experiments/ www2?ee=CERN-LHC-CMS[9] http:/ / greybook. cern. ch/ programmes/ experiments/ CMS. html[10] http:/ / cms. cern. ch/ iCMS/[11] http:/ / www. slac. stanford. edu/ spires/ find/ experiments/ www2?ee=CERN-LHC-B[12] http:/ / greybook. cern. ch/ programmes/ experiments/ LHCB. html[13] http:/ / lhcb. web. cern. ch/ lhcb/[14] http:/ / greybook. cern. ch/ programmes/ experiments/ LHCF. html[15] http:/ / www. stelab. nagoya-u. ac. jp/ LHCf/[16] http:/ / www. slac. stanford. edu/ spires/ find/ experiments/ www2?ee=CERN-LHC-FELIX[17] http:/ / felix. web. cern. ch/ FELIX/[18] http:/ / www. slac. stanford. edu/ spires/ find/ experiments/ www2?ee=CERN-LHC-FP420[19] http:/ / www. fp420. com/[20] http:/ / www. slac. stanford. edu/ spires/ find/ experiments/ www2?ee=CERN-LHC-HV-QF[21] http:/ / budoe. bu. edu/ ~sullivan/[22] James Pinfold (2010). "The MoEDAL TDR" (http:/ / web. me. com/ jamespinfold/ MoEDAL_site/ TDR. html). . Retrieved 2010-04-11.[23] James Pinfold (2010). "CERN Research Board Approves the MoEDAL Experiment" (http:/ / web. me. com/ jamespinfold/ MoEDAL_site/

MoEDAL_Milestones/ Entries/ 2009/ 12/ 2_CERN_Research_Board_Approves_the_MoEDAL_Experiment. html). The MoEDAL MilestoneBlog. . Retrieved 2010-04-11.

[24] http:/ / www. slac. stanford. edu/ spires/ find/ experiments/ www2?ee=CERN-LHC-MOEDAL[25] http:/ / web. me. com/ jamespinfold/ MoEDAL_site/ Welcome. html[26] http:/ / www. slac. stanford. edu/ spires/ find/ experiments/ www2?ee=CERN-LHC-TOTEM[27] http:/ / greybook. cern. ch/ programmes/ experiments/ TOTEM. html[28] http:/ / totem. web. cern. ch/ Totem/

List of LHC experiments 25

References• SPIRES team (http:/ / www. slac. stanford. edu/ spires/ about/ people. shtml). "SPIRES database" (http:/ / www.

slac. stanford. edu/ spires/ hep/ ). Stanford Linear Accelerator Center. Retrieved 2009-09-15.• GS-AIF-FPF (http:/ / ais. web. cern. ch/ ais/ manpower/ ). "Grey Book" (http:/ / greybook. cern. ch/ ). CERN.

Retrieved 2009-09-15.

External links• CERN website (http:/ / public. web. cern. ch/ public/ )

• LHC website (http:/ / lhc. web. cern. ch/ lhc/ )• CERN Grey Book (http:/ / greybook. cern. ch/ )• SPIRES database (http:/ / www. slac. stanford. edu/ spires/ )

ALICE 26

ALICE

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton Synchrotron

SPS Super Proton Synchrotron

ALICE (A Large Ion Collider Experiment) is one of the six detector experiments at the Large Hadron Collider atCERN. The other five are: ATLAS, CMS, TOTEM, LHCb, and LHCf. ALICE is optimized to study heavy ioncollisions. Pb-Pb nuclei collisions will be studied at a centre of mass energy of 2.76 TeV per nucleon. The resultingtemperature and energy density are expected to be large enough to generate a quark-gluon plasma, a state of matterwherein quarks and gluons are deconfined.

Inner Tracking SystemThe Inner Tracking System (ITS) consists of six cylindrical layers of silicon detectors. The layers surround thecollision point and measure the properties of the emerging particles, pin-pointing their positions to a fraction of amillimetre. The ITS will recognize particles containing heavy quarks by identifying the points at which they decay.ITS layers (counting from the interaction point):• 2 layers of SPD (Silicon Pixel Detector),• 2 layers of SDD (Silicon Drift Detector),• 2 layers of SSD (Silicon Strip Detector).

ALICE 27

Time Projection ChamberThe ALICE Time Projection Chamber (TPC) is the main particle tracking device in ALICE. Charged particlescrossing the gas of the TPC ionize the gas atoms along their path, liberating electrons that drift towards the endplates of the detector. An avalanche effect in the vicinity of the anode wires strung in the readout, will give thenecessary signal amplification. The positive ions created in the avalanche will induce a positive current signal on thepad plane. The readout is done by the 557 568 pads that form the cathode plane of the multi-wire proportionalchambers (MWPC) located at the end plates. This gives the r and coordinates. The last coordinate, z, is given bythe drift time.

Transition Radiation Detector

The completed ALICE detector showing theeighteen TRD modules (trapezoidal prisms in a

radial arrangement).

Electrons and positrons can be discriminated from other chargedparticles using the emission of transition radiation, X-rays emittedwhen the particles cross many layers of thin materials. To develop sucha Transition Radiation Detector (TRD) for ALICE many detectorprototypes were tested in mixed beams of pions and electrons.

Time of Flight

Charged particles are identified in ALICE by Time-Of-Flight (TOF);heavier particles are slower and so take longer to reach the outer layersof the detector. For its TOF system ALICE uses detectors calledMultigap Resistive Plate Chambers (MRPC). There are approximately160 000 MRPC pads with time resolution of about 100 ps distributedover the large surface of 150 square meters. Using the tracking information from other detectors every track firing asensor is identified.

Photon SpectrometerThe Photon Spectrometer (PHOS) is designed to measure the temperature of collisions by detecting photonsemerging from them. It will be made of lead tungstate crystals. When high energy photons strike lead tungstate, theymake it glow, or scintillate, and this glow can be measured. Lead tungstate is extremely dense (denser than iron),stopping most photons that reach it.

High Momentum Particle Identification DetectorThe High Momentum Particle Identification Detector (HMPID) is a RICH detector to determine the speed ofparticles beyond the momentum range available through energy loss (in ITS and TPC, p = 600 MeV) and throughtime-of-flight measurements (in TOF, p = 1.2–1.4 GeV). Its momentum range is up to 3 GeV for pion/kaondiscrimination and up to 5 GeV for kaon/proton discrimination. It is the world's largest caesium iodide RICHdetector, with an active area of 11 m². A prototype was successfully tested at CERN in 1997 and currently takes dataat the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory in the US.

ALICE 28

Muon spectrometerThe muon spectrometer measures pairs of muons, in particular those coming from the decays of J/ψ and Upsilonparticles. Tracking chambers to detect the muons and reconstruct their trajectories will be made from a specialcomposite material, which is highly rigid but very thin. A set of resistive plate chambers (RPC) will act as atriggering device.

Forward Multiplicity DetectorsThe Forward Multiplicity Detectors (FMD) consist of 5 large silicon discs with each 10 240 individual detectorchannels to measure the charged particles emitted at small angles relative to the beam. The forward detectors alsocomprise the main trigger detectors for timing (T0) and for collision centrality (V0). Another important forwarddetector in ALICE is the Photon Multiplicity Detector (PMD). This is a pre-shower detector which measures themultiplicity and spatial distribution of photons produced in the collisions.

Electro-Magnetic CalorimeterThe Electro-Magnetic Calorimeter (EM-Cal) will add greatly to the high momentum particle measurementcapabilities of ALICE.

External links• Official ALICE Public Webpage [1] at CERN• ALICE section on US/LHC Website [2]

• ALICE photography panorama [3]

• Photography panorama of ALICE detector center [4]

• K. Aamodt et al. (ALICE collaboration) (2008). "The ALICE experiment at the CERN LHC" [5]. Journal ofInstrumentation 3 (8): S08002. doi:10.1088/1748-0221/3/08/S08002. (Full design documentation)

References[1] http:/ / aliceinfo. cern. ch/ Public/ Welcome. html[2] http:/ / www. uslhc. us/ What_is_the_LHC/ Experiments/ ALICE[3] http:/ / petermccready. com/ portfolio/ 07041606. html[4] http:/ / petermccready. com/ portfolio/ 07041607. html[5] http:/ / www. iop. org/ EJ/ journal/ -page=extra. lhc/ jinst

ATLAS 29

ATLAS

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton Synchrotron

SPS Super Proton Synchrotron

Geographical coordinates: 46°14′8″N 6°3′19″E

ATLAS logo.

ATLAS (A Toroidal LHC ApparatuS) is one of the six particle detectorexperiments (ALICE, ATLAS, CMS, TOTEM, LHCb, and LHCf) constructed atthe Large Hadron Collider (LHC), a new particle accelerator at the EuropeanOrganization for Nuclear Research (CERN) in Switzerland. ATLAS is 44 metreslong and 25 metres in diameter, weighing about 7,000 tonnes. The project is led byFabiola Gianotti and involves roughly 2,000 scientists and engineers at 165institutions in 35 countries.[1] The construction was originally scheduled to becompleted in June 2007, but was ready and detected its first beam events on 10September 2008.[2] The experiment is designed to observe phenomena that involvehighly massive particles which were not observable using earlier lower-energyaccelerators and might shed light on new theories of particle physics beyond theStandard Model.

The ATLAS collaboration, the group of physicists building the detector, wasformed in 1992 when the proposed EAGLE (Experiment for Accurate Gamma,Lepton and Energy Measurements) and ASCOT (Apparatus with Super

COnducting Toroids) collaborations merged their efforts into building a single, general-purpose particle detector for

the Large Hadron Collider.[3] The design was a combination of those two previous designs, as well as the detector research and development that had been done for the Superconducting Supercollider. The ATLAS experiment was

ATLAS 30

proposed in its current form in 1994, and officially funded by the CERN member countries beginning in 1995.Additional countries, universities, and laboratories joined in subsequent years, and further institutions and physicistscontinue to join the collaboration even today. The work of construction began at individual institutions, with detectorcomponents shipped to CERN and assembled in the ATLAS experimental pit beginning in 2003.ATLAS is designed as a general-purpose detector. When the proton beams produced by the Large Hadron Colliderinteract in the center of the detector, a variety of different particles with a broad range of energies may be produced.Rather than focusing on a particular physical process, ATLAS is designed to measure the broadest possible range ofsignals. This is intended to ensure that, whatever form any new physical processes or particles might take, ATLASwill be able to detect them and measure their properties. Experiments at earlier colliders, such as the Tevatron andLarge Electron-Positron Collider, were designed based on a similar philosophy. However, the unique challenges ofthe Large Hadron Collider—its unprecedented energy and extremely high rate of collisions—require ATLAS to belarger and more complex than any detector ever built.

Background

ATLAS experiment detector under constructionin October 2004 in its experimental pit; the

current status of construction can be seen on theCERN website.[4] Note the people in the

background, for comparison.

The first cyclotron, an early type of particle accelerator, was built byErnest O. Lawrence in 1931, with a radius of just a few centimetresand a particle energy of 1 megaelectronvolt (MeV). Since then,accelerators have grown enormously in the quest to produce newparticles of greater and greater mass. As accelerators have grown, sotoo has the list of known particles that they might be used toinvestigate. The most comprehensive model of particle interactionsavailable today is known as the Standard Model of Particle Physics.With the important exception of the Higgs boson, all of the particlespredicted by the model have been observed. While the standard modelpredicts that quarks, electrons, and neutrinos should exist, it does notexplain why the masses of the particles are so very different. Due tothis violation of "naturalness" most particle physicists believe it ispossible that the Standard Model will break down at energies beyondthe current energy frontier of about one teraelectronvolt (TeV) (set at the Tevatron). If suchbeyond-the-Standard-Model physics is observed it is hoped that a new model, which is identical to the StandardModel at energies thus far probed, can be developed to describe particle physics at higher energies. Most of thecurrently proposed theories predict new higher-mass particles, some of which are hoped to be light enough to beobserved by ATLAS. At 27 kilometres in circumference, the Large Hadron Collider (LHC) will collide two beams ofprotons together, each proton carrying about 7 TeV of energy — enough energy to produce particles with masses upto roughly ten times more massive than any particles currently known — assuming of course that such particlesexist. With an energy seven million times that of the first accelerator the LHC represents a "new generation" ofparticle accelerators.

Particles that are produced in accelerators must also be observed, and this is the task of particle detectors. While interesting phenomena may occur when protons collide it is not enough to just produce them. Particle detectors must be built to detect particles, their masses, momentum, energies, charges, and nuclear spins. In order to identify all particles produced at the interaction point where the particle beams collide, particle detectors are usually designed with a similarity to an onion. The layers are made up of detectors of different types, each of which is adept at observing specific types of particles. The different features that particles leave in each layer of the detector allow for effective particle identification and accurate measurements of energy and momentum. (The role of each layer in the detector is discussed below.) As the energy of the particles produced by the accelerator increases, the detectors attached to it must grow to effectively measure and stop higher-energy particles. ATLAS is the largest detector ever

ATLAS 31

built at a particle collider as of 2008.[1]

Physics Program

A schematic, called a Feynman diagram, of twovirtual gluons from colliding LHC protonsinteracting to produce a hypothetical Higgs

boson, a top quark, and an antitop quark. These inturn decay into a specific combination of quarksand leptons that is very unlikely to be duplicatedby other processes. Collecting sufficient evidence

of signals like this one may eventually allowATLAS collaboration members to discover the

Higgs boson.

ATLAS is intended to investigate many different types of physics thatmight become detectable in the energetic collisions of the LHC. Someof these are confirmations or improved measurements of the StandardModel, while many others are searches for new physical theories.

One of the most important goals of ATLAS is to investigate a missingpiece of the Standard Model, the Higgs boson.[5] The Higgsmechanism, which includes the Higgs boson, is invoked to give massesto elementary particles, giving rise to the differences between the weakforce and electromagnetism by giving the W and Z bosons masseswhile leaving the photon massless. If the Higgs boson is not discoveredby ATLAS, it is expected that another mechanism of electroweaksymmetry breaking that explains the same phenomena, such astechnicolour, will be discovered. The Standard Model is simply notmathematically consistent at the energies of the LHC without such amechanism. The Higgs boson would be detected by the particles itdecays into; the easiest to observe are two photons, two bottom quarks,or four leptons. Sometimes these decays can only be definitivelyidentified as originating with the Higgs boson when they are associatedwith additional particles; for an example of this, see the diagram atright.

The asymmetry between the behavior of matter and antimatter, known as CP violation, will also be investigated.[5]

Current CP-violation experiments, such as BaBar and Belle, have not yet detected sufficient CP violation in theStandard Model to explain the lack of detectable antimatter in the universe. It is possible that new models of physicswill introduce additional CP violation, shedding light on this problem; these models might either be detected directlyby the production of new particles, or indirectly by measurements made of the properties of B-mesons. (LHCb, anLHC experiment dedicated to B-mesons, is likely to be better suited to the latter).[6]

The top quark, discovered at Fermilab in 1995, has thus far had its properties measured only approximately. Withmuch greater energy and greater collision rates, LHC will produce a tremendous number of top quarks, allowingATLAS to make much more precise measurements of its mass and interactions with other particles.[7] Thesemeasurements will provide indirect information on the details of the Standard Model, perhaps revealinginconsistencies that point to new physics. Similar precision measurements will be made of other known particles; forexample, ATLAS may eventually measure the mass of the W boson twice as accurately as has previously beenachieved.Perhaps the most exciting lines of investigation are those searching directly for new models of physics. One theorythat is the subject of much current research is broken supersymmetry. The theory is popular because it couldpotentially solve a number of problems in theoretical physics and is present in almost all models of string theory.Models of supersymmetry involve new, highly massive particles; in many cases these decay into high-energy quarksand stable heavy particles that are very unlikely to interact with ordinary matter. The stable particles would escapethe detector, leaving as a signal one or more high-energy quark jets and a large amount of "missing" momentum.Other hypothetical massive particles, like those in Kaluza-Klein theory, might leave a similar signature, but itsdiscovery would certainly indicate that there was some kind of physics beyond the Standard Model.

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One remote possibility (if the universe contains large extra dimensions) is that microscopic black holes might beproduced by the LHC.[8] These would decay immediately by means of Hawking radiation, producing all particles inthe Standard Model in equal numbers and leaving an unequivocal signature in the ATLAS detector.[9] In fact, if thisoccurs, the primary studies of Higgs bosons and top quarks would be conducted on those produced by the blackholes.

ComponentsThe ATLAS detector consists of a series of ever-larger concentric cylinders around the interaction point where theproton beams from the LHC collide. It can be divided into four major parts: the Inner Detector, the calorimeters, themuon spectrometer and the magnet systems.[10] Each of these is in turn made of multiple layers. The detectors arecomplementary: the Inner Detector tracks particles precisely, the calorimeters measure the energy of easily stoppedparticles, and the muon system makes additional measurements of highly penetrating muons. The two magnetsystems bend charged particles in the Inner Detector and the muon spectrometer, allowing their momenta to bemeasured.The only established stable particles that cannot be detected directly are neutrinos; their presence is inferred bynoticing a momentum imbalance among detected particles. For this to work, the detector must be "hermetic", anddetect all non-neutrinos produced, with no blind spots. Maintaining detector performance in the high radiation areasimmediately surrounding the proton beams is a significant engineering challenge.

Inner detector

The ATLAS TRT central section, the outermostpart of the Inner Detector, as of September 2005,

assembled on the surface and taking data fromcosmic rays.

The Inner Detector begins a few centimetres from the proton beamaxis, extends to a radius of 1.2 metres, and is seven metres in lengthalong the beam pipe. Its basic function is to track charged particles bydetecting their interaction with material at discrete points, revealingdetailed information about the type of particle and its momentum.[11]

The magnetic field surrounding the entire inner detector causescharged particles to curve; the direction of the curve reveals a particle'scharge and the degree of curvature reveals its momentum. The startingpoints of the tracks yield useful information for identifying particles;for example, if a group of tracks seem to originate from a point otherthan the original proton–proton collision, this may be a sign that theparticles came from the decay of a bottom quark (see B-tagging). TheInner Detector has three parts, which are explained below.

The Pixel Detector, the innermost part of the detector, contains three layers and three disks on each end-cap, with atotal of 1744 modules, each measuring two centimetres by six centimetres. The detecting material is 250 µm thicksilicon. Each module contains 16 readout chips and other electronic components. The smallest unit that can be readout is a pixel (each 50 by 400 micrometres); there are roughly 47,000 pixels per module. The minute pixel size isdesigned for extremely precise tracking very close to the interaction point. In total, the Pixel Detector will have over80 million readout channels, which is about 50% of the total readout channels; such a large count created a designand engineering challenge. Another challenge was the radiation the Pixel Detector will be exposed to because of itsproximity to the interaction point, requiring that all components be radiation hardened in order to continue operatingafter significant exposures.

The Semi-Conductor Tracker (SCT) is the middle component of the inner detector. It is similar in concept andfunction to the Pixel Detector but with long, narrow strips rather than small pixels, making coverage of a larger areapractical. Each strip measures 80 micrometres by 12.6 centimetres. The SCT is the most critical part of the inner

ATLAS 33

detector for basic tracking in the plane perpendicular to the beam, since it measures particles over a much larger areathan the Pixel Detector, with more sampled points and roughly equal (albeit one dimensional) accuracy. It iscomposed of four double layers of silicon strips, and has 6.2 million readout channels and a total area of 61 squaremeters.The Transition radiation tracker (TRT), the outermost component of the inner detector, is a combination of a strawtracker and a transition radiation detector. The detecting elements are drift tubes (straws), each four millimetres indiameter and up to 144 centimetres long. The uncertainty of track position measurements (position resolution) isabout 200 micrometres, not as precise as those for the other two detectors, a necessary sacrifice for reducing the costof covering a larger volume and having transition radiation detection capability. Each straw is filled with gas thatbecomes ionized when a charged particle passes through. The straws are held at about -1500V, driving the negativeions to a fine wire down the centre of each straw, producing a current pulse (signal) in the wire. The wires withsignals create a pattern of 'hit' straws that allow the path of the particle to be determined. Between the straws,materials with widely varying indices of refraction cause ultra-relativistic charged particles to produce transitionradiation and leave much stronger signals in some straws. Xenon gas is used to increase the number of straws withstrong signals. Since the amount of transition radiation is greatest for highly relativistic particles (those with a speedvery near the speed of light), and particles of a particular energy have a higher speed the lighter they are, particlepaths with many very strong signals can be identified as the lightest charged particles, electrons. The TRT has about298,000 straws in total.

Calorimeters

September 2005: the main barrel section of theATLAS hadronic calorimeter, waiting to be

moved inside the toroid magnets.

One of the sections of the extensions of thehadronic calorimeter, waiting to be inserted in

late February 2006

The calorimeters are situated outside the solenoidal magnet thatsurrounds the inner detector. Their purpose is to measure the energyfrom particles by absorbing it. There are two basic calorimetersystems: an inner electromagnetic calorimeter and an outer hadroniccalorimeter.[12] Both are sampling calorimeters; that is, they absorbenergy in high-density metal and periodically sample the shape of theresulting particle shower, inferring the energy of the original particlefrom this measurement.

The electromagnetic (EM) calorimeter absorbs energy from particlesthat interact electromagnetically, which include charged particles andphotons. It has high precision, both in the amount of energy absorbedand in the precise location of the energy deposited. The angle betweenthe particle's trajectory and the detector's beam axis (or more preciselythe pseudorapidity) and its angle within the perpendicular plane areboth measured to within roughly 0.025 radians. The energy-absorbingmaterials are lead and stainless steel, with liquid argon as the samplingmaterial, and a cryostat is required around the EM calorimeter to keepit sufficiently cool.

The hadron calorimeter absorbs energy from particles that pass throughthe EM calorimeter, but do interact via the strong force; these particlesare primarily hadrons. It is less precise, both in energy magnitude andin the localization (within about 0.1 radians only).[6] Theenergy-absorbing material is steel, with scintillating tiles that samplethe energy deposited. Many of the features of the calorimeter are chosen for their cost-effectiveness; the instrument

ATLAS 34

is large and comprises a huge amount of construction material: the main part of the calorimeter—the tilecalorimeter—is eight metres in diameter and covers 12 metres along the beam axis. The far-forward sections of thehadronic calorimeter are contained within the EM calorimeter's cryostat, and use liquid argon as it does.

Muon spectrometerThe muon spectrometer is an extremely large tracking system, extending from a radius of 4.25 m around thecalorimeters out to the full radius of the detector (11 m).[10] Its tremendous size is required to accurately measure themomentum of muons, which penetrate other elements of the detector; the effort is vital because one or more muonsare a key element of a number of interesting physical processes, and because the total energy of particles in an eventcould not be measured accurately if they were ignored. It functions similarly to the inner detector, with muonscurving so that their momentum can be measured, albeit with a different magnetic field configuration, lower spatialprecision, and a much larger volume. It also serves the function of simply identifying muons—very few particles ofother types are expected to pass through the calorimeters and subsequently leave signals in the muon spectrometer. Ithas roughly one million readout channels, and its layers of detectors have a total area of 12,000 square meters.

Magnet system

The ends of four of eight ATLAS toroid magnets,seen from the surface, about 90 metres above, in

September 2005.

The ATLAS detector uses two large superconducting magnet systemsto bend charged particles so that their momenta can be measured. Thisbending is due to the Lorentz force, which is proportional to velocity.Since all particles produced in the LHC's proton collisions will betraveling at very close to the speed of light, the force on particles ofdifferent momenta is equal. (In the theory of relativity, momentum isnot proportional to velocity at such speeds.) Thus high-momentumparticles will curve very little, while low-momentum particles willcurve significantly; the amount of curvature can be quantified and theparticle momentum can be determined from this value.

The inner solenoid produces a two tesla magnetic field surrounding theInner Detector.[13] This high magnetic field allows even very energeticparticles to curve enough for their momentum to be determined, and its nearly uniform direction and strength allowmeasurements to be made very precisely. Particles with momenta below roughly 400 MeV will be curved so stronglythat they will loop repeatedly in the field and most likely not be measured; however, this energy is very smallcompared to the several TeV of energy released in each proton collision.

The outer toroidal magnetic field is produced by eight very large air-core superconducting barrel loops and twoend-caps, all situated outside the calorimeters and within the muon system.[13] This magnetic field is 26 metres longand 20 metres in diameter, and it stores 1.6 gigajoules of energy. Its magnetic field is not uniform, because asolenoid magnet of sufficient size would be prohibitively expensive to build. Fortunately, measurements need to bemuch less precise to measure momentum accurately in the large volume of the muon system.

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Part of the ATLAS, as it looked February 2007.

Forward detectors

The ATLAS detector will be complemented with a set of detectors inthe very forward region. These detectors will be located in the LHCtunnel far away from the interaction point. The basic idea is to measureelastic scattering at very small angles in order to get a handle on theabsolute luminosity at the interaction point of ATLAS.

Data systems and analysisThe detector generates unmanageably large amounts of raw data, about 25 megabytes per event (raw; zerosuppression reduces this to 1.6 MB)times 23 events per beam crossing, times 40 million beam crossings per secondin the center of the detector, for a total of 23 petabyte/second of raw data.[14] The trigger system uses simpleinformation to identify, in real time, the most interesting events to retain for detailed analysis. There are three triggerlevels, the first based in electronics on the detector and the other two primarily run on a large computer cluster nearthe detector. After the first-level trigger, about 100,000 events per second have been selected. After the third-leveltrigger, a few hundred events remain to be stored for further analysis. This amount of data will require over100 megabytes of disk space per second — at least a petabyte each year.[15]

Offline event reconstruction will be performed on all permanently stored events, turning the pattern of signals fromthe detector into physics objects, such as jets, photons, and leptons. Grid computing will be extensively used forevent reconstruction, allowing the parallel use of university and laboratory computer networks throughout the worldfor the CPU-intensive task of reducing large quantities of raw data into a form suitable for physics analysis. Thesoftware for these tasks has been under development for many years, and will continue to be refined once theexperiment is running.Individuals and groups within the collaboration will write their own code to perform further analysis of these objects,searching in the pattern of detected particles for particular physical models or hypothetical particles. These studiesare already being developed and tested on detailed simulations of particles and their interactions with the detector.Such simulations give physicists a good sense of which new particles can be detected and how long it will take toconfirm them with sufficient statistical certainty.

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Notes[1] CERN (2006-11-20). "World's largest superconducting magnet switches on" (http:/ / press. web. cern. ch/ Press/ PressReleases/

Releases2006/ PR17. 06E. html). Press release. . Retrieved 2007-03-03.[2] "First beam and first events in ATLAS" (http:/ / www. atlas. ch/ news/ 2008/ first-beam-and-event. html). Atlas.ch. . Retrieved 2008-09-13.[3] "ATLAS Collaboration records" (http:/ / library. cern. ch/ archives/ isad/ isaatlas. html). CERN Archive. . Retrieved 2007-02-25.[4] "UX15 Installation; WEB cameras" (http:/ / atlaseye-webpub. web. cern. ch/ atlaseye-webpub/ web-sites/ pages/ UX15_webcams. htm).

ATLAS Control Room. cern.ch. . Retrieved September 15, 2010.[5] "Introduction and Overview" (http:/ / atlas. web. cern. ch/ Atlas/ TP/ NEW/ HTML/ tp9new/ node4.

html#SECTION00400000000000000000). ATLAS Technical Proposal. CERN. 1994. .[6] N. V. Krasnikov, V. A. Matveev (September 1997). "Physics at LHC" (http:/ / arxiv. org/ abs/ hep-ph/ 9703204). Physics of Particles and

Nuclei 28 (5): 441–470. doi:10.1134/1.953049. .[7] "Top-Quark Physics" (http:/ / atlas. web. cern. ch/ Atlas/ TP/ NEW/ HTML/ tp9new/ node416. html#SECTION0024100000000000000000).

ATLAS Technical Proposal. CERN. 1994. .[8] C.M. Harris, M.J. Palmer, M.A. Parker, P. Richardson, A. Sabetfakhri and B.R. Webber (2005). "Exploring higher dimensional black holes at

the Large Hadron Collider". Journal of High Energy Physics 5: 053. doi:10.1088/1126-6708/2005/05/053.[9] J. Tanaka, T. Yamamura, S. Asai, J. Kanzaki (2005). "Study of Black Holes with the ATLAS detector at the LHC" (http:/ / www.

springerlink. com/ content/ x067g845688470r4/ ). The European Physical Journal C 41 (s2): 19–33. doi:10.1140/epjcd/s2005-02-008-x. .[10] "Overall detector concept" (http:/ / atlas. web. cern. ch/ Atlas/ TP/ NEW/ HTML/ tp9new/ node6. html#SECTION00420000000000000000).

ATLAS Technical Proposal. CERN. 1994. .[11] "Inner detector" (http:/ / atlas. web. cern. ch/ Atlas/ TP/ NEW/ HTML/ tp9new/ node10. html#SECTION00433000000000000000). ATLAS

Technical Proposal. CERN. 1994. .[12] "Calorimetry" (http:/ / atlas. web. cern. ch/ Atlas/ TP/ NEW/ HTML/ tp9new/ node9. html#SECTION00432000000000000000). ATLAS

Technical Proposal. CERN. 1994. .[13] "Magnet system" (http:/ / atlas. web. cern. ch/ Atlas/ TP/ NEW/ HTML/ tp9new/ node8. html#SECTION00431000000000000000). ATLAS

Technical Proposal. CERN. 1994. .[14] . http:/ / atlas. ch/ detector. html. See also 32:30 for information on the various trigger levels.[15] "The sensitive giant" (http:/ / www. eurekalert. org/ features/ doe/ 2004-03/ dnal-tsg032604. php). United States Department of Energy

Research News. March 2004. .

References• ATLAS Technical Proposal. (http:/ / atlas. web. cern. ch/ Atlas/ TP/ tp. html) CERN: The Atlas Experiment.

Retrieved on 2007-04-10• ATLAS Detector and Physics Performance Technical Design Report. (http:/ / atlas. web. cern. ch/ Atlas/

GROUPS/ PHYSICS/ TDR/ access. html) CERN: The Atlas Experiment. Retrieved on 2007-04-10• N. V. Krasnikov, V. A. Matveev (September 1997). "Physics at LHC" (http:/ / arxiv. org/ abs/ hep-ph/ 9703204).

Physics of Particles and Nuclei 28 (5): 441–470. doi:10.1134/1.953049.

External links• Official ATLAS Public Webpage (http:/ / atlas. ch) at CERN (The "award winning ATLAS movie" is a very good

general introduction!)• Official ATLAS Collaboration Webpage (http:/ / atlas. web. cern. ch/ Atlas/ internal/ Welcome. html) at CERN

(Lots of technical and logistical information)• ATLAS Cavern Webcams (http:/ / atlaseye-webpub. web. cern. ch/ atlaseye-webpub/ web-sites/ pages/

UX15_webcams. htm)• Time lapse video of the assembly (http:/ / www. youtube. com/ watch?v=kVrUR_SOykk)• ATLAS section from US/LHC Website (http:/ / www. uslhc. us/ What_is_the_LHC/ Experiments/ ATLAS)• PhysicsWorld article on LHC and experiments (http:/ / physicsweb. org/ articles/ world/ 13/ 5/ 9/ 1)• New York Times article on LHC and experiments (http:/ / www. nytimes. com/ 2000/ 11/ 21/ science/ 21HIGG.

html?ex=1130040000& en=5282f51cf019f1b7& ei=5070& ex=1082001600& en=39ccf65ca6047eb2& ei=5070)• United States Department of Energy article on ATLAS (http:/ / www. eurekalert. org/ features/ doe/ 2004-03/

dnal-tsg032604. php)

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• The Large Hadron Collider ATLAS Experiment Virtual Reality (VR) photography panoramas (http:/ / www.petermccready. com/ portfolio/ 05091901. html)

• Large Hadron Collider Project Director Dr Lyn Evans CBE on the engineering behind the ATLAS experiment,Ingenia magazine, June 2008 (http:/ / www. ingenia. org. uk/ ingenia/ articles. aspx?Index=489)

• Atlas Experiment News and social networking (http:/ / www. AtlasExperiment. net)• The ATLAS Collaboration, G Aad et al. (2008-08-14). "The ATLAS Experiment at the CERN Large Hadron

Collider" (http:/ / www. iop. org/ EJ/ journal/ -page=extra. lhc/ jinst). Journal of Instrumentation 3 (S08003):S08003. doi:10.1088/1748-0221/3/08/S08003. Retrieved 2008-08-26. (Full design documentation)

• Press release from October 2008 by EB Industries regarding the ATLAS project (http:/ / ebindustries. com/ATLAS article. pdf)

CMS 38

CMSGeographical coordinates: 46°18′34″N 6°4′37″E

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton Synchrotron

SPS Super Proton Synchrotron

View of the CMS endcap through the barrel sections. The ladder to the lower rightgives an impression of scale.

The Compact Muon Solenoid (CMS)experiment is one of two largegeneral-purpose particle physics detectorsbuilt on the proton-proton Large HadronCollider (LHC) at CERN in Switzerland andFrance. Approximately 3,600 people from183 scientific institutes, representing 38countries form the CMS collaboration whobuilt and now operate the detector.[1] It islocated in an underground cavern at Cessyin France, just across the border fromGeneva.

Background

Recent collider experiments such as the now-dismantled Large Electron-Positron Collider at CERN and the (as of2010) still running Tevatron at Fermilab have provided remarkable insights into, and precision tests of the StandardModel of Particle Physics. However, a number of questions remain unanswered.

CMS 39

A principal concern is the lack of any direct evidence for the Higgs Boson, the particle resulting from the Higgsmechanism which provides an explanation for the masses of elementary particles. Other questions includeuncertainties in the mathematical behaviour of the Standard Model at high energies, the lack of any particle physicsexplanation for dark matter and the reasons for the imbalance of matter and antimatter observed in the Universe.The Large Hadron Collider and the associated experiments are designed to address a number of these questions.

Physics goalsThe main goals of the experiment are:• to explore physics at the TeV scale• to discover the Higgs boson• to look for evidence of physics beyond the standard model, such as supersymmetry, or extra dimensions• to study aspects of heavy ion collisionsThe ATLAS experiment, at the other side of the LHC ring is designed with similar goals in mind, and the twoexperiments are designed to complement each other both to extend reach and to provide corroboration of findings.

Detector summaryCMS is designed as a general-purpose detector, capable of studying many aspects of proton collisions at 14 TeV, thecenter-of-mass energy of the LHC particle accelerator. It contains subsystems which are designed to measure theenergy and momentum of photons, electrons, muons, and other products of the collisions. The innermost layer is asilicon-based tracker. Surrounding it is a scintillating crystal electromagnetic calorimeter, which is itself surroundedwith a sampling calorimeter for hadrons. The tracker and the calorimetry are compact enough to fit inside the CMSsolenoid which generates a powerful magnetic field of 3.8 T. Outside the magnet are the large muon detectors, whichare inside the return yoke of the magnet.

The set up of the CMS. In the middle, under the so-called barrel there is a man for scale. (HCAL=hadron calorimeter, ECAL=electromagneticcalorimeter)

CMS 40

CMS by layers

A slice of the CMS detector.

For full technical details about the CMS detector, please see the Technical Design Report [2].

The interaction pointThis is the point in the centre of the detector at which proton-proton collisions occur between the twocounter-rotating beams of the LHC. At each end of the detector magnets focus the beams into the interaction point.At collision each beam has a radius of 17 μm and the crossing angle between the beams is 285 μrad.At full design luminosity each of the two LHC beams will contain 2,808 bunches of 1.15 × 1011 protons. Theinterval between crossings is 25 ns, although the number of collisions per second is only 31.6 million due to gaps inthe beam as injector magnets are activated and deactivated.At full luminosity each collision will produce an average of 20 proton-proton interactions. The collisions occur at acentre of mass energy of 14 TeV. It is worth noting that the actual interactions occur between quarks rather thanprotons, and so the actual energy involved in each collision will be lower, as determined by the parton distributionfunctions.The first which ran in September 2008 was expected to operate at a lower collision energy of 10 TeV but this wasprevented by the 19 September 2008 shutdown. When at this target level, the LHC will have a significantly reducedluminosity, due to both fewer proton bunches in each beam and fewer protons per bunch. The reduced bunchfrequency does allow the crossing angle to be reduced to zero however, as bunches are far enough spaced to preventsecondary collisions in the experimental beampipe.

Layer 1 – The tracker

CMS 41

The silicon strip tracker of CMS.

Immediately around the interaction point the inner tracker serves toidentify the tracks of individual particles and match them to thevertices from which they originated. The curvature of charged particletracks in the magnetic field allows their charge and momentum to bemeasured.The CMS silicon tracker consists of 13 layers in the central region and14 layers in the endcaps. The innermost three layers (up to 11 cmradius) consist of 100×150 μm pixels, 66 million in total.The next four layers (up to 55 cm radius) consist of 10 cm × 180 μmsilicon strips, followed by the remaining six layers of 25 cm × 180 μmstrips, out to a radius of 1.1 m. There are 9.6 million strip channels in total.During full luminosity collisions the occupancy of the pixel layers per event is expected to be 0.1%, and 1–2% in thestrip layers. The expected SLHC upgrade will increase the number of interactions to the point where over-occupancymay significantly reduce trackfinding effectiveness.This part of the detector is the world's largest silicon detector. It has 205 m2 of silicon sensors (approximately thearea of a tennis court) comprising 76 million channels.[3]

Layer 2 – The Electromagnetic CalorimeterThe Electromagnetic Calorimeter (ECAL) is designed to measure with high accuracy the energies of electrons andphotons.The ECAL is constructed from crystals of lead tungstate, PbWO4. This is an extremely dense but optically clearmaterial, ideal for stopping high energy particles. It has a radiation length of χ0 = 0.89 cm, and has a rapid lightyield, with 80% of light yield within one crossing time (25 ns). This is balanced however by a relatively low lightyield of 30 photons per MeV of incident energy.The crystals used have a front size of 22 mm × 22 mm and a depth of 230 mm. They are set in a matrix of carbonfibre to keep them optically isolated, and backed by silicon avalanche photodiodes for readout. The barrel regionconsists of 61,200 crystals, with a further 7,324 in each of the endcaps.At the endcaps the ECAL inner surface is covered by the preshower subdetector, consisting of two layers of leadinterleaved with two layers of silicon strip detectors. Its purpose is to aid in pion-photon discrimination.

CMS 42

Preparing lead tungstate crystals for the ECAL

Layer 3 – The Hadronic Calorimeter

Half of the Hadron Calorimeter

The purpose of the Hadronic Calorimeter (HCAL) is both tomeasure the energy of individual hadrons produced in each event,and to be as near to hermetic around the interaction region aspossible to allow events with missing energy to be identified.

The HCAL consists of layers of dense material (brass or steel)interleaved with tiles of plastic scintillators, read out viawavelength-shifting fibres by hybrid photodiodes. Thiscombination was determined to allow the maximum amount ofabsorbing material inside of the magnet coil.

The high pseudorapidity region is instrumented by the Hadronic Forward detector. Located11 m either side of the interaction point, this uses a slightly different technology of steel absorbers and quartz fibresfor readout, designed to allow better separation of particles in the congested forward region.The brass used in the endcaps of the HCAL used to be Russian artillery shells.[4]

Layer 4 – The magnetLike most particle physics detectors, CMS has a large solenoid magnet. This allows the charge/mass ratio of particlesto be determined from the curved track that they follow in the magnetic field. It is 13 m long and 6 m in diameter,and its refrigerated superconducting niobium-titanium coils were originally intended to produce a 4 T magnetic field.It was recently announced that the magnet will run at 3.8 T instead of the full design strength in order to maximizelongevity.[5]

The inductance of the magnet is 14 Η and the nominal current for 4 T is 19,500 A, giving a total stored energy of 2.66 GJ, equivalent to about half-a-tonne of TNT. There are dump circuits to safely dissipate this energy should the

CMS 43

magnet quench. The circuit resistance (essentially just the cables from the power converter to the cryostat) has avalue of 0.1 mΩ which leads to a circuit time constant of nearly 39 hours. This is the longest time constant of anycircuit at CERN. The operating current for 3.8 T is 18,160 A, giving a stored energy of 2.3 GJ.

Layer 5 – The muon detectors and return yokeTo identify muons and measure their momenta, CMS uses three types of detector: drift tubes (DT), cathode stripchambers (CSC) and resistive plate chambers (RPC). The DTs are used for precise trajectory measurements in thecentral barrel region, while the CSCs are used in the end caps. The RPCs provide a fast signal when a muon passesthrough the muon detector, and are installed in both the barrel and the end caps.

The Hadron Calorimeter Barrel (in the foreground, on the yellowframe) waits to be inserted into the superconducting magnet (the silver

cylinder in the centre of the red magnet yoke).

A part of the Magnet Yoke,with drift tubes and

resistive-plate chambers inthe barrel region.

CMS 44

Collecting and collating the data

Pattern recognition

Testing the data read-out electronics for the tracker.

New particles discovered in CMS will be typically unstable andrapidly transform into a cascade of lighter, more stable and betterunderstood particles. Particles travelling through CMS leavebehind characteristic patterns, or ‘signatures’, in the differentlayers, allowing them to be identified. The presence (or not) of anynew particles can then be inferred.

Trigger system

To have a good chance of producing a rare particle, such as aHiggs boson, a very large number of collisions are required. Mostcollision events in the detector are "soft" and do not produceinteresting effects. The amount of raw data from each crossing isapproximately 1 MB, which at the 40 MHz crossing rate wouldresult in 40 TB of data a second, an amount that the experimentcannot hope to store or even process properly. The trigger systemreduces the rate of interesting events down to a manageable 100per second.

To accomplish this, a series of "trigger" stages are employed. Allthe data from each crossing is held in buffers within the detectorwhile a small amount of key information is used to perform a fast,approximate calculation to identify features of interest such as high energy jets, muons or missing energy. This"Level 1" calculation is completed in around 1 µs, and event rate is reduced by a factor of about thousand down to50 kHz. All these calculations are done on fast, custom hardware using reprogrammable FPGAs.

If an event is passed by the Level 1 trigger all the data still buffered in the detector is sent over fibre-optic links tothe "High Level" trigger, which is software (mainly written in C++) running on ordinary computer servers. Thelower event rate in the High Level trigger allows time for much more detailed analysis of the event to be done thanin the Level 1 trigger. The High Level trigger reduces the event rate by a further factor of about a thousand down toaround 100 events per second. These are then stored on tape for future analysis.

Data analysisData that has passed the triggering stages and been stored on tape is duplicated using the Grid to additional sitesaround the world for easier access and redundancy. Physicists are then able to use the Grid to access and run theiranalyses on the data.Some possible analyses might be:• Looking at events with large amounts of apparently missing energy, which implies the presence of particles that

have passed through the detector without leaving a signature, such as neutrinos.• Looking at the kinematics of pairs of particles produced by the decay of a parent, such as the Z boson decaying to

a pair of electrons or the Higgs boson decaying to a pair of tau leptons or photons, to determine the properties andmass of the parent.

• Looking at jets of particles to study the way the quarks in the collided protons have interacted.

CMS 45

Milestones

1998 Construction of surface buildings for CMS begins.

2000 LEP shut down, construction of cavern begins.

2004 Cavern completed.

10 September 2008 First beam in CMS.

23 November 2009 First collisions in CMS.

30 March 2010 First 7 TeV collisions in CMS.

The insertion of the vacuum tank,June 2002

YE+2 descent into the cavern YE+1, a component of CMSweighing 1,270 tonnes, finishesits 100 m descent into the CMS

cavern, January 2007

Computer-generated eventdisplay of protons hitting a

tungsten block just upstreamof CMS on the first beam

day, September 2008

References[1] (http:/ / cms-project-cmsinfo. web. cern. ch/ cms-project-cmsinfo/ Collaboration/ index. html)[2] http:/ / cdsweb. cern. ch/ record/ 922757/ files/ lhcc-2006-001. pdf[3] CMS installs the world's largest silicon detector (http:/ / cerncourier. com/ cws/ article/ cern/ 32915), CERN Courier, Feb 15, 2008[4] CMS HCAL history - CERN (http:/ / cms. web. cern. ch/ cms/ Detector/ HCAL/ History. html)[5] http:/ / iopscience. iop. org/ 1748-0221/ 5/ 03/ T03021/ pdf/ 1748-0221_5_03_T03021. pdf Precise mapping of the magnetic field in the CMS

barrel yoke using cosmic rays

• Della Negra, Michel; Petrilli, Achille; Herve, Alain; Foa, Lorenzo; (2006) (PDF). CMS Physics Technical DesignReport Volume I: Software and Detector Performance (http:/ / doc. cern. ch/ / archive/ electronic/ cern/ preprints/lhcc/ public/ lhcc-2006-001. pdf). CERN.

External links• CMS home page (http:/ / cms. cern. ch/ )• CMS Outreach (http:/ / cmsinfo. cern. ch/ )• CMS Times (http:/ / cmsinfo. cern. ch/ outreach/ CMSTimes. html)• CMS section from US/LHC Website (http:/ / www. uslhc. us/ What_is_the_LHC/ Experiments/ CMS)• http:/ / petermccready. com/ portfolio/ 07041601. html (http:/ / petermccready. com/ portfolio/ 07041601. html)

Panoramic view - click and drag to look around the experiment under construction (with sound!) (requiresQuicktime)

• The assembly of the CMS detector, step by step, through a 3D animation (http:/ / www. youtube. com/watch?v=7FiLC2m4oR8)

• The CMS Collaboration, S Chatrchyan et al. (2008-08-14). "The CMS experiment at the CERN LHC" (http:/ /www. iop. org/ EJ/ journal/ -page=extra. lhc/ jinst). Journal of Instrumentation 3: S08004.doi:10.1088/1748-0221/3/08/S08004. Retrieved 2008-08-26 (Full design documentation)

LHCb 46

LHCbGeographical coordinates: 46°14′27.64″N 6°5′48.96″E

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton Synchrotron

SPS Super Proton Synchrotron

The LHCb (standing for "Large Hadron Collider beauty" where "beauty" refers to the bottom quark) experiment isone of six particle physics detector experiments built on the Large Hadron Collider accelerator at CERN. LHCb is aspecialized b-physics experiment, particularly aimed at measuring the parameters of CP violation in the interactionsof b-hadrons (heavy particles containing a bottom quark).

The LHCb detectorThe fact that b-hadrons are predominantly produced in the same forward cone as B meson production is exploited inthe layout of the LHCb detector. The LHCb detector is a single arm forward spectrometer with a polar angularcoverage from 10 to 300 milliradians (mrad) in the horizontal and 250 mrad in the vertical plane. The asymmetrybetween the horizontal and vertical plane is determined by a large dipole magnet with the main component in thevertical direction.The vertex detector (known as the vertex locator or VELO) is built around the proton interaction region. It is used tomeasure the particle trajectories close to the interaction point in order to precisely separate primary and secondaryvertices, e.g. for B-tagging.The RICH-1 detector (Ring imaging Cherenkov detector) is located directly after the vertex detector. It is used forparticle identification of low-momentum tracks.The main tracking system is placed before and after the dipole magnet. It is used to reconstruct the trajectories ofcharged particles and to measure their momenta.

LHCb 47

Following the tracking system is RICH-2. It allows the identification of the particle type of high-momentum tracks.The electromagnetic and hadronic calorimeters provide measurement of the energy of electrons, photons, andhadrons. These measurements are used at trigger level to identify the particles with high transversal moment (high-Ptparticles).The muon system is used to identify and trigger on muons in the events.

LHCb Physics analysesAfter the LHC starts colliding protons at a useful rate for LHCb, in early 2010, LHCb aims to make severalmeasurements on physics phenomena involving B mesons as an early priority. These include:

• Measuring an upper limit on the branching ratio of the rare decay.• Measuring the forward-backward asymmetry of the muon pair in the flavour changing neutral current

decay. Such a flavour changing neutral current cannot occur at tree-level in the StandardModel of Particle Physics, and only occurs through box and loop Feynman diagrams; properties of the decay canbe strongly modified by new Physics.

• Measuring the CP violating phase in the decay , caused by interference between the decays withand without oscillations. This phase is one of the CP observables with the smallest theoreticaluncertainty in the Standard Model, and can be significantly modified by new Physics.

• Measuring properties of radiative B decays, i.e. B meson decays with photons in the final states. Specifically,these are again flavour changing neutral current decays.

LHCb 48

External links• LHCb Public Webpage [1]

• LHCb section from US/LHC Website [2]

• A. Augusto Alves Jr. et al. (LHCb Collaboration) (2008). "The LHCb Detector at the LHC" [5]. Journal ofInstrumentation 3: S08005. doi:10.1088/1748-0221/3/08/S08005. (Full design documentation)

References[1] http:/ / lhcb-public. web. cern. ch/ lhcb-public/[2] http:/ / www. uslhc. us/ What_is_the_LHC/ Experiments/ LHCb

LHCf 49

LHCf

The LHCf experiment, the smallest of the sixexperiments on the LHC

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton Synchrotron

SPS Super Proton Synchrotron

The LHCf ("Large Hadron Collider forward") is a special-purpose Large Hadron Collider experiment forastroparticle (cosmic ray) physics, and one of six detectors in the LHC accelerator at CERN. The other five are:ATLAS, ALICE, CMS, TOTEM, and LHCb. LHCf is designed to study the particles generated in the "forward"region of collisions, those almost directly in line with the colliding proton beams. It therefore consists of twodetectors, 140 m on either side of an intersection point.Because of this large distance, it can co-exist with a more conventional detector surrounding the intersection point,and shares the intersection point IP1 with the much larger general-purpose ATLAS experiment.

LHCf 50

PurposeThe LHCf is intended to measure the energy and numbers of neutral pions (π0) produced by the collider. This willhopefully help explain the origin of ultra-high-energy cosmic rays. The results will complement other high-energycosmic ray measurements from the Pierre Auger Observatory in Argentina, and the Telescope Array in Utah.

References• LHCf section on US/LHC Website [1]

• LHCf: a tiny new experiment joins the LHC [2], CERN Courier, Nov 1, 2006, retrieved on 2009-03-25.(Describes the location of the experiment.)

• The LHCf experiment at LHC [3]

• Technical Design Report of LHCf [4]

• O Adriani et al. (LHCf Collaboration) (2008). "The LHCf detector at the CERN Large Hadron Collider". Journalof Instrumentation 3 (8): S08006. doi:10.1088/1748-0221/3/08/S08006. (Full design documentation)

Geographical coordinates: 46°14′09″N 6°03′18″E

References[1] http:/ / www. uslhc. us/ What_is_the_LHC/ Experiments/ LHCf[2] http:/ / cerncourier. com/ cws/ article/ cern/ 29732[3] http:/ / www. particle. cz/ conferences/ c2cr2005/ talks/ Adriani. pdf[4] http:/ / doc. cern. ch/ / archive/ electronic/ cern/ preprints/ lhcc/ public/ lhcc-2005-032. pdf

FP420The FP420 R&D project or the FP420 experiment was an international collaboration with members from 29institutes from 10 countries.[1] The aim was to assess the feasibility of installing proton tagging detectors at 420 mfrom the interaction points of the ATLAS and CMS experiments at the Large Hadron Collider (LHC). One of themost notable members of the team was Brian Cox, who can be seen in the five part BBC television series entitledWonders of the Solar System which first aired in March 2010.By detecting protons that have lost less than 1% of their longitudinal momentum, it is possible to obtain informationthat could yield insight on various phenomena of high-energy physics. These measurements would be unique at theLHC, and would be difficult to obtain at both existing and future linear colliders.

References[1] "FP420 R&D Project" (http:/ / www. fp420. com/ ). . Retrieved 2010-03-31.

External links• FP420 R&D Project website (http:/ / www. fp420. com/ )• Papers and Reviews (http:/ / www. fp420. com/ papers. html)

TOTEM 51

TOTEM

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton Synchrotron

SPS Super Proton Synchrotron

TOTal Elastic and diffractive cross section Measurement (TOTEM) is one of the six detector experiments at theLarge Hadron Collider at CERN. The other five are: ATLAS, ALICE, CMS, LHCb, and LHCf. It shares intersectionpoint IP5 with the Compact Muon Solenoid. The detector aims at measurement of total cross section, elasticscattering and diffractive processes.

External links• TOTEM Public Webpage [1]

• TOTEM section on US/LHC Website [2]

• The TOTEM Collaboration, G Anelli et al. (2008-08-14), "The TOTEM Experiment at the CERN Large HadronCollider" [5], Journal of Instrumentation 3 (S08007): S08007, doi:10.1088/1748-0221/3/08/S08007, retrieved2008-08-26 (Full design documentation)

Geographical coordinates: 46°18′35″N 6°04′35″E

TOTEM 52

References[1] http:/ / totem. web. cern. ch/ Totem[2] http:/ / www. uslhc. us/ What_is_the_LHC/ Experiments/ TOTEM

53

Technology

Beetle ASIC

Beetle chip

The Beetle ASIC is an analog readout chip. It is developed for theLHCb experiment at CERN.

Overview

The chip integrates 128 channels with low-noise charge-sensitivepre-amplifiers and shapers. The pulse shape can be chosen suchthat it complies with LHCb specifications: a peaking time of 25 nswith a remainder of the peak voltage after 25 ns of less than 30%.A comparator per channel with configurable polarity provides abinary signal. Four adjacent comparator channels are being ORedand brought off chip via LVDS drivers.

Either the shaper or comparator output is sampled with the LHC bunch-crossing frequency of 40 MHz into an analogpipeline. This ring buffer has a programmable latency of a maximum of 160 sampling intervals and an integratedderandomising buffer of 16 stages. For analogue readout data is multiplexed with up to 40 MHz onto one or fourports. A binary readout mode operates at up to 80 MHz output rate on two ports. Current drivers bring the serialiseddata off chip.The chip can accept trigger rates up to 1.1 MHz to perform a dead-timeless readout within 900 ns per trigger. Fortestability and calibration purposes, a charge injector with adjustable pulse height is implemented. The bias settingsand various other parameters can be controlled via a standard I²C-interface. The chip is radiation hardened to anaccumulated dose of more than 100 Mrad. Robustness against single event upset is achieved by redundant logic.

External links• Beetle - a readout chip for LHCb [1]

• The Large Hadron Collider beauty experiment [13]

References[1] http:/ / wwwasic. kip. uni-heidelberg. de/ lhcb

LHC Computing Grid 54

LHC Computing GridThe LHC Computing Grid, launched on October 3, 2008,[1] is a distribution network designed by CERN to handlethe massive amounts of data produced by the Large Hadron Collider (LHC). It incorporates both private fiber opticcable links and existing high-speed portions of the public Internet.The data stream from the detectors provides approximately 300 GB/s, which is filtered for "interesting events",resulting in a "raw data" stream of about 300 MB/s. The CERN computer center, considered "Tier 0" of the LHCComputing Grid, has a dedicated 10 Gb/s connection to the counting room.[2]

The project is expected to generate 27 TB of raw data per day, plus 10 TB of “event summary data”, which representsthe output of calculations done by the CPU farm at the CERN data center.[2] This data is sent out from CERN toeleven Tier 1 academic institutions in Europe, Asia, and North America, via dedicated 10 Gbit/s links. More than150 Tier 2 institutions are connected to the Tier 1 institutions by general-purpose national research and educationnetworks.[2] The data produced by the LHC on all of its distributed computing grid is expected to add up to 10–15PB of data each year.[3]

The Tier 1 institutions receive specific subsets of the raw data, for which they serve as a backup repository forCERN. They also perform reprocessing when recalibration is necessary.[2] The primary configuration for thecomputers used in the grid is based on Scientific Linux.Distributed computing resources for analysis by end-user physicists are provided by the Open Science Grid,Enabling Grids for E-sciencE,[2] and LHC@home projects.

See also• Openlab (CERN)

References[1] "LHC GridFest" (http:/ / lcg. web. cern. ch/ LCG/ lhcgridfest/ ). CERN. 2008. .[2] final-draft-4-key (http:/ / gridcafe. web. cern. ch/ gridcafe/ animations/ LHCdata/ LHCdata. html)[3] Brodkin, Jon (28 April 2008). "Parallel Internet: Inside the Worldwide LHC computing grid" (http:/ / www. techworld. com/ mobility/

features/ index. cfm?featureid=4074& pn=2). Techworld.com. .

External links• Official webpage (http:/ / lcg. web. cern. ch/ LCG/ ) The World Wide LHC Computer Grid

LHC@home 55

LHC@homeLHC@home is a distributed computing project using the BOINC framework, run by volunteers on behalf of theEuropean Organization for Nuclear Research (CERN). Its primary goal is to help maintain and improve the LargeHadron Collider (LHC), which became active in September 2008. Data from the project is utilized by engineers toimprove the operation and efficiency of the accelerator, and to predict possible problems that could arise fromadjustment or modification of the LHC's equipment. The project is administered by volunteers, and receives nofunding from CERN.BOINC users who are considering joining this project should know that it only occasionally has work; the project isused for design and repair considerations related to the LHC. There are currently no plans to use the project to docomputation on the data that will be collected by the LHC.

A CERN collider projectThe project was first introduced as a beta on September 1, 2004 and a record 1000 users signed up within 24 hours.The project went public, with a 5000 user limit, on September 29 to commemorate CERN's 50th anniversary.Currently there is no user limit and qualification.

Project softwareThe project software involves a program called "SixTrack", created by Frank Schmidt, downloaded via BOINC ontoparticipant computers running Windows or Linux. SixTrack simulates particles accelerating through the 27 km (17mi)-long LHC to find their orbit stability.• In one workunit, 60 particles are simulated travelling 100,000 or 1,000,000 loops, which would take about 10

seconds in an actual run. This is sixtrack.• The orbit stability data is used to detect if a particle in orbit goes off-course and runs into the tube wall—if this

happened too often in actual running, this would cause damage to the accelerator which would need repairs.• A new experimental version called SixTrackbnl started to be sent to computers in early November.• Garfield is a newer application, although not many workunits have been seen lately.

See also• List of distributed computing projects• LHC Computing Grid

External links• LHC@home Project Page [1]

• Berkeley Open Infrastructure for Network Computing (BOINC) [2]

• SixTrack homepage [3]

LHC@home 56

References[1] http:/ / lhcathome. cern. ch/[2] http:/ / boinc. berkeley. edu/[3] http:/ / frs. web. cern. ch/ frs/

Proton Synchrotron BoosterThe Proton Synchrotron Booster, a synchrotron, is the first and smallest circular proton accelerator in theaccelerator chain at the CERN Large Hadron Collider injection complex[1]. The accelerator was built in 1972, andcontains four superimposed rings with a radius of 25 meters. It takes protons with an energy of 50 MeV from thelinear accelerator Linac2 and accelerates them up to 1.4 GeV, ready to be injected into the Proton Synchrotron. It canalso take ions from the Linac3 pre-accelerated in the LEIR.The PS Booster actually consists of four identical rings mounted one above the other.

External links• PS Booster Machine: layout and photographs [2]

References[1] http:/ / ps-div. web. cern. ch/ ps-div/ LHC-PS/ LHC-PS. html[2] http:/ / psb-machine. web. cern. ch/ psb-machine/

VELOThe Vertex Locator at LHCb is called the VELO. Its primary purpose is to provide high precision measurements ofthe tracks of charged particles resulting from pp collisions at the LHC.The detector operates at 7 mm from the LHC beam. This implies an enormous flux of particles; thus the VELO hasbeen designed to withstand integrated fluences of more than 1014p/cm2 per year for a period of about three years.The detector operates in vacuum and is cooled to approximately −25 °C using a biphase CO2 system. The data of theVELO detector are amplified and read out by the Beetle ASIC.The VELO provides critical tracking information for the LHCb experiment.

References• The LHCb VELO (from the VELO group) [1]

• VELO Public Pages(from the LHCb experiment) [2]

References[1] http:/ / lhcb-vd. web. cern. ch/ lhcb-vd/ default. htm[2] http:/ / lhcb-public. web. cern. ch/ lhcb-public/ en/ Detector/ VELO-en. html

57

Theory

Standard Model

The Standard Model of elementary particles, with the gauge bosons in therightmost column.

The standard model of particle physics is atheory concerning the electromagnetic,weak, and strong nuclear interactions, whichmediate the dynamics of the knownsubatomic particles. Developed throughoutthe early and middle 20th century, thecurrent formulation was finalized in the mid1970s upon experimental confirmation ofthe existence of quarks. Since then,discoveries of the bottom quark (1977), thetop quark (1995) and the tau neutrino (2000)have given credence to the standard model.Because of its success in explaining a widevariety of experimental results, the standardmodel is sometimes regarded as a theory ofalmost everything.

Still, the standard model falls short of beinga complete theory of fundamentalinteractions because it does not incorporatethe physics of general relativity, such asgravitation and dark energy. The theorydoes not contain any viable dark matterparticle that possesses all of the required properties deduced from observational cosmology. It also does not correctlyaccount for neutrino oscillations (and their non-zero masses). Although the standard model is theoreticallyself-consistent, it has several unnatural properties giving rise to puzzles like the strong CP problem and the hierarchyproblem.

Nevertheless, the standard model is important to theoretical and experimental particle physicists alike. Fortheoreticians, the standard model is a paradigm example of a quantum field theory, which exhibits a wide range ofphysics including spontaneous symmetry breaking, anomalies, non-perturbative behavior, etc. It is used as a basis forbuilding more exotic models which incorporate hypothetical particles, extra dimensions and elaborate symmetries(such as supersymmetry) in an attempt to explain experimental results at variance with the standard model such asthe existence of dark matter and neutrino oscillations. In turn, the experimenters have incorporated the standardmodel into simulators to help search for new physics beyond the standard model from relatively uninterestingbackground.Recently, the standard model has found applications in other fields besides particle physics such as astrophysics andcosmology, in addition to nuclear physics.

Standard Model 58

Historical backgroundThe first step towards the Standard Model was Sheldon Glashow's discovery, in 1960, of a way to combine theelectromagnetic and weak interactions.[1] In 1967, Steven Weinberg[2] and Abdus Salam[3] incorporated the Higgsmechanism[4] [5] [6] into Glashow's electroweak theory, giving it its modern form.The Higgs mechanism is believed to give rise to the masses of all the elementary particles in the Standard Model.This includes the masses of the W and Z bosons, and the masses of the fermions - i.e. the quarks and leptons.After the neutral weak currents caused by Z boson exchange were discovered at CERN in 1973,[7] [8] [9] [10] theelectroweak theory became widely accepted and Glashow, Salam, and Weinberg shared the 1979 Nobel Prize inPhysics for discovering it. The W and Z bosons were discovered experimentally in 1981, and their masses werefound to be as the Standard Model predicted.The theory of the strong interaction, to which many contributed, acquired its modern form around 1973–74, whenexperiments confirmed that the hadrons were composed of fractionally charged quarks.

OverviewAt present, matter and energy are best understood in terms of the kinematics and interactions of elementary particles.To date, physics has reduced the laws governing the behavior and interaction of all known forms of matter andenergy to a small set of fundamental laws and theories. A major goal of physics is to find the "common ground" thatwould unite all of these theories into one integrated theory of everything, of which all the other known laws wouldbe special cases, and from which the behavior of all matter and energy could be derived (at least in principle).[11]

The Standard Model groups two major extant theories—quantum electroweak and quantum chromodynamics—intoan internally consistent theory that describes the interactions between all known particles in terms of quantum fieldtheory. For a technical description of the fields and their interactions, see Standard Model (mathematicalformulation).

Particle content

Fermions

Organization of Fermions

Charge First generation Second generation Third generation

Quarks +2⁄3Up u Charm c Top t

−1⁄3Down d Strange s Bottom b

Leptons −1 Electron e− Muon μ− Tau τ−

0 Electron neutrino νe Muon neutrino νμ Tau neutrino ντ

The Standard Model includes 12 elementary particles of spin-1⁄2 known as fermions. According to the spin-statisticstheorem, fermions respect the Pauli exclusion principle. Each fermion has a corresponding antiparticle.The fermions of the Standard Model are classified according to how they interact (or equivalently, by what chargesthey carry). There are six quarks (up, down, charm, strange, top, bottom), and six leptons (electron, electronneutrino, muon, muon neutrino, tau, tau neutrino). Pairs from each classification are grouped together to form ageneration, with corresponding particles exhibiting similar physical behavior (see table).The defining property of the quarks is that they carry color charge, and hence, interact via the strong interaction. A phenomenon called color confinement results in quarks being perpetually (or at least since very soon after the start of

Standard Model 59

the Big Bang) bound to one another, forming color-neutral composite particles (hadrons) containing either a quarkand an antiquark (mesons) or three quarks (baryons). The familiar proton and the neutron are the two baryons havingthe smallest mass. Quarks also carry electric charge and weak isospin. Hence they interact with other fermions bothelectromagnetically and via the weak nuclear interaction.The remaining six fermions do not carry color charge and are called leptons. The three neutrinos do not carry electriccharge either, so their motion is directly influenced only by the weak nuclear force, which makes them notoriouslydifficult to detect. However, by virtue of carrying an electric charge, the electron, muon, and tau all interactelectromagnetically.Each member of a generation has greater mass than the corresponding particles of lower generations. The firstgeneration charged particles do not decay; hence all ordinary (baryonic) matter is made of such particles.Specifically, all atoms consist of electrons orbiting atomic nuclei ultimately constituted of up and down quarks.Second and third generations charged particles, on the other hand, decay with very short half lives, and are observedonly in very high-energy environments. Neutrinos of all generations also do not decay, and pervade the universe, butrarely interact with baryonic matter.

Gauge bosons

Summary of interactions between particles described by the Standard Model.

In the Standard Model, gauge bosonsare force carriers that mediate thestrong, weak, and electromagneticfundamental interactions.

Interactions in physics are the waysthat particles influence other particles.At a macroscopic level,electromagnetism allows particles tointeract with one another via electricfield and magnetic fields, andgravitation allows particles with massto attract one another in accordancewith Einstein's general relativity. Thestandard model explains such forces asresulting from matter particlesexchanging other particles, known asforce mediating particles (Strictly speaking, this is only so if interpreting literally what is actually an approximationmethod known as perturbation theory, as opposed to the exact theory). When a force mediating particle is exchanged,at a macroscopic level the effect is equivalent to a force influencing both of them, and the particle is therefore said tohave mediated (i.e., been the agent of) that force. The Feynman diagram calculations, which are a graphical form ofthe perturbation theory approximation, invoke "force mediating particles" and when applied to analyze high-energyscattering experiments are in reasonable agreement with the data. Perturbation theory (and with it the concept of"force mediating particle") in other situations fails. These include low-energy QCD, bound states, and solitons.

The gauge bosons of the Standard Model also all have spin(as do matter particles), but in their case, the value of thespin is 1, making them bosons. As a result, they do not follow the Pauli exclusion principle as leptons do, andtherefore bosons (e.g. photons) do not have a theoretical limit on their spatial density (number per volume). Thedifferent types of gauge bosons are described below.• Photons mediate the electromagnetic force between electrically charged particles. The photon is massless and is

well-described by the theory of quantum electrodynamics.

Standard Model 60

• The W+, W−, and Z gauge bosons mediate the weak interactions between particles of different flavors (all quarksand leptons). They are massive, with the Z being more massive than the W±. The weak interactions involving theW± act on exclusively left-handed particles and right-handed antiparticles. Furthermore, the W± carry an electriccharge of +1 and −1 and couple to the electromagnetic interactions. The electrically neutral Z boson interacts withboth left-handed particles and antiparticles. These three gauge bosons along with the photons are grouped togetherwhich collectively mediate the electroweak interactions.

• The eight gluons mediate the strong interactions between color charged particles (the quarks). Gluons aremassless. The eightfold multiplicity of gluons is labeled by a combination of color and an anticolor charge (e.g.,red–antigreen).[12] Because the gluon has an effective color charge, they can interact among themselves. Thegluons and their interactions are described by the theory of quantum chromodynamics.

The interactions between all the particles described by the Standard Model are summarized by the diagram at the topof this section.

Higgs bosonThe Higgs particle is a hypothetical massive scalar elementary particle theorized by Robert Brout, François Englert,Peter Higgs, Gerald Guralnik, C. R. Hagen, and Tom Kibble in 1964 (see 1964 PRL symmetry breaking papers) andis a key building block in the Standard Model.[13] [14] [15] [16] It has no intrinsic spin, and for that reason is classifiedas a boson (like the gauge bosons, which have integer spin). Because an exceptionally large amount of energy andbeam luminosity are theoretically required to observe a Higgs boson in high energy colliders, it is the onlyfundamental particle predicted by the Standard Model that has yet to be observed.The Higgs boson plays a unique role in the Standard Model, by explaining why the other elementary particles, thephoton and gluon excepted, are massive. In particular, the Higgs boson would explain why the photon has no mass,while the W and Z bosons are very heavy. Elementary particle masses, and the differences betweenelectromagnetism (mediated by the photon) and the weak force (mediated by the W and Z bosons), are critical tomany aspects of the structure of microscopic (and hence macroscopic) matter. In electroweak theory, the Higgsboson generates the masses of the leptons (electron, muon, and tau) and quarks.As yet, no experiment has directly detected the existence of the Higgs boson. It is hoped that the Large HadronCollider at CERN will confirm the existence of this particle. It is also possible that the Higgs boson may alreadyhave been produced but overlooked.[17]

Field contentThe standard model has the following fields:

Spin 11. A U(1) gauge field Bμν with coupling g′ (weak U(1), or weak hypercharge)2. An SU(2) gauge field Wμν with coupling g (weak SU(2), or weak isospin)3. An SU(3) gauge field Gμν with coupling gs (strong SU(3), or color charge)

Spin 1⁄2The spin 1⁄2 particles are in representations of the gauge groups. For the U(1) group, we list the value of the weakhypercharge instead. The left-handed fermionic fields are:1. An SU(3) triplet, SU(2) doublet, with U(1) weak hypercharge 1⁄3 (left-handed quarks)2. An SU(3) triplet, SU(2) singlet, with U(1) weak hypercharge 2⁄3 (left-handed down-type antiquark)3. An SU(3) singlet, SU(2) doublet with U(1) weak hypercharge −1 (left-handed lepton)4. An SU(3) triplet, SU(2) singlet, with U(1) weak hypercharge −4⁄3 (left-handed up-type antiquark)

Standard Model 61

5. An SU(3) singlet, SU(2) singlet with U(1) weak hypercharge 2 (left-handed antilepton)By CPT symmetry, there is a set of right-handed fermions with the opposite quantum numbers.This describes one generation of leptons and quarks, and there are three generations, so there are three copies of eachfield. Note that there are twice as many left-handed lepton field components as left-handed antilepton fieldcomponents in each generation, but an equal number of left-handed quark and antiquark fields.

Spin 01. An SU(2) doublet H with U(1) hyper-charge −1 (Higgs field)Note that |H|2, summed over the two SU(2) components, is invariant under both SU(2) and under U(1), and so it canappear as a renormalizable term in the Lagrangian, as can its square.This field acquires a vacuum expectation value, leaving a combination of the weak isospin, I3, and weak hyperchargeunbroken. This is the electromagnetic gauge group, and the photon remains massless. The standard formula for theelectric charge (which defines the normalization of the weak hypercharge, Y, which would otherwise be somewhatarbitrary) is:[18]

LagrangianThe Lagrangian for the spin 1 and spin 1⁄2 fields is the most general renormalizable gauge field Lagrangian with nofine tunings:• Spin 1:

where the traces are over the SU(2) and SU(3) indices hidden in W and G respectively. The two-index objects are thefield strengths derived from W and G the vector fields. There are also two extra hidden parameters: the theta anglesfor SU(2) and SU(3).The spin-1⁄2 particles can have no mass terms because there is no right/left helicity pair with the same SU(2) andSU(3) representation and the same weak hypercharge. This means that if the gauge charges were conserved in thevacuum, none of the spin 1⁄2 particles could ever swap helicity, and they would all be massless.For a neutral fermion, for example a hypothetical right-handed lepton N (or Nα in relativistic two-spinor notation),with no SU(3), SU(2) representation and zero charge, it is possible to add the term:

This term gives the neutral fermion a Majorana mass. Since the generic value for M will be of order 1, such a particlewould generically be unacceptably heavy. The interactions are completely determined by the theory – the leptonsintroduce no extra parameters.

Standard Model 62

Higgs mechanismThe Lagrangian for the Higgs includes the most general renormalizable self interaction:

The parameter v2 has dimensions of mass squared, and it gives the location where the classical Lagrangian is at aminimum. In order for the Higgs mechanism to work, v2 must be a positive number. v has units of mass, and it is theonly parameter in the standard model which is not dimensionless. It is also much smaller than the Planck scale; it isapproximately equal to the Higgs mass, and sets the scale for the mass of everything else. This is the only realfine-tuning to a small nonzero value in the standard model, and it is called the Hierarchy problem.It is traditional to choose the SU(2) gauge so that the Higgs doublet in the vacuum has expectation value (v,0).

Masses and CKM matrixThe rest of the interactions are the most general spin-0 spin-1⁄2 Yukawa interactions, and there are many of these.These constitute most of the free parameters in the model. The Yukawa couplings generate the masses and mixingsonce the Higgs gets its vacuum expectation value.The terms L*HR generate a mass term for each of the three generations of leptons. There are 9 of these terms, but byrelabeling L and R, the matrix can be diagonalized. Since only the upper component of H is nonzero, the upperSU(2) component of L mixes with R to make the electron, the muon, and the tau, leaving over a lower masslesscomponent, the neutrino. {Neutrino oscillation show neutrinos have mass. http:/ / operaweb. lngs. infn. it/ spip.php?rubrique14 31May2010 Press Release.}The terms QHU generate up masses, while QHD generate down masses. But since there is more than oneright-handed singlet in each generation, it is not possible to diagonalize both with a good basis for the fields, andthere is an extra CKM matrix.

Theoretical aspects

Construction of the Standard Model Lagrangian

Parameters of the Standard Model

Symbol Description Renormalizationscheme (point)

Value

me Electron mass 511 keV

mμ Muon mass 105.7 MeV

mτ Tau mass 1.78 GeV

mu Up quark mass μMS = 2 GeV 1.9 MeV

md Down quark mass μMS = 2 GeV 4.4 MeV

ms Strange quark mass μMS = 2 GeV 87 MeV

mc Charm quark mass μMS = mc 1.32 GeV

mb Bottom quark mass μMS = mb 4.24 GeV

mt Top quark mass On-shell scheme 172.7 GeV

θ12 CKM 12-mixing angle 13.1°

θ23 CKM 23-mixing angle 2.4°

θ13 CKM 13-mixing angle 0.2°

Standard Model 63

δ CKM CP-violating Phase 0.995

g1 U(1) gauge coupling μMS = mZ 0.357

g2 SU(2) gauge coupling μMS = mZ 0.652

g3 SU(3) gauge coupling μMS = mZ 1.221

θQCD QCD vacuum angle ~0

μ Higgs quadratic coupling Unknown

λ Higgs self-coupling strength Unknown

Technically, quantum field theory provides the mathematical framework for the standard model, in which aLagrangian controls the dynamics and kinematics of the theory. Each kind of particle is described in terms of adynamical field that pervades space-time. The construction of the standard model proceeds following the modernmethod of constructing most field theories: by first postulating a set of symmetries of the system, and then by writingdown the most general renormalizable Lagrangian from its particle (field) content that observes these symmetries.The global Poincaré symmetry is postulated for all relativistic quantum field theories. It consists of the familiartranslational symmetry, rotational symmetry and the inertial reference frame invariance central to the theory ofspecial relativity. The local SU(3)×SU(2)×U(1) gauge symmetry is an internal symmetry that essentially defines thestandard model. Roughly, the three factors of the gauge symmetry give rise to the three fundamental interactions.The fields fall into different representations of the various symmetry groups of the Standard Model (see table). Uponwriting the most general Lagrangian, one finds that the dynamics depend on 19 parameters, whose numerical valuesare established by experiment. The parameters are summarized in the table at right.

The QCD sector

The QCD sector defines the interactions between quarks and gluons, with SU(3) symmetry, generated by Ta. Sinceleptons do not interact with gluons, they are not affected by this sector.

is the gluon field strength, are the Dirac matrices, D stands for the isospin doublet section, U stands for aunitary matrix, and gs is the strong coupling constant.

The electroweak sector

The electroweak sector is a Yang–Mills gauge theory with the symmetry group U(1)×SU(2)L,

where Bμ is the U(1) gauge field; YW is the weak hypercharge—the generator of the U(1) group; is the

three-component SU(2) gauge field; are the Pauli matrices—infinitesimal generators of the SU(2) group. Thesubscript L indicates that they only act on left fermions; g′ and g are coupling constants.

Standard Model 64

The Higgs sector

In the Standard Model, the Higgs field is a complex spinor of the group SU(2)L:

where the indexes + and 0 indicate the electric charge (Q) of the components. The weak isospin (YW) of bothcomponents is 1.Before symmetry breaking, the Higgs Lagrangian is:

which can also be written as:

Additional symmetries of the Standard ModelFrom the theoretical point of view, the Standard Model exhibits four additional global symmetries, not postulated atthe outset of its construction, collectively denoted accidental symmetries, which are continuous U(1) globalsymmetries. The transformations leaving the Lagrangian invariant are:

The first transformation rule is shorthand meaning that all quark fields for all generations must be rotated by anidentical phase simultaneously. The fields , and , are the 2nd (muon) and 3rd (tau)generation analogs of and fields.By Noether's theorem, each symmetry above has an associated conservation law: the conservation of baryon number,electron number, muon number, and tau number. Each quark is assigned a baryon number of 1/3, while eachantiquark is assigned a baryon number of -1/3. Conservation of baryon number implies that the number of quarksminus the number of antiquarks is a constant. Within experimental limits, no violation of this conservation law hasbeen found.Similarly, each electron and its associated neutrino is assigned an electron number of +1, while the antielectron andthe associated antineutrino carry −1 electron number. Similarly, the muons and their neutrinos are assigned a muonnumber of +1 and the tau leptons are assigned a tau lepton number of +1. The Standard Model predicts that each ofthese three numbers should be conserved separately in a manner similar to the way baryon number is conserved.These numbers are collectively known as lepton family numbers (LF). Symmetry works differently for quarks thanfor leptons, mainly because the Standard Model predicts that neutrinos are massless. However, it was recently foundthat neutrinos have small masses and oscillate between flavors, signaling that the conservation of lepton familynumber is violated.In addition to the accidental (but exact) symmetries described above, the Standard Model exhibits severalapproximate symmetries. These are the "SU(2) custodial symmetry" and the "SU(2) or SU(3) quark flavorsymmetry."

Standard Model 65

Symmetries of the Standard Model and Associated Conservation Laws

Symmetry Lie Group Symmetry Type Conservation Law

Poincaré Translations×SO(3,1) Global symmetry Energy, Momentum, Angular momentum

Gauge SU(3)×SU(2)×U(1) Local symmetry Color charge, Weak isospin, Electric charge, Weak hypercharge

Baryon phase U(1) Accidental Global symmetry Baryon number

Electron phase U(1) Accidental Global symmetry Electron number

Muon phase U(1) Accidental Global symmetry Muon number

Tau phase U(1) Accidental Global symmetry Tau number

Field content of the Standard Model

Field(1st generation)

Spin Gauge groupRepresentation

BaryonNumber

ElectronNumber

Left-handed quark ( , , )

Left-handed up antiquark ( , , )

Left-handed down antiquark ( , , )

Left-handed lepton ( , , )

Left-handed antielectron ( , , )

Hypercharge gauge field ( , , )

Isospin gauge field ( , , )

Gluon field ( , , )

Higgs field ( , , )

List of standard model fermionsThis table is based in part on data gathered by the Particle Data Group.[19]

Left-handed fermions in the Standard Model

Generation 1

Fermion(left-handed)

Symbol Electriccharge

Weakisospin

Weakhypercharge

Colorcharge *

Mass **

Electron 511 keV

Positron 511 keV

Electron neutrino < 2 eV ****

Electron antineutrino < 2 eV ****

Up quark ~ 3 MeV ***

Up antiquark ~ 3 MeV ***

Down quark ~ 6 MeV ***

Down antiquark ~ 6 MeV ***

Generation 2

Standard Model 66

Fermion(left-handed)

Symbol Electriccharge

Weakisospin

Weakhypercharge

Colorcharge *

Mass **

Muon 106 MeV

Antimuon 106 MeV

Muon neutrino < 2 eV ****

Muon antineutrino < 2 eV ****

Charm quark ~ 1.337 GeV

Charm antiquark ~ 1.3 GeV

Strange quark ~ 100 MeV

Strange antiquark ~ 100 MeV

Generation 3

Fermion(left-handed)

Symbol Electriccharge

Weakisospin

Weakhypercharge

Colorcharge *

Mass **

Tau 1.78 GeV

Antitau 1.78 GeV

Tau neutrino < 2 eV ****

Tau antineutrino < 2 eV ****

Top quark 171 GeV

Top antiquark 171 GeV

Bottom quark ~ 4.2 GeV

Bottom antiquark ~ 4.2 GeV

Notes:

• * These are not ordinary abelian charges, which can be added together, but are labels of group representations of Lie groups.• ** Mass is really a coupling between a left-handed fermion and a right-handed fermion. For example, the mass of an electron is really a

coupling between a left-handed electron and a right-handed electron, which is the antiparticle of a left-handed positron. Also neutrinos showlarge mixings in their mass coupling, so it's not accurate to talk about neutrino masses in the flavor basis or to suggest a left-handed electronantineutrino.

• *** The masses of baryons and hadrons and various cross-sections are the experimentally measured quantities. Since quarks can't be isolatedbecause of QCD confinement, the quantity here is supposed to be the mass of the quark at the renormalization scale of the QCD scale.

• **** The Standard Model assumes that neutrinos are massless. However, several contemporary experiments prove that neutrinos oscillatebetween their flavour states, which could not happen if all were massless.[20] It is straightforward to extend the model to fit these data but thereare many possibilities, so the mass eigenstates are still open. See Neutrino#Mass.

Log plot of masses in the Standard Model.

Tests and predictions

The Standard Model (SM) predictedthe existence of the W and Z bosons,gluon, and the top and charm quarksbefore these particles were observed.Their predicted properties wereexperimentally confirmed with goodprecision. To give an idea of thesuccess of the SM, the following table compares the measured masses of the W and Z bosons with the massespredicted by the SM:

Standard Model 67

Quantity Measured (GeV) SM prediction (GeV)

Mass of W boson 80.398 ± 0.025 80.390 ± 0.018

Mass of Z boson 91.1876 ± 0.0021 91.1874 ± 0.0021

The SM also makes several predictions about the decay of Z bosons, which have been experimentally confirmed bythe Large Electron-Positron Collider at CERN.

Challenges to the standard modelThere is some experimental evidence consistent with neutrinos having mass, which the Standard Model does notallow.[21] To accommodate such findings, the Standard Model can be modified by adding a non-renormalizableinteraction of lepton fields with the square of the Higgs field. This is natural in certain grand unified theories, and ifnew physics appears at about 1016 GeV, the neutrino masses are of the right order of magnitude.Currently, there is one elementary particle predicted by the Standard Model that has yet to be observed: the Higgsboson. A major reason for building the Large Hadron Collider is that the high energies of which it is capable areexpected to make the Higgs observable. However, as of January 2011, there is only indirect empirical evidence forthe existence of the Higgs boson, so that its discovery cannot be claimed. Moreover, there are serious theoreticalreasons for supposing that elementary scalar Higgs particles cannot exist (see Quantum triviality).A fair amount of theoretical and experimental research has attempted to extend the Standard Model into a UnifiedField Theory or a Theory of everything, a complete theory explaining all physical phenomena including constants.Inadequacies of the Standard Model that motivate such research include:• It does not attempt to explain gravitation, and unlike for the strong and electroweak interactions of the Standard

Model, there is no known way of describing general relativity, the canonical theory of gravitation, consistently interms of quantum field theory. The reason for this is among other things that quantum field theories of gravitygenerally break down before reaching the Planck scale. As a consequence, we have no reliable theory for the veryearly universe;

• It seems rather ad-hoc and inelegant, requiring 19 numerical constants whose values are unrelated and arbitrary.Although the Standard Model, as it now stands, can explain why neutrinos have masses, the specifics of neutrinomass are still unclear. It is believed that explaining neutrino mass will require an additional 7 or 8 constants,which are also arbitrary parameters;

• The Higgs mechanism gives rise to the hierarchy problem if any new physics (such as quantum gravity) is presentat high energy scales. In order for the weak scale to be much smaller than the Planck scale, severe fine tuning ofStandard Model parameters is required;

• It should be modified so as to be consistent with the emerging "standard model of cosmology." In particular, theStandard Model cannot explain the observed amount of cold dark matter (CDM) and gives contributions to darkenergy which are far too large. It is also difficult to accommodate the observed predominance of matter overantimatter (matter/antimatter asymmetry). The isotropy and homogeneity of the visible universe over largedistances seems to require a mechanism like cosmic inflation, which would also constitute an extension of theStandard Model.

Currently no proposed Theory of everything has been conclusively verified.

Standard Model 68

Notes and references

Notes

[1] S.L. Glashow (1961). "Partial-symmetries of weak interactions". Nuclear Physics 22: 579–588. doi:10.1016/0029-5582(61)90469-2.[2] S. Weinberg (1967). "A Model of Leptons". Physical Review Letters 19: 1264–1266. doi:10.1103/PhysRevLett.19.1264.[3] A. Salam (1968). N. Svartholm. ed. Elementary Particle Physics: Relativistic Groups and Analyticity. Eighth Nobel Symposium. Stockholm:

Almquvist and Wiksell. pp. 367.[4] F. Englert, R. Brout (1964). "Broken Symmetry and the Mass of Gauge Vector Mesons". Physical Review Letters 13: 321–323.

doi:10.1103/PhysRevLett.13.321.[5] P.W. Higgs (1964). "Broken Symmetries and the Masses of Gauge Bosons". Physical Review Letters 13: 508–509.

doi:10.1103/PhysRevLett.13.508.[6] G.S. Guralnik, C.R. Hagen, T.W.B. Kibble (1964). "Global Conservation Laws and Massless Particles". Physical Review Letters 13:

585–587. doi:10.1103/PhysRevLett.13.585.[7] F.J. Hasert et al. (1973). "Search for elastic muon-neutrino electron scattering". Physics Letters B 46: 121.

doi:10.1016/0370-2693(73)90494-2.[8] F.J. Hasert et al. (1973). "Observation of neutrino-like interactions without muon or electron in the gargamelle neutrino experiment". Physics

Letters B 46: 138. doi:10.1016/0370-2693(73)90499-1.[9] F.J. Hasert et al. (1974). "Observation of neutrino-like interactions without muon or electron in the Gargamelle neutrino experiment". Nuclear

Physics B 73: 1. doi:10.1016/0550-3213(74)90038-8.[10] D. Haidt (4 October 2004). "The discovery of the weak neutral currents" (http:/ / cerncourier. com/ cws/ article/ cern/ 29168). CERN

Courier. . Retrieved 2008-05-08.[11] "Details can be worked out if the situation is simple enough for us to make an approximation, which is almost never, but often we can

understand more or less what is happening." from The Feynman Lectures on Physics, Vol 1. pp. 2–7[12] Technically, there are nine such color–anticolor combinations. However there is one color symmetric combination that can be constructed

out of a linear superposition of the nine combinations, reducing the count to eight.[13] F. Englert, R. Brout (1964). "Broken Symmetry and the Mass of Gauge Vector Mesons". Physical Review Letters 13: 321–323.

doi:10.1103/PhysRevLett.13.321.[14] P.W. Higgs (1964). "Broken Symmetries and the Masses of Gauge Bosons". Physical Review Letters 13: 508–509.

doi:10.1103/PhysRevLett.13.508.[15] G.S. Guralnik, C.R. Hagen, T.W.B. Kibble (1964). "Global Conservation Laws and Massless Particles". Physical Review Letters 13:

585–587. doi:10.1103/PhysRevLett.13.585.[16] G.S. Guralnik (2009). "The History of the Guralnik, Hagen and Kibble development of the Theory of Spontaneous Symmetry Breaking and

Gauge Particles". International Journal of Modern Physics A 24: 2601–2627. doi:10.1142/S0217751X09045431. arXiv:0907.3466.[17] A. Cho (23 January 2008). "Higgs Hiding in Plain Sight?" (http:/ / sciencenow. sciencemag. org/ cgi/ content/ full/ 2008/ 123/ 3).

ScienceNOW. . Retrieved 2008-05-08.[18] The normalization Q = I3 + Y is sometimes used instead.[19] W.-M. Yao et al. (Particle Data Group) (2006). "Review of Particle Physics: Quarks" (http:/ / pdg. lbl. gov/ 2006/ tables/ qxxx. pdf). Journal

of Physics G 33: 1. doi:10.1088/0954-3899/33/1/001. .[20] W.-M. Yao et al. (Particle Data Group) (2006). "Review of Particle Physics: Neutrino mass, mixing, and flavor change" (http:/ / pdg. lbl.

gov/ 2007/ reviews/ numixrpp. pdf). Journal of Physics G 33: 1. .[21] http:/ / press. web. cern. ch/ press/ PressReleases/ Releases2010/ PR08. 10E. html

References

Further reading• R. Oerter (2006). The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern

Physics. Plume.• B.A. Schumm (2004). Deep Down Things: The Breathtaking Beauty of Particle Physics. Johns Hopkins

University Press. ISBN 0-8018-7971-X.• V. Stenger (2000). Timeless Reality. Prometheus Books. See chapters 9–12 in particular.Introductory textbooks• I. Aitchison, A. Hey (2003). Gauge Theories in Particle Physics: A Practical Introduction.. Institute of Physics.

ISBN 9780585445502.• W. Greiner, B. Müller (2000). Gauge Theory of Weak Interactions. Springer. ISBN 3-540-67672-4.

Standard Model 69

• G.D. Coughlan, J.E. Dodd, B.M. Gripaios (2006). The Ideas of Particle Physics: An Introduction for Scientists.Cambridge University Press.

• D.J. Griffiths (1987). Introduction to Elementary Particles. John Wiley & Sons. ISBN 0-471-60386-4.• G.L. Kane (1987). Modern Elementary Particle Physics. Perseus Books. ISBN 0-201-11749-5.Advanced textbooks• T.P. Cheng, L.F. Li (2006). Gauge theory of elementary particle physics. Oxford University Press.

ISBN 0-19-851961-3. Highlights the gauge theory aspects of the Standard Model.• J.F. Donoghue, E. Golowich, B.R. Holstein (1994). Dynamics of the Standard Model. Cambridge University

Press. ISBN 978-0521476522. Highlights dynamical and phenomenological aspects of the Standard Model.• L. O'Raifeartaigh (1988). Group structure of gauge theories. Cambridge University Press. ISBN 0-521-34785-8.

Highlights group-theoretical aspects of the Standard Model.Journal articles• E.S. Abers, B.W. Lee (1973). "Gauge theories". Physics Reports 9: 1–141. doi:10.1016/0370-1573(73)90027-6.• Y. Hayato et al. (1999). "Search for Proton Decay through p → νK+ in a Large Water Cherenkov Detector".

Physical Review Letters 83: 1529. doi:10.1103/PhysRevLett.83.1529.• S.F. Novaes (2000). "Standard Model: An Introduction". arΧiv:hep-ph/0001283 [hep-ph].• D.P. Roy (1999). "Basic Constituents of Matter and their Interactions — A Progress Report.".

arΧiv:hep-ph/9912523 [hep-ph].• F. Wilczek (2004). "The Universe Is A Strange Place". arΧiv:astro-ph/0401347 [astro-ph].

External links• " Standard Model - explanation for beginners (http:/ / cms. web. cern. ch/ cms/ Physics/ StandardPackage/ index.

html)" LHC• " Standard Model may be found incomplete, (http:/ / www. newscientist. com/ news/ news. jsp?id=ns9999404)"

New Scientist.• " Observation of the Top Quark (http:/ / www-cdf. fnal. gov/ top_status/ top. html)" at Fermilab.• " The Standard Model Lagrangian. (http:/ / cosmicvariance. com/ 2006/ 11/ 23/ thanksgiving)" After electroweak

symmetry breaking, with no explicit Higgs boson.• " Standard Model Lagrangian (http:/ / nuclear. ucdavis. edu/ ~tgutierr/ files/ stmL1. html)" with explicit Higgs

terms. PDF, PostScript, and LaTeX versions.• " The particle adventure. (http:/ / particleadventure. org/ )" Web tutorial.• Nobes, Matthew (2002) "Introduction to the Standard Model of Particle Physics" on Kuro5hin: Part 1, (http:/ /

www. kuro5hin. org/ story/ 2002/ 5/ 1/ 3712/ 31700) Part 2, (http:/ / www. kuro5hin. org/ story/ 2002/ 5/ 14/19363/ 8142) Part 3a, (http:/ / www. kuro5hin. org/ story/ 2002/ 7/ 15/ 173318/ 784) Part 3b. (http:/ / www.kuro5hin. org/ story/ 2002/ 8/ 21/ 195035/ 576)

Particle physics 70

Particle physics

Collision of 2 beams of gold atoms recorded by RHIC

Particle physics is a branch of physics that studies theelementary subatomic constituents of matter andradiation, and their interactions. The field is also calledhigh energy physics, because many elementaryparticles do not occur under ambient conditions onEarth. They can only be created artificially during highenergy collisions with other particles in particleaccelerators.

Particle physics has evolved out of its parent field ofnuclear physics and is typically still taught in closeassociation with it. Scientific research in this area hasproduced a long list of particles.

Subatomic particles

An image showing 6 quarks, 6 leptons and the interacting particles, according tothe Standard Model

Modern particle physics research is focusedon subatomic particles, including atomicconstituents such as electrons, protons, andneutrons (protons and neutrons are actuallycomposite particles, made up of quarks),particles produced by radioactive andscattering processes, such as photons,neutrinos, and muons, as well as a widerange of exotic particles.

Strictly speaking, the term particle is amisnomer from classical physics becausethe dynamics of particle physics aregoverned by quantum mechanics. As such,they exhibit wave-particle duality,displaying particle-like behavior undercertain experimental conditions andwave-like behavior in others. In moretechnical terms, they are described by statevectors in a Hilbert space, which is alsotreated in quantum field theory. Followingthe convention of particle physicists,elementary particles refer to objects such aselectrons and photons, it is well known that these types of particles display wave-like properties as well.

All particles and their interactions observed to date can almost be described entirely by a quantum field theory called the Standard Model. The Standard Model has 17 species of elementary particles: 12 fermions or 24 if distinguishing antiparticles, 4 vector bosons (5 with antiparticles), and 1 scalar boson. These elementary particles can combine to

Particle physics 71

form composite particles, accounting for the hundreds of other species of particles discovered since the 1960s. TheStandard Model has been found to agree with almost all the experimental tests conducted to date. However, mostparticle physicists believe that it is an incomplete description of nature, and that a more fundamental theory awaitsdiscovery. In recent years, measurements of neutrino mass have provided the first experimental deviations from theStandard Model.Particle physics has impacted the philosophy of science greatly. Some particle physicists adhere to reductionism, apoint of view that has been criticized and defended by philosophers and scientists.[1] [2] [3] [4]

HistoryThe idea that all matter is composed of elementary particles dates to at least the 6th century BC. The philosophicaldoctrine of atomism and the nature of elementary particles were studied by ancient Greek philosophers such asLeucippus, Democritus and Epicurus; ancient Indian philosophers such as Kanada, Dignāga and Dharmakirti;medieval scientists such as Alhazen, Avicenna and Algazel; and early modern European physicists such as PierreGassendi, Robert Boyle and Isaac Newton. The particle theory of light was also proposed by Alhazen, Avicenna,Gassendi and Newton. These early ideas were founded in abstract, philosophical reasoning rather thanexperimentation and empirical observation.In the 19th century, John Dalton, through his work on stoichiometry, concluded that each element of nature wascomposed of a single, unique type of particle. Dalton and his contemporaries believed these were the fundamentalparticles of nature and thus named them atoms, after the Greek word atomos, meaning "indivisible". However, nearthe end of the century, physicists discovered that atoms were not, in fact, the fundamental particles of nature, butconglomerates of even smaller particles. The early 20th century explorations of nuclear physics and quantum physicsculminated in proofs of nuclear fission in 1939 by Lise Meitner (based on experiments by Otto Hahn), and nuclearfusion by Hans Bethe in the same year. These discoveries gave rise to an active industry of generating one atom fromanother, even rendering possible (although not profitable) the transmutation of lead into gold. They also led to thedevelopment of nuclear weapons. Throughout the 1950s and 1960s, a bewildering variety of particles were found inscattering experiments. This was referred to as the "particle zoo". This term was deprecated after the formulation ofthe Standard Model during the 1970s in which the large number of particles was explained as combinations of a(relatively) small number of fundamental particles.

The Standard ModelThe current state of the classification of elementary particles is the Standard Model. It describes the strong, weak,and electromagnetic fundamental forces, using mediating gauge bosons. The species of gauge bosons are the gluons,W− and W+ and Z bosons, and the photons. The model also contains 24 fundamental particles, which are theconstituents of matter. Finally, it predicts the existence of a type of boson known as the Higgs boson, which is yet tobe discovered.

Experimental laboratoriesIn particle physics, the major international laboratories are:• Brookhaven National Laboratory (Long Island, United States). Its main facility is the Relativistic Heavy Ion

Collider (RHIC) which collides heavy ions such as gold ions and polarized protons. It is the world's first heavyion collider, and the world's only polarized proton collider.

• Budker Institute of Nuclear Physics (Novosibirsk, Russia)• CERN, (Franco-Swiss border, near Geneva). Its main project is now the Large Hadron Collider (LHC), which had

its first beam circulation on 10 September 2008, and is now the world's most energetic collider of protons. It will also be the most energetic collider of heavy ions when it begins colliding lead ions in 2010. Earlier facilities

Particle physics 72

include the Large Electron–Positron Collider (LEP), which was stopped in 2001 and then dismantled to give wayfor LHC; and the Super Proton Synchrotron, which is being reused as a pre-accelerator for LHC.

• DESY (Hamburg, Germany). Its main facility is the Hadron Elektron Ring Anlage (HERA), which collideselectrons and positrons with protons.

• Fermilab, (Batavia, United States). Its main facility is the Tevatron, which collides protons and antiprotons andwas the highest energy particle collider in the world until the Large Hadron Collider surpassed it on 29 November2009.

• KEK, (Tsukuba, Japan). It is the home of a number of experiments such as K2K, a neutrino oscillation experimentand Belle, an experiment measuring the CP violation of B mesons.

• SLAC National Accelerator Laboratory (Menlo Park, United States). Its main facility is PEP-II, which collideselectrons and positrons.

Many other particle accelerators exist.The techniques required to do modern experimental particle physics are quite varied and complex, constituting asub-specialty nearly completely distinct from the theoretical side of the field.

TheoryTheoretical particle physics attempts to develop the models, theoretical framework, and mathematical tools tounderstand current experiments and make predictions for future experiments. See also theoretical physics. There areseveral major interrelated efforts in theoretical particle physics today. One important branch attempts to betterunderstand the Standard Model and its tests. By extracting the parameters of the Standard Model from experimentswith less uncertainty, this work probes the limits of the Standard Model and therefore expands our understanding ofnature's building blocks. These efforts are made challenging by the difficulty of calculating quantities in quantumchromodynamics. Some theorists working in this area refer to themselves as phenomenologists and may use thetools of quantum field theory and effective field theory. Others make use of lattice field theory and call themselveslattice theorists.Another major effort is in model building where model builders develop ideas for what physics may lie beyond theStandard Model (at higher energies or smaller distances). This work is often motivated by the hierarchy problem andis constrained by existing experimental data. It may involve work on supersymmetry, alternatives to the Higgsmechanism, extra spatial dimensions (such as the Randall-Sundrum models), Preon theory, combinations of these, orother ideas.A third major effort in theoretical particle physics is string theory. String theorists attempt to construct a unifieddescription of quantum mechanics and general relativity by building a theory based on small strings, and branesrather than particles. If the theory is successful, it may be considered a "Theory of Everything".There are also other areas of work in theoretical particle physics ranging from particle cosmology to loop quantumgravity.This division of efforts in particle physics is reflected in the names of categories on the preprint archive [5]: hep-th(theory), hep-ph (phenomenology), hep-ex (experiments), hep-lat (lattice gauge theory).

The futureParticle physicists internationally agree on the most important goals of particle physics research in the near andintermediate future. The overarching goal, which is pursued in several distinct ways, is to find and understand whatphysics may lie beyond the standard model. There are several powerful experimental reasons to expect new physics,including dark matter and neutrino mass. There are also theoretical hints that this new physics should be found ataccessible energy scales. Most importantly, though, there may be unexpected and unpredicted surprises which willgive us the most opportunity to learn about nature.

Particle physics 73

Much of the efforts to find this new physics are focused on new collider experiments. A (relatively) near term goal isthe completion of the Large Hadron Collider (LHC) in 2008 which will continue the search for the Higgs boson,supersymmetric particles, and other new physics. An intermediate goal is the construction of the International LinearCollider (ILC) which will complement the LHC by allowing more precise measurements of the properties of newlyfound particles. A decision for the technology of the ILC has been taken in August 2004, but the site has still to beagreed upon.Additionally, there are important non-collider experiments which also attempt to find and understand physics beyondthe Standard Model. One important non-collider effort is the determination of the neutrino masses since these massesmay arise from neutrinos mixing with very heavy particles. In addition, cosmological observations provide manyuseful constraints on the dark matter, although it may be impossible to determine the exact nature of the dark matterwithout the colliders. Finally, lower bounds on the very long lifetime of the proton put constraints on GrandUnification Theories at energy scales much higher than collider experiments will be able to probe any time soon.

References[1] "Review of particle physics" (http:/ / pdg. lbl. gov/ ). .[2] "Particle Physics News and Resources" (http:/ / www. interactions. org/ ). .[3] "CERN Courier - International Journal of High-Energy Physics" (http:/ / cerncourier. com). .[4] "Particle physics in 60 seconds" (http:/ / www. symmetrymagazine. org/ cms/ ?pid=1000345). .[5] http:/ / www. arxiv. org

Further reading

General readers• Frank Close (2004) Particle Physics: A Very Short Introduction. Oxford University Press. ISBN 0-19-280434-0.• --------, Michael Marten, and Christine Sutton (2002) The Particle Odyssey: A Journey to the Heart of the Matter.

Oxford Univ. Press. ISBN 0-19-850486-1.• Ford, Kenneth W. (2005) The Quantum World. Harvard Univ. Press.• Oerter, Robert (2006) The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern

Physics. Plume.• Schumm, Bruce A. (2004) Deep Down Things: The Breathtaking Beauty of Particle Physics. John Hopkins Univ.

Press. ISBN 0-8018-7971-X.

Gentle texts• Frank Close (2006) The New Cosmic Onion. Taylor & Francis. ISBN 1-58488-798-2.• Coughlan, G. D., J. E. Dodd, and B. M. Gripaios (2006) The Ideas of Particle Physics: An Introduction for

Scientists, 3rd ed. Cambridge Univ. Press. An undergraduate text for those not majoring in physics.

HarderA survey article:• Robinson, Matthew B., Karen R. Bland, Gerald Cleaver, and J. R. Dittmann (2008) "A Simple Introduction to

Particle Physics" - Part 1, 135pp. (http:/ / arxiv. org/ abs/ 0810. 3328v1) and Part 2, nnnpp. (http:/ / arxiv. org/abs/ 0908. 1395v1) Baylor University Dept. of Physics.

Texts:• Griffiths, David J. (1987). Introduction to Elementary Particles. Wiley, John & Sons, Inc. ISBN 0-471-60386-4.• Kane, Gordon L. (1987). Modern Elementary Particle Physics. Perseus Books. ISBN 0-201-11749-5.

Particle physics 74

• Perkins, Donald H. (1999). Introduction to High Energy Physics. Cambridge University Press.ISBN 0-521-62196-8.

• Povh, Bogdan (1995). Particles and Nuclei: An Introduction to the Physical Concepts. Springer-Verlag.ISBN 0-387-59439-6.

External links• The Particle Adventure (http:/ / particleadventure. org/ ) - educational project sponsored by the Particle Data

Group of the Lawrence Berkeley National Laboratory (LBNL)• symmetry magazine (http:/ / www. symmetrymagazine. org)• Nobes, Matthew (2002) "Introduction to the Standard Model of Particle Physics" on Kuro5hin: Part 1, (http:/ /

www. kuro5hin. org/ story/ 2002/ 5/ 1/ 3712/ 31700) Part 2, (http:/ / www. kuro5hin. org/ story/ 2002/ 5/ 14/19363/ 8142) Part 3a, (http:/ / www. kuro5hin. org/ story/ 2002/ 7/ 15/ 173318/ 784) Part 3b. (http:/ / www.kuro5hin. org/ story/ 2002/ 8/ 21/ 195035/ 576)

• CERN (http:/ / public. web. cern. ch/ public/ ) - European Organization for Nuclear Research• Fermilab (http:/ / www. fnal. gov/ )

SuperpartnerIn particle physics, a superpartner (also sparticle) is a hypothetical elementary particle. Supersymmetry is one ofthe synergistic bleeding-edge theories in current high-energy physics which predicts the existence of these "shadow"particles.The word superpartner is a portmanteau of the words supersymmetry and partner (sparticle is a portmanteau ofsupersymmetry and particle).

Theoretical predictionsAccording to the supersymmetry theory, each fermion should have a partner boson, the fermion's superpartner andeach boson should have a partner fermion. When the more familiar leptons, photons, and quarks were produced inthe Big Bang, each one was accompanied by a matching sparticle: sleptons, photinos and squarks. This state ofaffairs occurred at a time when the universe was undergoing a rapid phase change, and theorists believe this state ofaffairs lasted only some ten trillionth of a ten trillionth of a nanosecond (10−35 seconds) before the particles we seenow "condensed" out and froze into space-time. Sparticles have not existed naturally since that time.Exact unbroken supersymmetry would predict that a particle and its superpartners would have the same mass. Nosuperpartners of the Standard Model particles have yet been found. This may indicate that supersymmetry isincorrect, or it may also be the result of the fact that supersymmetry is not an exact, unbroken symmetry of nature. Ifa superpartner is found, its mass would determine the scale at which supersymmetry is broken.For particles that are real scalars (such as an axion), there is a fermion superpartner as well as a second, real scalarfield. For axions, these particles are often referred to as axinos and saxions.In extended supersymmetry there may be more than one superparticle for a given particle. For instance, with twocopies of supersymmetry in four dimensions, a photon would have two fermion superpartners and a scalarsuperpartner.In zero dimensions (often known as matrix mechanics), it is possible to have supersymmetry, but no superpartners.However, this is the only situation where supersymmetry does not imply the existence of superpartners.

Superpartner 75

Recreating superpartnersIf the supersymmetry theory is correct, it should be possible to recreate these particles in high-energy particleaccelerators. Doing so will not be an easy task; these particles may have masses up to a thousand times greater thantheir corresponding "real" particles.Until recently, colliders did not have the power to create these supermassive particles, but the newly built LargeHadron Collider at CERN in Switzerland and France will be able to achieve collisions in the 14 TeV(tera-electron-volt) range, which is more than adequate to determine if these superpartner particles exist.

External links• Argonne National Laboratory [1]

• Large Hadron Collider [2]

• CERN homepage [3]

References[1] http:/ / www. anl. gov/ OPA/ Frontiers2000/ b5excell. html[2] https:/ / edms. cern. ch/ cedar/ plsql/ cedarw. site_home[3] http:/ / public. web. cern. ch/ public/

SupersymmetryIn particle physics, supersymmetry (often abbreviated SUSY) is a symmetry that relates elementary particles of onespin to other particles that differ by half a unit of spin and are known as superpartners. In a theory with unbrokensupersymmetry, for every type of boson there exists a corresponding type of fermion with the same mass and internalquantum numbers, and vice-versa.So far, there is only indirect evidence for the existence of supersymmetry.[1] Since the superpartners of the StandardModel particles have not been observed, supersymmetry, if it exists, must be a broken symmetry, allowing thesuperparticles to be heavier than the corresponding Standard Model particles.If supersymmetry exists close to the TeV energy scale, it allows for a solution of the hierarchy problem of theStandard Model, i.e., the fact that the Higgs boson mass is subject to quantum corrections which — barringextremely fine-tuned cancellations among independent contributions — would make it so large as to undermine theinternal consistency of the theory. In supersymmetric theories, on the other hand, the contributions to the quantumcorrections coming from Standard Model particles are naturally canceled by the contributions of the correspondingsuperpartners. Other attractive features of TeV-scale supersymmetry are the fact that it allows for the high-energyunification of the weak interactions, the strong interactions and electromagnetism, and the fact that it provides acandidate for Dark Matter and a natural mechanism for electroweak symmetry breaking.Another advantage of supersymmetry is that supersymmetric quantum field theory can sometimes be solved.Supersymmetry is also a feature of most versions of string theory, though it can exist in nature even if string theoryis incorrect.The Minimal Supersymmetric Standard Model is one of the best studied candidates for physics beyond the StandardModel. Theories of gravity that are also invariant under supersymmetry are known as supergravity theories.

Supersymmetry 76

HistoryA supersymmetry relating mesons and baryons was first proposed, in the context of hadronic physics, by HironariMiyazawa in 1966, but his work was ignored at the time.[2] [3] [4] [5] In the early 1970s, J. L. Gervais and B. Sakita(in 1971), Yu. A. Golfand and E.P. Likhtman (also in 1971), D.V. Volkov and V.P. Akulov (in 1972) and J. Wessand B. Zumino (in 1974) independently rediscovered supersymmetry, a radically new type of symmetry of spacetimeand fundamental fields, which establishes a relationship between elementary particles of different quantum nature,bosons and fermions, and unifies spacetime and internal symmetries of the microscopic world. Supersymmetry firstarose in the context of an early version of string theory by Pierre Ramond, John H. Schwarz and Andre Neveu, butthe mathematical structure of supersymmetry has subsequently been applied successfully to other areas of physics;firstly by Wess, Zumino, and Abdus Salam and their fellow researchers to particle physics, and later to a variety offields, ranging from quantum mechanics to statistical physics. It remains a vital part of many proposed theories ofphysics.The first realistic supersymmetric version of the Standard Model was proposed in 1981 by Howard Georgi and SavasDimopoulos and is called the Minimal Supersymmetric Standard Model or MSSM for short. It was proposed to solvethe hierarchy problem and predicts superpartners with masses between 100 GeV and 1 TeV. As of 2009 there is noirrefutable experimental evidence that supersymmetry is a symmetry of nature. In 2010 the Large Hadron Collider atCERN is scheduled to produce the world's highest energy collisions and offers the best chance at discoveringsuperparticles for the foreseeable future. Recently prediction markets like intrade offered scientific contracts thatgive estimates for that probability.

Applications

Extension of possible symmetry groupsOne reason that physicists explored supersymmetry is because it offers an extension to the more familiar symmetriesof quantum field theory. These symmetries are grouped into the Poincaré group and internal symmetries and theColeman–Mandula theorem showed that under certain assumptions, the symmetries of the S-matrix must be a directproduct of the Poincaré group with a compact internal symmetry group or if there is no mass gap, the conformalgroup with a compact internal symmetry group. In 1971 Golfand and Likhtman were the first to show that thePoincaré algebra can be extended through introduction of four anticommuting spinor generators (in fourdimensions), which later became known as supercharges. In 1975 the Haag-Lopuszanski-Sohnius theorem analyzedall possible superalgebras in the general form, including those with an extended number of the supergenerators andcentral charges. This extended super-Poincaré algebra paved the way for obtaining a very large and important classof supersymmetric field theories.

The supersymmetry algebra

Traditional symmetries in physics are generated by objects that transform under the tensor representations of thePoincaré group and internal symmetries. Supersymmetries, on the other hand, are generated by objects that transformunder the spinor representations. According to the spin-statistics theorem, bosonic fields commute while fermionicfields anticommute. Combining the two kinds of fields into a single algebra requires the introduction of a Z2-gradingunder which the bosons are the even elements and the fermions are the odd elements. Such an algebra is called a Liesuperalgebra.The simplest supersymmetric extension of the Poincaré algebra is the Super-Poincaré algebra. Expressed in terms oftwo Weyl spinors, has the following anti-commutation relation:

Supersymmetry 77

and all other anti-commutation relations between the Qs and commutation relations between the Qs and Ps vanish. Inthe above expression are the generators of translation and are the Pauli matrices.There are representations of a Lie superalgebra that are analogous to representations of a Lie algebra. Each Liealgebra has an associated Lie group and a Lie superalgebra can sometimes be extended into representations of a Liesupergroup.

The Supersymmetric Standard ModelIncorporating supersymmetry into the Standard Model requires doubling the number of particles since there is noway that any of the particles in the Standard Model can be superpartners of each other. With the addition of newparticles, there are many possible new interactions. The simplest possible supersymmetric model consistent with theStandard Model is the Minimal Supersymmetric Standard Model (MSSM) which can include the necessaryadditional new particles that are able to be superpartners of those in the Standard Model.

Cancellation of the Higgs boson quadratic mass renormalization between fermionictop quark loop and scalar stop squark tadpole Feynman diagrams in a

supersymmetric extension of the Standard Model

One of the main motivations for SUSYcomes from the quadratically divergentcontributions to the Higgs mass squared.The quantum mechanical interactions of theHiggs boson causes a large renormalizationof the Higgs mass and unless there is anaccidental cancellation, the natural size ofthe Higgs mass is the highest scale possible.This problem is known as the hierarchyproblem. Supersymmetry reduces the size ofthe quantum corrections by havingautomatic cancellations between fermionicand bosonic Higgs interactions. Ifsupersymmetry is restored at the weak scale,then the Higgs mass is related tosupersymmetry breaking which can beinduced from small non-perturbative effectsexplaining the vastly different scales in theweak interactions and gravitational interactions.

In many supersymmetric Standard Models there is a heavy stable particle (such as neutralino) which could serve as aWeakly interacting massive particle (WIMP) dark matter candidate. The existence of a supersymmetric dark mattercandidate is closely tied to R-parity.

The standard paradigm for incorporating supersymmetry into a realistic theory is to have the underlying dynamics ofthe theory be supersymmetric, but the ground state of the theory does not respect the symmetry and supersymmetryis broken spontaneously. The supersymmetry break can not be done permanently by the particles of the MSSM asthey currently appear. This means that there is a new sector of the theory that is responsible for the breaking. Theonly constraint on this new sector is that it must break supersymmetry permanently and must give superparticles TeVscale masses. There are many models that can do this and most of their details do not currently matter. In order toparameterize the relevant features of supersymmetry breaking, arbitrary soft SUSY breaking terms are added to thetheory which temporarily break SUSY explicitly but could never arise from a complete theory of supersymmetrybreaking.

Supersymmetry 78

Gauge Coupling Unification

One piece of evidence for supersymmetry existing is gauge coupling unification. The renormalization groupevolution of the three gauge coupling constants of the Standard Model is somewhat sensitive to the present particlecontent of the theory. These coupling constants do not quite meet together at a common energy scale if we run therenormalization group using the Standard Model.[1] With the addition of minimal SUSY joint convergence of thecoupling constants is projected at approximately 1016 GeV.[1]

Supersymmetric quantum mechanicsSupersymmetric quantum mechanics adds the SUSY superalgebra to quantum mechanics as opposed to quantumfield theory. Supersymmetric quantum mechanics often comes up when studying the dynamics of supersymmetricsolitons and due to the simplified nature of having fields only functions of time (rather than space-time), a great dealof progress has been made in this subject and is now studied in its own right.SUSY quantum mechanics involves pairs of Hamiltonians which share a particular mathematical relationship, whichare called partner Hamiltonians. (The potential energy terms which occur in the Hamiltonians are then calledpartner potentials.) An introductory theorem shows that for every eigenstate of one Hamiltonian, its partnerHamiltonian has a corresponding eigenstate with the same energy. This fact can be exploited to deduce manyproperties of the eigenstate spectrum. It is analogous to the original description of SUSY, which referred to bosonsand fermions. We can imagine a "bosonic Hamiltonian", whose eigenstates are the various bosons of our theory. TheSUSY partner of this Hamiltonian would be "fermionic", and its eigenstates would be the theory's fermions. Eachboson would have a fermionic partner of equal energy.SUSY concepts have provided useful extensions to the WKB approximation. In addition, SUSY has been applied tonon-quantum statistical mechanics through the Fokker-Planck equation.

MathematicsSUSY is also sometimes studied mathematically for its intrinsic properties. This is because it describes complexfields satisfying a property known as holomorphy, which allows holomorphic quantities to be exactly computed.This makes supersymmetric models useful toy models of more realistic theories. A prime example of this has beenthe demonstration of S-duality in four-dimensional gauge theories that interchanges particles and monopoles.

General supersymmetrySupersymmetry appears in many different contexts in theoretical physics that are closely related. It is possible tohave multiple supersymmetries and also have supersymmetric extra dimensions.

Extended supersymmetryIt is possible to have more than one kind of supersymmetry transformation. Theories with more than onesupersymmetry transformation are known as extended supersymmetric theories. The more supersymmetry a theoryhas, the more constrained the field content and interactions are. Typically the number of copies of a supersymmetryis a power of 2, i.e. 1, 2, 4, 8. In four dimensions, a spinor has four degrees of freedom and thus the minimal numberof supersymmetry generators is four in four dimensions and having eight copies of supersymmetry means that thereare 32 supersymmetry generators.The maximal number of supersymmetry generators possible is 32. Theories with more than 32 supersymmetrygenerators automatically have massless fields with spin greater than 2. It is not known how to make massless fieldswith spin greater than two interact, so the maximal number of supersymmetry generators considered is 32. Thiscorresponds to an N = 8 supersymmetry theory. Theories with 32 supersymmetries automatically have a graviton.

Supersymmetry 79

In four dimensions there are the following theories, with the corresponding multiplets [6] (CPT adds a copy,whenever they are not invariant under such symmetry)• N = 1Chiral multiplet: (0,1⁄2) Vector multiplet: (1⁄2,1) Gravitino multiplet: (1,3⁄2) Graviton multiplet: (3⁄2,2)• N = 2hypermultiplet: (-1⁄2,02,1⁄2) vector multiplet: (0,1⁄2

2,1) supergravity multiplet: (1,3⁄22,2)

• N = 4Vector multiplet: (-1,-1⁄2

4,06,1⁄24,1) Supergravity multiplet: (0,1⁄2

4,16,3⁄24,2)

• N = 8Supergravity multiplet: (-2,-3⁄2

8,-128,-1⁄256,070,1⁄2

56,128,3⁄28,2)

Supersymmetry in alternate numbers of dimensionsIt is possible to have supersymmetry in dimensions other than four. Because the properties of spinors changedrastically between different dimensions, each dimension has its characteristic. In d dimensions, the size of spinors isroughly 2d/2 or 2(d − 1)/2. Since the maximum number of supersymmetries is 32, the greatest number of dimensions inwhich a supersymmetric theory can exist is eleven.

Supersymmetry as a quantum groupSupersymmetry can be reinterpreted in the language of noncommutative geometry and quantum groups. Inparticular, it involves a mild form of noncommutativity, namely supercommutativity. See the main article for moredetails.

Supersymmetry in quantum gravitySupersymmetry is part of a larger enterprise of theoretical physics to unify everything we know about the physicalworld into a single fundamental framework of physical laws, known as the quest for a Theory of Everything (TOE).A significant part of this larger enterprise is the quest for a theory of quantum gravity, which would unify theclassical theory of general relativity and the Standard Model, which explains the other three basic forces in physics(electromagnetism, the strong interaction, and the weak interaction), and provides a palette of fundamental particlesupon which all four forces act. Two of the most active approaches to forming a theory of quantum gravity are stringtheory and loop quantum gravity (LQG), although in theory, supersymmetry could be a component of othertheoretical approaches as well.For string theory to be consistent, supersymmetry appears to be required at some level (although it may be a stronglybroken symmetry). In particle theory, supersymmetry is recognized as a way to stabilize the hierarchy between theunification scale and the electroweak scale (or the Higgs boson mass), and can also provide a natural dark mattercandidate. String theory also requires extra spatial dimensions which have to be compactified as in Kaluza-Kleintheory.Loop quantum gravity (LQG), in its current formulation, predicts no additional spatial dimensions, nor anything elseabout particle physics. These theories can be formulated in three spatial dimensions and one dimension of time,although in some LQG theories dimensionality is an emergent property of the theory, rather than a fundamentalassumption of the theory. Also, LQG is a theory of quantum gravity which does not require supersymmetry. LeeSmolin, one of the originators of LQG, has proposed that a loop quantum gravity theory incorporating eithersupersymmetry or extra dimensions, or both, be called "loop quantum gravity II".If experimental evidence confirms supersymmetry in the form of supersymmetric particles such as the neutralino that is often believed to be the lightest superpartner, some people believe this would be a major boost to string theory.

Supersymmetry 80

Since supersymmetry is a required component of string theory, any discovered supersymmetry would be consistentwith string theory. If the Large Hadron Collider and other major particle physics experiments fail to detectsupersymmetric partners or evidence of extra dimensions, many versions of string theory which had predicted certainlow mass superpartners to existing particles may need to be significantly revised. The failure of experiments todiscover either supersymmetric partners or extra spatial dimensions, as of 2009, has encouraged loop quantumgravity researchers.

Current LimitsThe tightest limits will of course come from direct production at colliders. Both the Large Electron–Positron Colliderand Tevatron have set limits for specific models which have not yet been exceeded by the Large Hadron Collider.Searches are only applicable for a finite set of tested points because simulation using the Monte Carlo method mustbe made so that limits for that particular model can be calculated. This complicates matters because differentexperiments have looked at different sets of points. Some extrapolation between points can be made within particularmodels but it is difficult to set general limits even for the Minimal Supersymmetric Standard Model.The first mass limits for squarks and gluinos were made at CERN by the UA1 experiment and the UA2 experimentat the Super Proton Synchrotron. LEP later set very strong limits which are still relevant today [7] . Most recentlythese limits were extended by the D0 experiment [8] [9]

See also• Concise Encyclopedia of Supersymmetry (book)• Minimal Supersymmetric Standard Model• Quantum group• Supercharge• Supergeometry• Supergravity• Supergroup• Superspace

References[1] Gordon L. Kane, The Dawn of Physics Beyond the Standard Model, Scientific American, June 2003, page 60 and The frontiers of physics,

special edition, Vol 15, #3, page 8 "Indirect evidence for supersymmetry comes from the extrapolation of interactions to high energies."[2] H. Miyazawa (1966). "Baryon Number Changing Currents". Prog. Theor. Phys. 36 (6): 1266–1276. doi:10.1143/PTP.36.1266.[3] H. Miyazawa (1968). "Spinor Currents and Symmetries of Baryons and Mesons". Phys. Rev. 170 (5): 1586–1590.

doi:10.1103/PhysRev.170.1586.[4] Michio Kaku, Quantum Field Theory, ISBN 0-19-509158-2, pg 663.[5] Peter Freund, Introduction to Supersymmetry, ISBN 0-521-35675-X, pages 26-27, 138.[6] Polchinski,J. String theory. Vol. 2: Superstring theory and beyond, Appendix B[7] LEPSUSYWG, ALEPH, DELPHI, L3 and OPAL experiments, Charginos, large m0 LEPSUSYWG/01-03.1[8] The D0-Collaboration, Search for associated production of charginos and neutralinos in the trilepton final state using 2.3 $fb^-1$ of data,

arXiv:/0901.0646 [hep-ex][9] The D0 Collaboration, V. Abazov, et al., Search for Squarks and Gluinos in events with jets and missing transverse energy using 2.1 $fb^-1$

of $p\bar{p}$ collision data at $\sqrt{s}$ = 1.96 TeV , arXiv:0712.3805v2 [hep-ex]

Supersymmetry 81

Further reading• Miyazawa Supersymmetry (http:/ / nucl. phys. s. u-tokyo. ac. jp/ kimiko/ fm50/ catto. pdf) by Sultan Catto, 2008• A Supersymmetry Primer (http:/ / arxiv. org/ pdf/ hep-ph/ 9709356) by S. Martin, 1999• Introduction to Supersymmetry (http:/ / arxiv. org/ pdf/ hep-th/ 9612114) By Joseph D. Lykken, 1996• An Introduction to Supersymmetry (http:/ / arxiv. org/ pdf/ hep-ph/ 9611409) By Manuel Drees, 1996• Introduction to Supersymmetry (http:/ / arxiv. org/ pdf/ hep-th/ 0101055) By Adel Bilal, 2001• An Introduction to Global Supersymmetry (http:/ / www. physics. uc. edu/ ~argyres/ 661/ susy2001. pdf) by

Philip Arygres, 2001• Weak Scale Supersymmetry (http:/ / www. cambridge. org/ uk/ catalogue/ catalogue. asp?isbn=0521857864) by

Howard Baer and Xerxes Tata, 2006.• Cooper, F., A. Khare and U. Sukhatme. "Supersymmetry in Quantum Mechanics." Phys. Rep. 251 (1995) 267-85

(arXiv:hep-th/9405029).• Junker, G. Supersymmetric Methods in Quantum and Statistical Physics, Springer-Verlag (1996).• Gordon L. Kane.Supersymmetry: Unveiling the Ultimate Laws of Nature Basic Books, New York (2001). ISBN

0-7382-0489-7.• Gordon L. Kane and Shifman, M., eds. The Supersymmetric World: The Beginnings of the Theory, World

Scientific, Singapore (2000). ISBN 981-02-4522-X.• D.V. Volkov, V.P. Akulov, Pisma Zh.Eksp.Teor.Fiz. 16 (1972) 621; Phys.Lett. B46 (1973) 109.• V.P. Akulov, D.V. Volkov, Teor.Mat.Fiz. 18 (1974) 39.• Weinberg, Steven, The Quantum Theory of Fields, Volume 3: Supersymmetry, Cambridge University Press,

Cambridge, (1999). ISBN 0-521-66000-9.• Wess, Julius, and Jonathan Bagger, Supersymmetry and Supergravity, Princeton University Press, Princeton,

(1992). ISBN 0-691-02530-4.• Bennett GW, et al.; Muon (g−2) Collaboration (2004). "Measurement of the negative muon anomalous magnetic

moment to 0.7 ppm". Physical Review Letters 92 (16): 161802. doi:10.1103/PhysRevLett.92.161802.PMID 15169217.

• Brookhaven National Laboratory (Jan. 8, 2004). New g−2 measurement deviates further from Standard Model(http:/ / www. bnl. gov/ bnlweb/ pubaf/ pr/ 2004/ bnlpr010804. htm). Press Release.

• Fermi National Accelerator Laboratory (Sept 25, 2006). Fermilab's CDF scientists have discovered thequick-change behavior of the B-sub-s meson. (http:/ / www. fnal. gov/ pub/ presspass/ press_releases/CDF_meson. html) Press Release.

External links• "Particle wobble shakes up supersymmetry" (http:/ / www. cosmosmagazine. com/ node/ 714), Cosmos magazine,

September 2006

Higgs boson 82

Higgs boson

Higgs boson

A simulated event, featuring the appearance of the Higgs boson

Composition: Elementary particle

Particle statistics: Bosonic

Status: Hypothetical

Theorized: F. Englert, R. Brout, P. Higgs, G. S. Guralnik, C. R. Hagen, and T. W. B. Kibble 1964

Mass: between 115 and 185 GeV/c2 (predicted)

Spin: 0

The Higgs boson is a hypothetical massive elementary particle predicted to exist by the Standard Model of particlephysics. The existence of the particle is postulated as a means of resolving inconsistencies in current theoreticalphysics, and attempts are being made to confirm the existence of the particle by experimentation, using the LargeHadron Collider (LHC) at CERN and the Tevatron at Fermilab.The Higgs boson is the only Standard Model particle that has not been observed in particle physics experiments. It isa consequence of the so-called Higgs mechanism which is the part of the Standard Model which explains how mostof the known elementary particles become massive.[1] For example, the Higgs boson would explain the differencebetween the massless photon, which mediates electromagnetism, and the massive W and Z bosons, which mediatethe weak force. If the Higgs boson exists, it is an integral and pervasive component of the material world.If it exists, it is of a class of particles known as scalar bosons. Bosons have integer spin, and scalar bosons have spin0. The photon is a kind of boson, and so is the less-familiar gluon, along with the W and Z particles mentionedabove. But these particles are all vector bosons, with spin 1. At present there are no known elementary scalar bosonsin nature, although many composite spin-0 particles are known.Theories exist that do not anticipate the Higgs boson, described elsewhere as Higgsless models. Relativelymodel-independent arguments suggest that any mechanism which generates the masses of the elementary particlesmust be visible below 1.4 TeV.[2] Therefore the Large Hadron Collider[3] is expected to provide experimentalevidence of the existence or non-existence of the Higgs boson. Experiments at Fermilab also continue previousattempts at detection, albeit hindered by the lower energy of the Tevatron accelerator, although it theoretically hasthe necessary energy to produce the Higgs boson.

Higgs boson 83

Origin of the theory

2010 APS J.J. Sakurai Prize Winners

When discussing the origin of the Higgs boson concept, it is importantto distinguish between the Higgs mechanism and the Higgs boson.

The Higgs mechanism (or"Englert-Brout-Higgs-Guralnik-Hagen-Kibble" [4] ) is a mechanism bywhich vector bosons can get a mass. It was proposed in 1964independently and almost simultaneously by three groups of physicists:François Englert and Robert Brout;,[5] by Peter Higgs,[6] (who wasinspired by the ideas of Philip Anderson); and by Gerald Guralnik, C.R. Hagen, and Tom Kibble,.[7]

The three papers written on this discovery by Guralnik, Hagen, Kibble, Higgs, Brout, and Englert were eachrecognized as milestone papers during Physical Review Letters 50th anniversary celebration.[8] While each of thesefamous papers took similar approaches, the contributions and differences between the 1964 PRL Symmetry Breakingpapers are noteworthy. These six physicists were also awarded the 2010 J. J. Sakurai Prize for Theoretical ParticlePhysics for this work.[9]

Steven Weinberg and Abdus Salam were the first to apply the Higgs mechanism to the electroweak symmetrybreaking. The Higgs mechanism not only explains how the electroweak vector bosons get a mass, but predicts theratio of the W boson and Z boson masses as well as their couplings among themselves and with the Standard Modelquarks and leptons. Many of these predictions have been verified by precise measurements performed at the LEP andthe SLC colliders, thus confirming that the Higgs mechanism takes place in nature.[10]

Out of the three seminal papers on the Higgs mechanism, only the paper by Peter Higgs mentioned, in a closingsentence, possible existence of the Higgs boson ("<...> an essential feature of the type of theory which has beendescribed in this note is the prediction of incomplete multiplets of scalar and vector bosons."). Peter Higgs added thissentence when he was revising the paper after it was rejected by Physics Letters, and before resubmitting it toPhysical Review Letters,.[11] The first detailed description of the Higgs boson properties was given in 1966, also byPeter Higgs,.[12]

In fact, the Higgs boson existence is not a strictly necessary consequence of the Higgs mechanism: the Higgs bosonexists in some but not all theories which use the Higgs mechanism. For example, Higgs boson exists in the StandardModel and the Minimal Supersymmetric Standard Model. Yet it is not expected to exist in Technicolor models or,more generally, Higgsless models. All of these models realize various forms of the Higgs mechanism. A major goalof the LHC experiments is to distinguish among these models and determine if the Higgs boson exists or not.

Theoretical overview

A one-loop Feynman diagram of the first-ordercorrection to the Higgs mass. The Higgs boson couples

strongly to the top quark so it may decay into topanti-top quark pairs if it is heavy enough.

The Higgs boson particle is one quantum component of thetheoretical Higgs field. In empty space, the Higgs field has anamplitude different from zero; i.e., a non-zero vacuum expectationvalue. The existence of this non-zero vacuum expectation plays afundamental role: it gives mass to every elementary particle thatcouples to the Higgs field, including the Higgs boson itself. Inparticular, the acquisition of a non-zero vacuum expectation valuespontaneously breaks electroweak gauge symmetry, whichscientists often refer to as the Higgs mechanism. This is thesimplest mechanism capable of giving mass to the gauge bosons

Higgs boson 84

while remaining compatible with gauge theories. In essence, this field is analogous to a pool of molasses that "sticks"to the otherwise massless fundamental particles that travel through the field, converting them into particles with massthat form, for example, the components of atoms. Prof. David J. Miller of University College London provided asimple explanation of the Higgs Boson, for which he won an award.[13]

In the Standard Model, the Higgs field consists of two neutral and two charged component fields. Both of thecharged components and one of the neutral fields are Goldstone bosons, which act as the longitudinalthird-polarization components of the massive W+, W–, and Z bosons. The quantum of the remaining neutralcomponent corresponds to the massive Higgs boson. Since the Higgs field is a scalar field, the Higgs boson has nospin, hence no intrinsic angular momentum. The Higgs boson is also its own antiparticle and is CP-even.The Standard Model does not predict the mass of the Higgs boson. If that mass is between 115 and 180 GeV/c2, thenthe Standard Model can be valid at energy scales all the way up to the Planck scale (1016 TeV). Many theoristsexpect new physics beyond the Standard Model to emerge at the TeV-scale, based on unsatisfactory properties of theStandard Model. The highest possible mass scale allowed for the Higgs boson (or some other electroweak symmetrybreaking mechanism) is 1.4 TeV; beyond this point, the Standard Model becomes inconsistent without such amechanism, because unitarity is violated in certain scattering processes. Many models of supersymmetry predict thatthe lightest Higgs boson (of several) will have a mass only slightly above the current experimental limits, at around120 GeV or less.Supersymmetric extensions of the Standard Model (so called SUSY) predict the existence of whole families of Higgsbosons, as opposed to a single Higgs particle of the Standard Model. Among the SUSY models, in the MinimalSupersymmetric extension (MSSM) the Higgs mechanism yields the smallest number of Higgs bosons: there are twoHiggs doublets, leading to the existence of a quintet of scalar particles: two CP-even neutral Higgs bosons h and H, aCP-odd neutral Higgs boson A, and two charged Higgs particles H±.There are over a hundred theoretical Higgs-mass predictions.[14]

Experimental search

Status as of August 2010, to 95% confidence interval

As of December 2010, the Higgs bosonhas yet to be confirmedexperimentally,[15] despite large effortsinvested in accelerator experiments atCERN and Fermilab.

Prior to the year 2000, the datagathered at the LEP collider at CERNallowed an experimental lower bound to be set for the mass of the Standard Model Higgs boson of 114.4 GeV/c2 at95% confidence level. The same experiment has produced a small number of events that could be interpreted asresulting from Higgs bosons with mass just above said cutoff—around 115 GeV—but the number of events wasinsufficient to draw definite conclusions.[16] The LEP

Higgs boson 85

A Feynman diagram of one way the Higgs boson maybe produced at the LHC. Here, two gluons decay into atop/anti-top pair, which then combine to make a neutral

Higgs.

A Feynman diagram of another way the Higgs bosonmay be produced at the LHC. Here, two quarks each

emit a W or Z boson, which combine to make a neutralHiggs.

was shut down in 2000 due to construction of its successor, theLarge Hadron Collider which is expected to be able to confirm orreject the existence of the Higgs boson. Full operational mode wasdelayed until mid-November 2009, because of a serious faultdiscovered with a number of magnets during the calibration andstartup phase.[17] [18]

At the Fermilab Tevatron, there are ongoing experimentssearching for the Higgs boson. As of July 2010, combined datafrom CDF and DØ experiments at the Tevatron were sufficient toexclude the Higgs boson in the range between 158 GeV/c2 and175 GeV/c2 at the 95% confidence level.[19] [20] Data collectionand analysis in search of Higgs are intensifying since March 30,2010 when the LHC began operating at 3.5 Tev and is rapidlyapproaching in its design range of 7 Tev, well above that at whichdetection should occur.[21]

It may be possible to estimate the mass of the Higgs boson indirectly. In the Standard Model, the Higgs boson has anumber of indirect effects; most notably, Higgs loops result in tiny corrections to masses of W and Z bosons.Precision measurements of electroweak parameters, such as the Fermi constant and masses of W/Z bosons, can beused to constrain the mass of the Higgs. As of 2006, measurements of electroweak observables allowed the exclusionof a Standard Model Higgs boson having a mass greater than 285 GeV/c2 at 95% CL, and estimated its mass to be129  GeV/c2 (the central value corresponds to approximately 138 proton masses).[22] As of August 2009, theStandard Model Higgs boson is excluded by electroweak measurements above 186 GeV at 95% CL. However, itshould be noted that these indirect constraints make the assumption that the Standard Model is correct. One may stilldiscover a Higgs boson above 186 GeV if it is accompanied by other particles between Standard Model and GUTscales.Some have argued that there already exists potential evidence,[23] [24] [25] but to date no such evidence has convincedthe physics community.In a 2009 preprint,[26] it was suggested (and reported under headlines such as Higgs could reveal itself inDark-Matter collisions[27] ) that the Higgs Boson might not only interact with the above-mentioned particles of theStandard model of particle physics, but also with the mysterious WIMPs ("weakly interacting massive particles") ofthe Dark matter, playing a most-important role in recent astrophysics. In this case, it is natural to augment the aboveFeynman diagrams by terms representing such an interaction.

Higgs boson 86

In principle, a relation between the Higgs particle and the Dark matter would be "not unexpected", since, (i), theHiggs field does not directly couple to the quanta of light (i.e. the photons), while at the same time, (ii), it generatesmass. However, "dark matter" is a metonym for the discrepancy between the apparent observed mass of the universeand that given by the standard model and is not a component of any known theory of physics. Consequently, theusefulness of this conjecture is limited.Barring discovery during current intensive efforts, it will be sometime after the end of the current physics fill at theLHC in 2011 and some further months or years of analysis of the collected data before scientists can confidentlybelieve that the Higgs Boson does not exist.

Alternatives for electroweak symmetry breakingIn the years since the Higgs boson was proposed, several alternatives to the Higgs mechanism have been proposed.All of the alternative mechanisms use strongly interacting dynamics to produce a vacuum expectation value thatbreaks electroweak symmetry. A partial list of these alternative mechanisms are• Technicolor[28] is a class of models that attempts to mimic the dynamics of the strong force as a way of breaking

electroweak symmetry.• Extra dimensional Higgsless models where the role of the Higgs field is played by the fifth component of the

gauge field.[29]

• Abbott-Farhi models of composite W and Z vector bosons.[30]

• Top quark condensate.• Braid model of Standard Model particles by Sundance Bilson-Thompson, compatible with loop quantum gravity

and similar theories.[31]

"The God particle"The Higgs boson is often referred to as "the God particle" by the media,[32] after the title of Leon Lederman's book,The God Particle: If the Universe Is the Answer, What Is the Question?.[33] While use of this term may havecontributed to increased media interest in particle physics and the Large Hadron Collider,[33] many scientists dislikeit.[32] In a renaming competition, a jury of physicists chose the name "the champagne bottle boson" as the bestpopular name.[34]

See also• Higgs boson in fiction• Higgs mechanism• List of particles• Overview and Differences of 1964 PRL Symmetry Breaking papers• Quantum triviality• Yukawa interaction• ZZ diboson

Higgs boson 87

Notes[1] The masses of composite particles such as the proton and neutron would only be partly due to the Higgs Mechanism and are already

understood as a consequence of the strong interaction.[2] Lee, Benjamin W.; Quigg, C.; Thacker, H. B. (1977). "Weak interactions at very high energies: The role of the Higgs-boson mass". Phys.

Rev. D 16: 1519–1531. doi:10.1103/PhysRevD.16.1519.[3] "Huge $10 billion collider resumes hunt for 'God particle' - CNN.com" (http:/ / www. cnn. com/ 2009/ TECH/ 11/ 11/ lhc. large. hadron.

collider. beam/ index. html). CNN. 2009-11-11. . Retrieved 2010-05-04.[4] Englert-Brout-Higgs-Guralnik-Hagen-Kibble Mechanism on Scholarpedia (http:/ / www. scholarpedia. org/ article/

Englert-Brout-Higgs-Guralnik-Hagen-Kibble_mechanism)[5] Englert, François; Brout, Robert (1964). "Broken Symmetry and the Mass of Gauge Vector Mesons". Physical Review Letters 13: 321–23.

doi:10.1103/PhysRevLett.13.321[6] Higgs, Peter (1964). "Broken Symmetries and the Masses of Gauge Bosons". Physical Review Letters 13: 508–509.

doi:10.1103/PhysRevLett.13.508[7] Guralnik, Gerald; Hagen, C. R.; Kibble, T. W. B. (1964). "Global Conservation Laws and Massless Particles". Physical Review Letters 13:

585–587. doi:10.1103/PhysRevLett.13.585[8] Physical Review Letters - 50th Anniversary Milestone Papers (http:/ / prl. aps. org/ 50years/ milestones#1964). Physical Review Letters.[9] "American Physical Society - J. J. Sakurai Prize Winners" (http:/ / www. aps. org/ units/ dpf/ awards/ sakurai. cfm).[10] "LEP Electroweak Working Group" (http:/ / lepewwg. web. cern. ch/ LEPEWWG/ ).[11] Higgs, Peter (2007). "Prehistory of the Higgs boson". Comptes Rendus Physique 8: 970–972. doi:10.1016/j.crhy.2006.12.006[12] Higgs, Peter (1966). "Spontaneous Symmetry Breakdown without Massless Bosons". Physical Review 145: 1156–1163.

doi:10.1103/PhysRev.145.1156[13] A quasi-political Explanation of the Higgs Boson; for Mr Waldegrave, UK Science Minister 1993 (http:/ / www. hep. ucl. ac. uk/ ~djm/

higgsa. html)[14] T. Schücker (2007). "Higgs-mass predictions". arΧiv:0708.3344 [hep-ph].[15] Scientists present first “bread-and-butter” results from LHC collisions (http:/ / www. symmetrymagazine. org/ breaking/ 2010/ 06/ 08/

scientists-present-first-bread-and-butter-results-from-lhc-collisions/ ) Symmetry Breaking, 8 June 2010[16] W.-M. Yao et al. (2006). Searches for Higgs Bosons "Review of Particle Physics" (http:/ / pdg. lbl. gov/ 2006/ reviews/ higgs_s055. pdf).

Journal of Physics G 33: 1. doi:10.1088/0954-3899/33/1/001. Searches for Higgs Bosons.[17] "CERN management confirms new LHC restart schedule" (http:/ / press. web. cern. ch/ press/ PressReleases/ Releases2009/ PR02. 09E.

html). CERN Press Office. 9 February 2009. . Retrieved 2009-02-10.[18] "CERN reports on progress towards LHC restart" (http:/ / press. web. cern. ch/ press/ PressReleases/ Releases2009/ PR09. 09E. html).

CERN Press Office. 19 June 2009. . Retrieved 2009-07-21.[19] T. Aaltonen et al. (CDF and DØ Collaborations) (2010). "Combination of Tevatron searches for the standard model Higgs boson in the

W+W− decay mode". arΧiv:1001.4162 [hep-ex].[20] "Fermilab experiments narrow allowed mass range for Higgs boson" (http:/ / www. fnal. gov/ pub/ presspass/ press_releases/

Higgs-mass-constraints-20100726-images. html). Fermilab. 26 July 2010. . Retrieved 2010-07-26.[21] CERN Bulletin Issue No. 18-20/2010 - Monday 3 May 2010 (http:/ / cdsweb. cern. ch/ journal/ CERNBulletin/ 2010/ 18/ News Articles/

1262593?ln=en)[22] " H0 Indirect Mass Limits from Electroweak Analysis. (http:/ / pdglive. lbl. gov/ popupblockdata. brl?nodein=S055HEW& inscript=Y&

fsizein=1)"[23] Potential Higgs Boson discovery: " Higgs Boson: Glimpses of the God particle. (http:/ / www. newscientist. com/ channel/ fundamentals/

mg19325934. 600-higgs-boson-glimpses-of-the-god-particle. html)" New Scientist, 02 March 2007[24] " 'God particle' may have been seen, (http:/ / news. bbc. co. uk/ 2/ hi/ science/ nature/ 3546973. stm)" BBC news, 10 March 2004.[25] US experiment hints at 'multiple God particles' (http:/ / news. bbc. co. uk/ 1/ hi/ science_and_environment/ 10313875. stm) BBC News 14

June 2010[26] arXiv:0912.0004 Higgs in Space! (http:/ / arxiv. org/ abs/ 0912. 0004)[27] Physics World, (http:/ / physicsworld. com/ cws/ article/ news/ 41218), a website supported by the British Institute of Physics[28] S. Dimopoulos and Leonard Susskind (1979). "Mass Without Scalars". Nuclear Physics B 155: 237–252.

doi:10.1016/0550-3213(79)90364-X.[29] C. Csaki and C. Grojean and L. Pilo and J. Terning (2004). "Towards a realistic model of Higgsless electroweak symmetry breaking".

Physical Review Letters 92: 101802. doi:10.1103/PhysRevLett.92.101802. arXiv:hep-ph/0308038.[30] L. F. Abbott and E. Farhi (1981). "Are the Weak Interactions Strong?". Physics Letters B 101: 69. doi:10.1016/0370-2693(81)90492-5.[31] Bilson-Thompson, Sundance O.; Markopoulou, Fotini; Smolin, Lee (2007). "Quantum gravity and the standard model". Class. Quantum

Grav. 24 (16): 3975–3993. doi:10.1088/0264-9381/24/16/002. arXiv:hep-th/0603022.[32] Ian Sample (29 May 2009). "Anything but the God particle" (http:/ / www. guardian. co. uk/ science/ blog/ 2009/ may/ 29/

why-call-it-the-god-particle-higgs-boson-cern-lhc). London: The Guardian. . Retrieved 2009-06-24.[33] Ian Sample (3 March 2009). "Father of the God particle: Portrait of Peter Higgs unveiled" (http:/ / www. guardian. co. uk/ science/ blog/

2009/ mar/ 02/ god-particle-peter-higgs-portrait-lhc). London: The Guardian. . Retrieved 2009-06-24.

Higgs boson 88

[34] Sample, Ian (2009-06-12). "Higgs competition: Crack open the bubbly, the God particle is dead" (http:/ / www. guardian. co. uk/ science/blog/ 2009/ jun/ 05/ cern-lhc-god-particle-higgs-boson). The Guardian (London). . Retrieved 2010-05-04.

References• " The LEP Electroweak Working Group. (http:/ / lepewwg. web. cern. ch/ LEPEWWG/ )"• " Particle Data Group: Review of searches for Higgs bosons. (http:/ / pdg. lbl. gov/ 2005/ reviews/

contents_sports. html#hyppartetc)"• Leon Lederman and Dick Teresi, 1993. The God Particle: If the Universe Is the Answer, What Is the Question?

Houghton Mifflin Co. ISBN 0-395-55849-2, paperback ISBN 0-385-31211-3.• " Fermilab Results Change Estimated Mass Of Postulated Higgs boson. (http:/ / www. spacedaily. com/ news/

physics-04s. html)"• " Higgs boson on the horizon. (http:/ / physicsweb. org/ article/ news/ 4/ 9/ 2/ 1)"• " Signs of mass-giving particle get stronger. (http:/ / www. sciencenews. org/ articles/ 20001104/ fob6. asp)"• " Higgs boson: One page explanation. (http:/ / www. phy. uct. ac. za/ courses/ phy400w/ particle/ higgs. htm)" In

1993, the UK Science Minister, William Waldegrave, challenged physicists to produce a one page answer to thequestion "What is the Higgs boson, and why do we want to find it?"

• " Higgs mechanism/boson simple explanation via cartoon. (http:/ / www. pparc. ac. uk/ ps/ bbs/ bbs_mass_hm.asp)"

• " Higgs physics at the LHC. (http:/ / www. quark. lu. se/ ~atlas/ thesis/ egede/ thesis-node6. html)"• " Quark experiment predicts heavier Higgs. (http:/ / www. newscientist. com/ news/ news. jsp?id=ns99995095)"• Martin, Richard, " The God Particle and the Grid. (http:/ / www. wired. com/ wired/ archive/ 12. 04/ grid_pr.

html)"• " The Higgs boson (http:/ / www. exploratorium. edu/ origins/ cern/ ideas/ higgs. html)" by the CERN

exploratorium.• " Higgs Boson - the search for the God particle. (http:/ / www. bbc. co. uk/ radio4/ history/ inourtime/

inourtime_20041118. shtml)" BBC Radio 4: "In Our Time"

Further reading• G.S. Guralnik, C.R. Hagen and T.W.B. Kibble (1964). "Global Conservation Laws and Massless Particles".

Physical Review Letters 13: 585. doi:10.1103/PhysRevLett.13.585.• G.S. Guralnik (2009). "The History of the Guralnik, Hagen and Kibble development of the Theory of

Spontaneous Symmetry Breaking and Gauge Particles". International Journal of Modern Physics A 24:2601–2627. doi:10.1142/S0217751X09045431. arXiv:0907.3466.

• F. Englert and R. Brout (1964). "Broken Symmetry and the Mass of Gauge Vector Mesons". Physical ReviewLetters 13: 321. doi:10.1103/PhysRevLett.13.321.

• P. Higgs (1964). "Broken Symmetries, Massless Particles and Gauge Fields". Physics Letters 12: 132.doi:10.1016/0031-9163(64)91136-9.

• P. Higgs (1964). "Broken Symmetries and the Masses of Gauge Bosons". Physical Review Letters 13: 508.doi:10.1103/PhysRevLett.13.508.

• P. Higgs (1966). "Spontaneous Symmetry Breakdown without Massless Bosons". Physical Review 145: 1156.doi:10.1103/PhysRev.145.1156.

• Y. Nambu and G. Jona-Lasinio (1961). "Dynamical Model of Elementary Particles Based on an Analogy withSuperconductivity". Physical Review 122: 345–358. doi:10.1103/PhysRev.122.345.

• J. Goldstone, A. Salam and S. Weinberg (1962). "Broken Symmetries". Physical Review 127: 965.doi:10.1103/PhysRev.127.965.

• P.W. Anderson (1963). "Plasmons, Gauge Invariance, and Mass". Physical Review 130: 439.doi:10.1103/PhysRev.130.439.

Higgs boson 89

• A. Klein and B.W. Lee (1964). "Does Spontaneous Breakdown of Symmetry Imply Zero-Mass Particles?".Physical Review Letters 12: 266. doi:10.1103/PhysRevLett.12.266.

• W. Gilbert (1964). "Broken Symmetries and Massless Particles". Physical Review Letters 12: 713.doi:10.1103/PhysRevLett.12.713.

External links• Explanation for beginners (http:/ / cms. web. cern. ch/ cms/ Physics/ HuntingHiggs/ index. html)• At Fermilab, the Race Is on for the 'God Particle' (http:/ / www. nytimes. com/ 2007/ 07/ 24/ science/ 24ferm.

html)• Physics World, Introducing the little Higgs (http:/ / physicsworld. com/ cws/ article/ print/ 11353)• A quasi-political Explanation of the Higgs Boson (http:/ / www. hep. ucl. ac. uk/ ~djm/ higgsa. html)• The Atom Smashers, a blog about the making of a documentary about the search for the Higgs boson (http:/ /

www. theatomsmashers. blogspot. com/ )• In CERN Courier, Steven Weinberg reflects on spontaneous symmetry breaking (http:/ / cerncourier. com/ cws/

article/ cern/ 32522)• Steven Weinberg Praises Teams for Higgs Boson Theory (http:/ / www. pas. rochester. edu/ urpas/ news/

Hagen_030708)• Steven Weinberg on LHC (http:/ / www. youtube. com/ watch?v=Zl4W3DYTIKw)• Physical Review Letters - 50th Anniversary Milestone Papers (http:/ / prl. aps. org/ 50years/ milestones#1964)• Imperial College London on PRL 50th Anniversary Milestone Papers (http:/ / www3. imperial. ac. uk/

newsandeventspggrp/ imperialcollege/ newssummary/ news_13-6-2008-12-42-20?newsid=38514)• The God Particle, from National Geographic Magazine (http:/ / ngm. nationalgeographic. com/ 2008/ 03/

god-particle/ achenbach-text)• "Tevatron experiments double-team Higgs boson", sets lower bound at 170GeV (http:/ / www. physorg. com/

news137076565. html)• The History of the Guralnik, Hagen and Kibble development of the Theory of Spontaneous Symmetry Breaking

and Gauge Particles (http:/ / arxiv. org/ abs/ 0907. 3466)• The History of the Guralnik, Hagen and Kibble development of the Theory of Spontaneous Symmetry Breaking

and Gauge Particles (PDF) (http:/ / arxiv. org/ abs/ 0907. 3466v1)• Englert-Brout-Higgs-Guralnik-Hagen-Kibble Mechanism on Scholarpedia (http:/ / www. scholarpedia. org/

article/ Englert-Brout-Higgs-Guralnik-Hagen-Kibble_mechanism)• History of Englert-Brout-Higgs-Guralnik-Hagen-Kibble Mechanism on Scholarpedia (http:/ / www. scholarpedia.

org/ article/ Englert-Brout-Higgs-Guralnik-Hagen-Kibble_mechanism_(history))• Sakurai Prize Videos (http:/ / www. youtube. com/ view_play_list?p=BDA16F52CA3C9B1D)• God Particle Overview (http:/ / www. godparticle. com/ )• Fermilab 'closing in' on the God particle (http:/ / www. newscientist. com/ article/

dn16618-fermilab-closing-in-on-the-god-particle. html)• The Hunt for the Higgs at Tevatron (http:/ / apps3. aps. org/ aps/ meetings/ april10/ roser. pdf)• Artist's vision of Higgs boson by a Prague based fine art photographer Jan Krasňan (from his series created in

January 2009) (http:/ / krasnan. com/ abstract. pdf)• In Our Time:Higgs Boson (http:/ / www. bbc. co. uk/ programmes/ p004y2b7) BBC Radio 4 programme

90

Safety

Safety of particle collisions at the Large HadronCollider

A simulated particle collision in the LHC.

The safety of particle collisions at the Large HadronCollider has been questioned in the media, on theInternet and through the courts. Particle physicsexperiments were ongoing as of March 2010 at theLarge Hadron Collider (LHC), the world's largest andmost powerful particle accelerator, built by theEuropean Organization for Nuclear Research (CERN)near Geneva, in Switzerland.[1] [2] The claimed dangersof the LHC particle collisions, which began inNovember 2009, include doomsday scenarios involvingthe production of stable micro black holes and thecreation of hypothetical particles called strangelets.[3]

To address such concerns, CERN mandated a group ofindependent scientists to review these scenarios. In areport issued in 2003, they concluded that, like currentparticle experiments such as the Relativistic Heavy IonCollider (RHIC), the LHC particle collisions pose no conceivable threat.[4] A second review of the evidencecommissioned by CERN was released in 2008. The report, prepared by a group of physicists affiliated to CERN butnot involved in the LHC experiments, reaffirmed the safety of the LHC collisions in light of further researchconducted since the 2003 assessment.[5] [6] It was reviewed and endorsed by a CERN committee of 20 externalscientists and by the Executive Committee of the Division of Particles & Fields of the American Physical Society,[7]

[8] and was later published in the peer-reviewed Journal of Physics G by the UK Institute of Physics, which alsoendorsed its conclusions.[5] [9] The report ruled out any doomsday scenario at the LHC: the physical conditions andevents that will be created in the LHC experiments occur naturally in the universe without hazardousconsequences.[5]

Safety of particle collisions at the Large Hadron Collider 91

Particle accelerator

The LHC's CMS detector.

The Large Hadron Collider (LHC) is the world's largest and highest-energyparticle accelerator complex, intended to collide opposing beams of eitherprotons or lead nuclei with very high kinetic energy.[10] [11] It was built by theEuropean Organization for Nuclear Research (CERN) near Geneva, inSwitzerland. The LHC's main purpose is to explore the validity and limitations ofthe Standard Model, the current theoretical picture for particle physics. The firstparticle collisions at the LHC took place shortly after startup in November 2009,at energies up to 1.2 TeV per beam.[12] .

On 30 March 2010, the first planned collisions took place between two 3.5 TeVbeams, which set another new world record for the highest energy man-madeparticle collisions.[13]

Due to problematic connections between the superconducting magnets that guidethe beams, the LHC will not run at its designed 7 TeV per beam (14 TeVcenter-of-mass) until after a long shutdown that is scheduled to begin at the end of 2011.[14]

Safety concernsIn the run up to the commissioning of the LHC, Walter L. Wagner (an original opponent of the RHIC), Luis Sancho(a Spanish science writer) and Otto Rössler (a German biochemist) have expressed concerns over the safety of theLHC, and have attempted to halt the beginning of the experiments through petitions to the US and EuropeanCourts.[1] [15] [16] [17] [18] These opponents assert that the LHC experiments have the potential to create low velocitymicro black holes that could grow in mass or release dangerous radiation leading to doomsday scenarios, such as thedestruction of the Earth.[3] [19] Other claimed potential risks include the creation of theoretical particles calledstrangelets, magnetic monopoles and vacuum bubbles.[3] [19]

Based on such safety concerns, US federal judge Richard Posner[20] , Future of Humanity Institute research associateToby Ord[21] and others[22] [23] [24] [25] have argued that the LHC experiments are too risky to undertake. In the bookOur Final Century: Will the Human Race Survive the Twenty-first Century?, English cosmologist and astrophysicistMartin Rees calculated an upper limit of 1 in 50 million for the probability that the Large Hadron Collider willproduce a global catastrophe or black hole.[15] However, Rees has also reported not to be "losing sleep over thecollider," and trusts the scientists who have built it.[26] He has stated: "My book has been misquoted in one or twoplaces. I would refer you to the up-to-date safety study."[27]

These risk assessments of catastrophic scenarios at the LHC have sparked fears among the public,[1] and scientistsassociated with the project have received protests. The Large Hadron Collider team revealed that they had receiveddeath threats and threatening emails and phone calls demanding the experiment be halted.[27] On 9 September 2008,Romania's Conservative Party held a protest before the European Commission mission to Bucharest, demanding thatthe experiment be halted because it feared that the LHC could create dangerous black holes.[28] [29]

Media coverage of safety concernsThe safety concerns regarding the LHC collisions have attracted widespread media attention.[1] [30] Various widely circulated newspapers have reported doomsday fears in connection with the collider, including The Times,[31] The Guardian,[32] The Independent,[33] The Sydney Morning Herald,[34] and Time.[35] Among other media sources, CNN mentioned that "Some have expressed fears that the project could lead to the Earth's demise,"[36] but it assured its readers with comments from scientists like John Huth, who said that it was "baloney".[36] MSNBC said that, "there are more serious things to worry about"[37] and allayed fears that "the atom-smasher might set off earthquakes or

Safety of particle collisions at the Large Hadron Collider 92

other dangerous rumblings".[37] The results of an online survey it conducted "indicate that a lot of [the public] knowenough not to panic".[37] The BBC stated, "the scientific consensus appears to be on the side of CERN's theorists"[38]

who say the LHC has "no conceivable danger".[38] Brian Greene in the New York Times reassured readers bysaying,"If a black hole is produced under Geneva, might it swallow Switzerland and continue on a ravenous rampageuntil the Earth is devoured? It’s a reasonable question with a definite answer: no."[39]

The tabloids also covered the safety concerns. The Daily Mail produced headlines such as "Are we all going to dienext Wednesday?"[40] and "End of the world postponed as broken Hadron Collider out of commission until thespring"[41] . The Sun quoted Otto Rössler saying, "The weather will change completely, wiping out life. There willbe a Biblical Armageddon."[42] After the launch of the collider, it had a story entitled, "Success! The world hasn'tended".[43]

On 10 September 2008, a 16-year-old girl from Sarangpur, Madhya Pradesh, India committed suicide, havingbecome distressed about predictions of an impending "doomsday" made on an Indian news channel (Aaj Tak)covering the LHC.[44]

After the dismissal of the federal lawsuit, The Daily Show's correspondent John Oliver interviewed Walter L.Wagner, who declared that he believed the chance of the LHC destroying the Earth to be 50%, since it will eitherhappen or it won't.[45] [46]

Safety reviewsConcerns similar to those for the LHC were raised in connection with the RHIC particle accelerator.[47] [48] [49] [50]

After detailed studies, scientists reached such conclusions as "beyond reasonable doubt, heavy-ion experiments atRHIC will not endanger our planet"[51] and that there is "powerful empirical evidence against the possibility ofdangerous strangelet production."[52]

CERN-commissioned reportsDrawing from research performed to assess the safety of the RHIC collisions, the LHC Safety Study Group, a groupof independent scientists, performed a safety analysis of the LHC, and released their findings in the 2003 reportStudy of Potentially Dangerous Events During Heavy-Ion Collisions at the LHC. The report concluded that there is"no basis for any conceivable threat".[4] Several of its arguments were based on the predicted evaporation ofhypothetical micro black holes by Hawking radiation and on the theoretical predictions of the Standard Model withregard to the outcome of events to be studied in the LHC. One argument raised against doomsday fears was thatcollisions at energies equivalent to and higher than those of the LHC have been happening in nature for billions ofyears apparently without hazardous effects, as ultra-high-energy cosmic rays impact Earth's atmosphere and otherbodies in the universe.[4]

In 2007, CERN mandated a group of five particle physicists not involved in the LHC experiments — the LHC SafetyAssessment Group (LSAG), consisting of John Ellis, Gian Giudice, Michelangelo Mangano and Urs Wiedemann, ofCERN, and Igor Tkachev, of the Institute for Nuclear Research in Moscow — to monitor the latest concerns aboutthe LHC collisions.[6] On 20 June 2008, in light of new experimental data and theoretical understanding, the LSAGissued a report updating the 2003 safety review, in which they reaffirmed and extended its conclusions that "LHCcollisions present no danger and that there are no reasons for concern".[5] [6] The LSAG report was then reviewed byCERN’s Scientific Policy Committee (SPC), a group of external scientists that advises CERN’s governing body, itsCouncil.[7] [17] [53] The report was reviewed and endorsed by a panel of five independent scientists, PeterBraun-Munzinger, Matteo Cavalli-Sforza, Gerard 't Hooft, Bryan Webber and Fabio Zwirner, and their conclusionswere unanimously approved by the full 20 members of the SPC.[53] On 5 September 2008, the LSAG's "Review ofthe safety of LHC collisions" was published in the Journal of Physics G: Nuclear and Particle Physics by the UKInstitute of Physics, which endorsed its conclusions in a press release that announced the publication.[5] [9]

Safety of particle collisions at the Large Hadron Collider 93

Following the July 2008 release of the LSAG safety report,[5] the Executive Committee of the Division of Particlesand Fields (DPF) of the American Physical Society, the world's second largest organization of physicists, issued astatement approving the LSAG's conclusions and noting that "this report explains why there is nothing to fear fromparticles created at the LHC".[8] On 1 August 2008, a group of German quantum physicists, the Committee forElementary Particle Physics (KET),[54] published an open letter further dismissing concerns about the LHCexperiments and carrying assurances that they are safe based on the LSAG safety review.[2] [55]

Other publicationsOn 20 June 2008, Steven Giddings and Michelangelo Mangano issued a research paper titled the "Astrophysicalimplications of hypothetical stable TeV-scale black holes", where they develop arguments to exclude any risk ofdangerous black hole production at the LHC.[56] On 18 August 2008, this safety review was published in thePhysical Review D,[57] and a commentary article which appeared the same day in the journal Physics endorsedGiddings' and Mangano's conclusions.[58] The LSAG report draws heavily on this research.[17]

On 9 February 2009, a paper titled "Exclusion of black hole disaster scenarios at the LHC" was published in thejournal Physics Letters B.[59] The article, which summarizes proofs aimed at ruling out any possible black holedisaster at the LHC, relies on a number of new safety arguments as well as certain arguments already present inGiddings' and Mangano's paper "Astrophysical implications of hypothetical stable TeV-scale black holes".[56]

Safety arguments

Micro black holesAlthough the Standard Model of particle physics predicts that LHC energies are far too low to create black holes,some extensions of the Standard Model posit the existence of extra spatial dimensions, in which it would be possibleto create micro black holes at the LHC at a rate of the order of one per second.[60] [61] [62] [63] [64] According to thestandard calculations these are harmless because they would quickly decay by Hawking radiation.[62] Hawkingradiation is a thermal radiation predicted to be emitted by black holes due to quantum effects. Because Hawkingradiation allows black holes to lose mass, black holes that lose more matter than they gain through other means areexpected to dissipate, shrink, and ultimately vanish. Smaller micro black holes (MBHs), which could be produced atthe LHC, are currently predicted by theory to be larger net emitters of radiation than larger black holes, and to shrinkand dissipate instantly.[65] The LHC Safety Assessment Group (LSAG) indicates that "there is broad consensusamong physicists on the reality of Hawking radiation, but so far no experiment has had the sensitivity required tofind direct evidence for it."[5]

According to the LSAG, even if micro black holes were produced by the LHC and were stable, they would be unableto accrete matter in a manner dangerous for the Earth. They would also have been produced by cosmic rays and havestopped in neutron stars and white dwarfs, and the stability of these astronomical bodies means that they cannot bedangerous:[5] [66]

Stable black holes could be either electrically charged or neutral. [...] If stable microscopic black holes had noelectric charge, their interactions with the Earth would be very weak. Those produced by cosmic rays wouldpass harmlessly through the Earth into space, whereas those produced by the LHC could remain on Earth.However, there are much larger and denser astronomical bodies than the Earth in the Universe. Black holesproduced in cosmic-ray collisions with bodies such as neutron stars and white dwarf stars would be brought torest. The continued existence of such dense bodies, as well as the Earth, rules out the possibility of the LHCproducing any dangerous black holes.[6]

Safety of particle collisions at the Large Hadron Collider 94

StrangeletsStrangelets are small fragments of strange matter—a hypothetical form of quark matter—that contain roughly equalnumbers of up, down, and strange quarks and that are more stable than ordinary nuclei (strangelets would range insize from a few femtometers to a few meters across).[5] If strangelets can actually exist, and if they were produced atthe LHC, they could conceivably initiate a runaway fusion process in which all the nuclei in the planet would beconverted to strange matter, similar to a strange star.[5]

The probability of the creation of strangelets decreases at higher energies.[5] As the LHC operates at higher energiesthan the RHIC or the heavy ion programs of the 1980s and 1990s, the LHC is less likely to produce strangelets thanits predecessors.[5] Furthermore, models indicate that strangelets are only stable or long-lived at low temperatures.Strangelets are bound at low energies (in the range of 1–10 MeV), while the collisions in the LHC release energies inthe range of 14 TeV. The second law of thermodynamics precludes the formation of a cold condensate that is anorder of magnitude cooler than the surrounding medium. This can be illustrated by the example of trying to form anice cube in boiling water.[5]

Specific concerns and responsesOtto Rössler, a German chemistry professor at the University of Tübingen, argues that micro black holes created inthe LHC could grow exponentially.[67] [68] [69] [70] [71] On 4 July 2008, Rössler met with a CERN physicist, RolfLandua, with whom he discussed his safety concerns.[72] Following the meeting, Landua asked another expert,Hermann Nicolai, Director of the Albert Einstein Institute, in Germany, to examine Rössler's arguments.[72] Nicolaireviewed Otto Rössler's research paper on the safety of the LHC[68] and issued a statement highlighting logicalinconsistencies and physical misunderstandings in Rössler's arguments.[73] Nicolai concluded that "this text wouldnot pass the referee process in a serious journal."[71] [73] Domenico Giulini also commented with Hermann Nicolaion Otto Rössler's thesis, concluding that "his argument concerns only the General Theory of Relativity (GRT), andmakes no logical connection to LHC physics; the argument is not valid; the argument is not self-consistent."[74] On 1August 2008, a group of German physicists, the Committee for Elementary Particle Physics (KET),[54] published anopen letter further dismissing Rössler's concerns and carrying assurances that the LHC is safe.[2] [55] Otto Rösslerwas due to meet Swiss president Pascal Couchepin in August 2008 to discuss this concern,[75] but it was laterreported that the meeting had been canceled as it was believed Rössler and his fellow opponents would have used themeeting for their own publicity.[76]

On 10 August 2008, Rainer Plaga, a German astrophysicist, posted a research paper on the arXiv Web archiveconcluding that LHC safety studies have not definitely ruled out the potential catastrophic threat from microscopicblack holes, including the possible danger from Hawking radiation emitted by black holes.[3] [77] [78] [79] In afollow-up paper posted on the arXiv on 29 August 2008, Steven Giddings and Michelangelo Mangano, the authorsof the research paper "Astrophysical implications of hypothetical stable TeV-scale black holes",[56] responded toPlaga's concerns.[80] They pointed out what they see as a basic inconsistency in Plaga's calculation, and argued thattheir own conclusions on the safety of the collider, as referred to in the LHC safety assessment (LSAG) report,[5]

remain robust.[80] Giddings and Mangano also referred to the research paper "Exclusion of black hole disasterscenarios at the LHC", which relies on a number of new arguments to conclude that there is no risk due to mini blackholes at the LHC.[3] [59] . On 19 January 2009 Roberto Casadio, Sergio Fabi and Benjamin Harms posted on thearXiv a paper, later published on Physical Review D, ruling out the catastrophic growth of black holes in the scenarioconsidered by Plaga.[81] In reaction to the criticisms, Plaga updated his paper on the arXiv on 26 September 2008and again on 9 August 2009.[77] So far, Plaga's paper has not been published in a peer-reviewed journal.

Safety of particle collisions at the Large Hadron Collider 95

Legal challengesOn 21 March 2008, a complaint requesting an injunction to halt the LHC's startup was filed by Walter L. Wagnerand Luis Sancho against CERN and its American collaborators, the US Department of Energy, the National ScienceFoundation and the Fermi National Accelerator Laboratory, before the United States District Court for the District ofHawaii.[19] [82] [83] The plaintiffs demanded an injunction against the LHC's activation for 4 months after issuance ofthe LHC Safety Assessment Group's (LSAG) most recent safety documentation, and a permanent injunction until theLHC can be demonstrated to be reasonably safe within industry standards.[84] The US Federal Court scheduled trialto begin 16 June 2009.[85]

The LSAG review, issued on 20 June 2008 after outside review, found "no basis for any concerns about theconsequences of new particles or forms of matter that could possibly be produced by the LHC".[5] The USGovernment, in response, called for summary dismissal of the suit against the government defendants as untimelydue to the expiration of a six-year statute of limitations (since funding began by 1999 and has essentially beencompleted already), and also called the hazards claimed by the plaintiffs "overly speculative and not credible".[86]

The Hawaii District Court heard the government's motion to dismiss on 2 September 2008,[1] and on 26 Septemberthe Court issued an order granting the motion to dismiss on the grounds that it had no jurisdiction over the LHCproject.[87] A subsequent appeal by the plaintiffs was dismissed by the Court on 24 August 2010.[88]

On 26 August 2008, a group of European citizens, led by a German biochemist Otto Rössler, filed a suit againstCERN in the European Court of Human Rights in Strasbourg.[69] The suit, which was summarily rejected on thesame day, alleged that the Large Hadron Collider posed grave risks for the safety of the 27 member states of theEuropean Union and their citizens.[31] [35] [69]

Late in 2009 a review of the legal situation by Eric Johnson, a lawyer, was published in the Tennessee LawReview.[89] [90] [91] In February 2010 a summary of Johnson's article appeared as an opinion piece in NewScientist.[92]

In February 2010, the German Constitutional Court (Bundesverfassungsgericht) rejected an injunction petition tohalt the LHC's operation as unfounded, without hearing the case, stating that the opponents had failed to produceplausible evidence for their theories.[93]

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[72] Schmidt, Von Wolf (7 September 2008). " Der Prophet des Planetentods (http:/ / www. taz. de/ 1/ zukunft/ wissen/ artikel/ 1/der-prophet-des-planetentods/ )" (in German). Taz.de.

[73] "Comments from Prof. Dr. Hermann Nicolai, Director, Max Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut) Potsdam,Germany on speculations raised by Professor Otto Rössler about the production of black holes at the LHC." (July 2008) (http:/ /environmental-impact. web. cern. ch/ environmental-impact/ Objects/ LHCSafety/ NicolaiComment-en. pdf) (PDF, 16 KiB).

[74] Giulini, Domenico; and Nicolai, Hermann (August 2008). On the arguments of O.E. Rössler (http:/ / environmental-impact. web. cern. ch/environmental-impact/ Objects/ LHCSafety/ NicolaiFurtherComment-en. pdf) (PDF, 96 KiB).

[75] " Couchepin trifft Cern-Kritiker Rössler (http:/ / www. nzz. ch/ nachrichten/ kultur/ literatur_und_kunst/roessler_schwarze_loecher_cern_couchepin_1. 789024. html)" (in German). NZZ Online. 21 July 2008.

[76] " Kein Gespräch zwischen Couchepin und Cern-Kritiker (http:/ / www. nzz. ch/ nachrichten/ wissenschaft/kein_gespraech_zwischen_couchepin_und_cern-kritiker_1. 810880. html)" (in German). NZZ Online. 20 August 2008.

[77] Plaga, Rainer (10 August 2008). On the potential catastrophic risk from metastable quantum-black holes produced at particle colliders(http:/ / arxiv. org/ pdf/ 0808. 1415v3) (PDF). arXiv:0808.1415v3.

[78] Clery, Daniel; & Cho, Adrian (5 September 2008). "Large Hadron Collider: Is the LHC a Doomsday Machine?" Science. Vol. 321. no.5894, p. 1291. doi:10.1126/science.321.5894.1291.

[79] Brean, Joseph (9 September 2008). " Is the end nigh? Science experiment could swallow Earth, critics say (http:/ / www. nationalpost. com/news/ story. html?id=777940& p=1)". National Post.

[80] Giddings, Steven B.; & Mangano, Michelangelo L. (29 August 2008). Comments on claimed risk from metastable black holes (http:/ / arxiv.org/ pdf/ 0808. 4087v1) (PDF). arXiv:0808.4087. CERN-PH-TH/2008-184.

[81] R. Casadio, S. Fabi and B. Harms Possibility of Catastrophic Black Hole Growth in the Warped Brane-World Scenario at the LHC (http:/ /prd. aps. org/ abstract/ PRD/ v80/ i8/ e084036) (PDF).

[82] Overbye, Dennis (29 March 2008). " Asking a Judge to Save the World, and Maybe a Whole Lot More (http:/ / www. nytimes. com/ 2008/03/ 29/ science/ 29collider. html)". The New York Times.

[83] " Sancho v. U.S. Department of Energy et al. (1:2008cv00136) (http:/ / dockets. justia. com/ docket/ court-hidce/ case_no-1:2008cv00136/case_id-78717/ )". Justia Federal District Court Filings & Dockets. 21 March 2008.

[84] " Documentation submitted by plaintiff (http:/ / www. lhcdefense. org/ lhc_legal. php)". LHCDefense.org.[85] Boyle, Alan (16 June 2008). " Doomsday under debate (http:/ / cosmiclog. msnbc. msn. com/ archive/ 2008/ 06/ 16/ 1146317. aspx)".

Cosmic Log. msnbc.com.[86] Overbye, Dennis (27 June 2008). " Government Seeks Dismissal of End-of-World Suit Against Collider (http:/ / www. nytimes. com/ 2008/

06/ 27/ science/ 27collider. html)". The New York Times.[87] Boyle, Alan (26 September 2008). " Doomsday Lawsuit Dismissed (http:/ / cosmiclog. msnbc. msn. com/ archive/ 2008/ 09/ 26/ 1457536.

aspx)". Cosmic Log. msnbc.com.[88] Harris, David (26 August 2010). " LHC lawsuit dismissed by US court (http:/ / www. symmetrymagazine. org/ breaking/ 2010/ 08/ 26/

lhc-lawsuit-dismissed-by-us-court/ )". symmetrybreaking. SLAC/Fermilab.[89] Johnson, Eric E.. "The Black Hole Case". Tennessee Law Review 76: 819–908.[90] Johnson (2009). "The Black Hole Case: The Injunction Against the End of the World". arΧiv:0912.5480v2 [physics.soc-ph].[91] Cartlidge, Edwin (Feb 2, 2010). "Law and the end of the world" (http:/ / physicsworld. com/ cws/ article/ indepth/ 41564). physicsworld.com

(Institute of Physics). . Retrieved 2010-04-01.[92] Johnson, Eric E. (23 February 2010). "CERN on trial: could a lawsuit shut the LHC down?" (http:/ / www. newscientist. com/ article/

mg20527485. 700-cern-on-trial-could-a-lawsuit-shut-the-lhc-down. html?full=true). New Scientist. . Retrieved 2010-04-01.[93] BVerfG, 2 BvR 2502/08 vom 18.2.2010 (http:/ / www. bundesverfassungsgericht. de/ entscheidungen/ rk20100218_2bvr250208. html)

External links• "The safety of the LHC" (http:/ / public. web. cern. ch/ public/ en/ LHC/ Safety-en. html), CERN webpage.• "The LHC is safe" (video) (http:/ / cdsweb. cern. ch/ record/ 1120625?ln=en), talk by John Ellis at CERN, on 14

August 2008.

Micro black hole 99

Micro black holeMBH redirects here. It can also refer to the Hayist Bases Movement, or a unit of power - a thousand BTUsper hour.

Micro black holes are tiny black holes, also called quantum mechanical black holes or mini black holes, forwhich quantum mechanical effects play an important role.[1]

It is possible that such quantum primordial black holes were created in the high-density environment of the earlyUniverse (or big bang), or possibly through subsequent phase transitions. They might be observed by astrophysicistsin the near future, through the particles they are expected to emit by Hawking radiation.Some theories involving additional space dimensions predict that micro black holes could be formed at an energy aslow as the TeV range, which will be available in particle accelerators such as the LHC (Large Hadron Collider).Popular concerns have then been raised over end-of-the-world scenarios (see Safety of particle collisions at the LargeHadron Collider). However, such quantum black holes would instantly evaporate, either totally or leaving only avery weakly interacting residue. Beside the theoretical arguments, we can notice that the cosmic rays bombarding theEarth do not produce any damage, although they reach center of mass energies in the range of hundreds of TeV.

Minimum mass of a black holeIn principle, a black hole can have any mass above the Planck mass. To make a black hole, one must concentratemass or energy sufficiently that the escape velocity from the region in which it is concentrated exceeds the speed oflight. This condition gives the Schwarzschild radius, , where G is Newton's constant and c is thespeed of light, of a black hole of mass M. On the other hand, the Compton wavelength, , where h isPlanck's constant, represents a limit on the minimum size of the region in which a mass M at rest can be localized.For sufficiently small M, the reduced Compton wavelength ( , where ħ is Dirac's constant) exceedshalf the Schwarzschild radius, and no black hole description exists. This smallest mass for a black hole is thusapproximately the Planck mass.Some extensions of present physics posit the existence of extra dimensions of space. In higher-dimensionalspacetime, the strength of gravity increases more rapidly with decreasing distance than in three dimensions. Withcertain special configurations of the extra dimensions, this effect can lower the Planck scale to the TeV range.Examples of such extensions include large extra dimensions, special cases of the Randall-Sundrum model, andString theory configurations like the GKP solutions. In such scenarios, black hole production could possibly be animportant and observable effect at the LHC.[1] [2] [3] [4] [5] It would also be a common natural phenomenon inducedby the cosmic rays.

Stability of a micro black hole

Hawking radiationIn 1974 Stephen Hawking argued that due to quantum effects, black holes "evaporate" by a process now referred toas Hawking Radiation in which elementary particles (photons, electrons, quarks, gluons, etc.) are emitted.[6] Hiscalculations show that the smaller the size of the black hole, the faster the evaporation rate, resulting in a suddenburst of particles as the micro black hole suddenly explodes.Any primordial black hole of sufficiently low mass will Hawking evaporate to near the Planck mass within the lifetime of the Universe. In this process, these small black holes radiate away matter. A rough picture of this is that pairs of virtual particles emerge from the vacuum near the event horizon, with one member of a pair being captured, and the other escaping the vicinity of the black hole. The net result is the black hole loses mass (due to conservation of energy). According to the formulae of black hole thermodynamics, the more the black hole loses mass the hotter it

Micro black hole 100

becomes, and the faster it evaporates, until it approaches the Planck mass. At this stage a black hole would have aHawking temperature of TP / 8π (5.6×1032 K), which means an emitted Hawking particle would have an energycomparable to the mass of the black hole. Thus a thermodynamic description breaks down. Such a mini-black holewould also have an entropy of only 4π nats, approximately the minimum possible value. At this point then, theobject can no longer be described as a classical black hole, and Hawking's calculations also break down.While Hawking radiation is sometimes questioned,[7] Leonard Susskind summarizes an expert perspective in hisrecent book:[8] "Every so often, a physics paper will appear claiming that black holes don't evaporate. Such papersquickly disappear into the infinite junk heap of fringe ideas."

Conjectures for the final stateConjectures for the final fate of the black hole include total evaporation and production of a Planck mass-sized blackhole remnant. It is possible that such Planck-mass black holes, no longer able either to absorb energy gravitationallylike a classical black hole because of the quantised gaps between their allowed energy levels, nor to emit Hawkingparticles for the same reason, may in effect be stable objects. In such case, they would be WIMPs (weaklyinteracting massive particles); this could explain dark matter.

Primordial black holes

Formation in the early UniverseProduction of a black hole requires concentration of mass or energy within the corresponding Schwarzschild radius.It is hypothesized that shortly after the big bang the Universe was dense enough to fit within its own Schwarzschildradius. Even so, at that time the Universe was not able to collapse into a singularity due to its uniform massdistribution and rapid growth. This, however, does not fully exclude the possibility that black holes of various sizesmay have emerged locally. A black hole formed in this way is called a primordial black hole and is the most widelyaccepted theory for the possible creation of micro black holes.

Expected observable effectsPrimordial black holes of initial masses around 1015 grams would be completing their evaporation today; lighterprimordial black holes would have already evaporated.[1] In optimistic circumstances, the Fermi Gamma-ray SpaceTelescope satellite, launched in June 2008, might detect experimental evidence for evaporation of nearby black holesby observing gamma ray bursts.[9] [10] [11] It is unlikely that a collision between a microscopic black hole and anobject such as a star or a planet would be noticeable. This is due to the fact that the small radius and high density ofthe black hole would allow it to pass straight through any object consisting of normal atoms, interacting with onlyfew of its atoms while doing so. It has, however, been suggested that a small black hole (of sufficient mass) passingthrough the Earth would produce a detectable acoustic or seismic signal.[12] [13] [14] [15]

Manmade micro black holes

Can we produce micro black holes?In familiar three-dimensional gravity, the minimum energy of a microscopic black hole is 1019 GeV, which would have to be condensed into a region on the order of the Planck length. This is far beyond the limits of any current technology. It is estimated that to collide two particles to within a distance of a Planck length with currently achievable magnetic field strengths would require a ring accelerator about 1000 light years in diameter to keep the particles on track. Stephen Hawking also said in chapter 6 of his Brief History of Time that physicist John Archibald Wheeler once calculated that a very powerful hydrogen bomb using all the deuterium in all the water on Earth could also generate such a black hole, but Hawking does not provide this calculation or any reference to it to support this

Micro black hole 101

assertion.However, in some scenarios involving extra dimensions of space, the Planck mass can be as low as the TeV range.The Large hadron collider (LHC) has a design energy of 14 TeV for proton-proton collisions and 1150 TeV forPb-Pb collisions. In these circumstances, it was argued in 2001 that black hole production could be an important andobservable effect at the LHC [2] [3] [4] [5] [16] or future higher-energy colliders. Such quantum black holes shoulddecay emitting sprays of particles that could be seen by detectors at these facilities.[2] [3] A recent paper by Choptuikand Pretorius, published on March 17, 2010 in Physical Review Letters presents a computer-generated proof thatmicro black holes must form from two colliding particles with sufficient energy, which might be allowable at theenergies of the LHC if additional dimensions are present other than the customary four (three space, one time).[17]

[18]

Safety argumentsHawking's calculation[6] and more general quantum mechanical arguments predict that micro black holes evaporatealmost instantaneously. Additional safety arguments beyond those based on Hawking radiation were given in thepaper [19] [20] , which showed that in hypothetical scenarios with stable black holes that could damage Earth, suchblack holes would have been produced by cosmic rays and would have already destroyed known astronomicalobjects such as the Earth, Sun, neutron stars, or white dwarfs. Further, microscopic black holes generated from aparticle accelerator are very small in size and are expected to have a high velocity, making it impossible for them toaccrete a dangerously large amount of mass before leaving the earth for good.

Black holes in quantum theories of gravityIt is possible, in some theories of quantum gravity, to calculate the quantum corrections to ordinary, classical blackholes. Contrarily to conventional black holes which are solutions of gravitational field equations of the generaltheory of relativity, quantum gravity black holes incorporate quantum gravity effects in the vicinity of the origin,where classical a curvature singularity occurs. According to the theory employed to model quantum gravity effects,there are different kinds of quantum gravity black holes, namely loop quantum black holes, noncommutative blackholes, asympotically safe black holes. In these approaches black holes are singularity free.

Fiction• In David Brin's novel Earth a manmade micro black hole slips into the core of the earth.• In Dan Simmons's novels Ilium and Olympos, a major landmark is "Paris Crater", the site where a man made

micro black hole's containment field failed, and the black hole sank toward the centre of the earth beforecollapsing (presumably in accordance with the Hawking radiation theory), leaving a volcanic crater in its wake.

• In the short story How We Lost the Moon, A True Story by Frank W. Allen, which is actually written by Paul J.McAuley, a micro black hole is accidentally created on the Moon and gradually consumes it.[21]

• Larry Niven's Hugo Award-winning stories The Hole Man and The Borderland of Sol deal with "quantum blackholes".

• In Martin Caidin's novel Star Bright, an object is created during an implosion-fusion test that has essentially theproperties of a micro black hole, though it is not given that name. The object is eventually destroyed, but theresulting explosion destroys a huge area around it.

• In Steven R. Donaldson's 5 volume Gap series of books he presents singularity grenades as anti-spaceship cosmicweapons that release a micro black hole on impact with a ship.

• In Bungie's award-winning Halo Series, the method of faster-than-light travel for spacecraft is through annondimensional domain known as 'Slipspace', and is made possible by ripping the space-time continuum byhaving slipspace drives artificially generating thousands of micro black holes that quickly evaporate via Hawkingradiation.

Micro black hole 102

• In the Video game Master of Orion II one of the weapons a player can use is a micro black hole generator, whichis used to immobilize and destroy enemy ships.

Notes[1] B.J. Carr and S.B. Giddings, "Quantum black holes," Scientific American 292N5 (2005) 30. (http:/ / www. sciam. com/ article.

cfm?id=quantum-black-holes)[2] Giddings, S. B.; Thomas, S. D. (2002). "High-energy colliders as black hole factories: The End of short distance physics". Phys. Rev. D 65

(5): 056010. doi:10.1103/PhysRevD.65.056010. arXiv:hep-ph/0106219.[3] Dimopoulos, S.; Landsberg, G. L. (2001). "Black Holes at the Large Hadron Collider". Phys. Rev. Lett. 87 (16): 161602.

doi:10.1103/PhysRevLett.87.161602. arXiv:hep-ph/0106295. PMID 11690198.[4] Johnson, George (September 11, 2001). "Physicists Strive to Build A Black Hole" (http:/ / www. nytimes. com/ 2001/ 09/ 11/ science/

physicists-strive-to-build-a-black-hole. html). The New York Times. . Retrieved 2010-05-12.[5] "The case for mini black holes" (http:/ / cerncourier. com/ cws/ article/ cern/ 29199). CERN courier. Nov 2004. .[6] Hawking, S. W. (1975). "Particle Creation by Black Holes". Commun. Math. Phys. 43 (3): 199–220. doi:10.1007/BF02345020.[7] Helfer, A. D. (2003). "Do black holes radiate?". Reports on Progress in Physics 66 (6): 943. doi:10.1088/0034-4885/66/6/202.

arXiv:gr-qc/0304042.[8] Susskind, L. (2008). The Black Hole War: My battle with Stephen Hawking to make the world safe for quantum mechanics. New York: Little,

Brown. ISBN 9780316016407.[9] Barrau, A. (2000). "Primordial black holes as a source of extremely high energy cosmic rays". Astroparticle Physics 12 (4): 269–275.

doi:10.1016/S0927-6505(99)00103-6.[10] McKee, M. (30 May 2006). "Satellite could open door on extra dimension" (http:/ / www. newscientist. com/ article/

dn9240-satellite-could-open-door-on-extra-dimension. html). New Scientist. .[11] "Fermi Gamma Ray Space Telescope: "Mini" black hole detection" (http:/ / fermi. gsfc. nasa. gov/ help/ tech/ minibh. html). .[12] Khriplovich, I. B.; Pomeransky, A. A.; Produit, N.; Ruban, G. Yu. (2008). "Can one detect passage of small black hole through the Earth?".

Physical Review D 77 (6): 064017. doi:10.1103/PhysRevD.77.064017.[13] Khriplovich, I. B.; Pomeransky, A. A.; Produit, N.; Ruban, G. Yu.. "Passage of small black hole through the Earth. Is it detectable?".

Pre-Print. arXiv:0801.4623.[14] Cain, Fraser (20 June 2007). "Are Microscopic Black Holes Buzzing Inside the Earth?" (http:/ / www. universetoday. com/ 2007/ 06/ 20/

are-microscopic-black-holes-buzzing-inside-the-earth). Universe Today. .[15] The Schwarzschild radius of a 1015 grams black hole is ~148 fm (148 ? 10?15 m) (which is much smaller than an atom, but larger than an

atomic nucleus)[16] Schewe, Phillip F.; Stein, Ben; Riordon, James (September 26, 2001). "??". Bulletin of Physics News (American Institute of Physics) 558.[17] Choptuik, Matthew W.; Pretorius, Frans (2010). "Ultrarelativistic Particle Collisions". Phys. Rev. Lett. 104 (11): 111101.

doi:10.1103/PhysRevLett.104.111101. arXiv:0908.1780. PMID 20366461.[18] Peng, G. X.; Wen, X. J.; Chen, Y. D. (2006). "New solutions for the color-flavor locked strangelets". Physics Letters B 633 (2–3): 314–318.

doi:10.1016/j.physletb.2005.11.081. arXiv:hep-ph/0512112.[19] S.B. Giddings and M.L. Mangano, "Astrophysical implications of hypothetical stable TeV-scale black holes," arXiv:0806.3381 (http:/ /

arxiv. org/ abs/ 0806. 3381), Phys. Rev. D78: 035009, 2008 (http:/ / link. aps. org/ doi/ 10. 1103/ PhysRevD. 78. 035009)[20] M.E. Peskin, "The end of the world at the Large Hadron Collider?" Physics 1, 14 (2008) (http:/ / physics. aps. org/ articles/ v1/ 14)[21] http:/ / www. bestsf. net/ reviews/ mcauleylittlemachines. html

References• D. Page, Phys. Rev. D13 (1976) 198 (http:/ / prola. aps. org/ abstract/ PRD/ v13/ i2/ p198_1) : first detailed

studies of the evaporation mechanism• B.J. Carr & S.W. Hawking, Mon. Not. Roy. Astron. Soc 168 (1974) 399 (http:/ / adsabs. harvard. edu/ cgi-bin/

nph-bib_query?bibcode=1974MNRAS. 168. . 399C) : links between primordial black holes and the early universe• A. Barrau et al., Astron. Astrophys. 388 (2002) 676 (http:/ / arxiv. org/ abs/ astro-ph/ 0112486) , Astron.

Astrophys. 398 (2003) 403 (http:/ / arxiv. org/ abs/ astro-ph/ 0207395) , Astrophys. J. 630 (2005) 1015 (http:/ /arxiv. org/ abs/ astro-ph/ 0505436) : experimental searches for primordial black holes thanks to the emittedantimatter

• A. Barrau & G. Boudoul, Review talk given at the International Conference on Theoretical Physics TH2002(http:/ / arxiv. org/ abs/ astro-ph/ 0212225) : cosmology with primordial black holes

Micro black hole 103

• A. Barrau & J. Grain, Phys. Lett. B 584 (2004) 114 (http:/ / arxiv. org/ abs/ hep-ph/ 0311238) : searches for newphysics (quantum gravity) with primordial black holes

• P. Kanti, Int. J. Mod. Phys. A19 (2004) 4899 (http:/ / arxiv. org/ abs/ hep-ph/ 0402168) : evaporating black holesand extra-dimensions

• D. Ida, K.-y. Oda & S.C.Park, (http:/ / arxiv. org/ abs/ hep-th/ 0602188): determination of black hole's life andextra-dimensions

• Sabine Hossenfelder: What Black Holes Can Teach Us, hep-ph/0412265 (http:/ / www. arxiv. org/ abs/ hep-ph/0412265)

• L. Modesto, PhysRevD.70.124009 (http:/ / arxiv. org/ abs/ gr-qc/ 0407097): Disappearance of Black HoleSingularity in Quantum Gravity

• P. Nicolini, A. Smailacic, E. Spallucci, j.physletb.2005.11.004 (http:/ / arxiv. org/ abs/ gr-qc/ 0510112):Noncommutative geometry inspired Schwarzschild black hole

• A. Bonanno, M. Reuter, PhysRevD.73.083005 (http:/ / arxiv. org/ abs/ hep-th/ 0602159): Spacetime Structure ofan Evaporating Black Hole in Quantum Gravity

External links• Astrophysical implications of hypothetical stable TeV-scale black holes (http:/ / arxiv. org/ abs/ 0806. 3381)• A. Barrau & J. Grain, The Case for mini black holes (http:/ / www. cerncourier. com/ main/ article/ 44/ 9/ 22) : a

review of the searches for new physics with micro black holes possibly formed at colliders• Mini Black Holes Might Reveal 5th Dimension (http:/ / www. space. com/ scienceastronomy/

060626_mystery_monday. html) - Space.com• Doomsday Machine Large Hadron Collider? (http:/ / www. ostina. org/ content/ view/ 3547/ 1077/ ) - A scientific

essay about energies, dimensions, black holes, and the associated public attention to CERN, by Norbert Frischauf(also available as Podcast)

Strangelet 104

StrangeletA strangelet is a hypothetical particle consisting of a bound state of roughly equal numbers of up, down, and strangequarks. Its size would be a minimum of a few femtometers across (with the mass of a light nucleus). Once the sizebecomes macroscopic (on the order of meters across), such an object is usually called a quark star or "strange star"rather than a strangelet. An equivalent description is that a strangelet is a small fragment of strange matter. The term"strangelet" originates with E. Farhi and R. Jaffe.[1] Strangelets have been suggested as a dark matter candidate.[2]

Theoretical possibility

Strange matter hypothesisThe known particles with strange quarks are unstable because the strange quark is heavier than the up and downquarks, so strange particles, such as the Lambda particle, which contains an up, down, and strange quark, always losetheir strangeness, by decaying via the weak interaction to lighter particles containing only up and down quarks. Butstates with a larger number of quarks might not suffer from this instability. This is the "strange matter hypothesis" ofBodmer [3] and Witten.[2] According to this hypothesis, when a large enough number of quarks are collectedtogether, the lowest energy state is one which has roughly equal numbers of up, down, and strange quarks, namely astrangelet. This stability would occur because of the Pauli exclusion principle; having three types of quarks, ratherthan two as in normal nuclear matter, allows more quarks to be placed in lower energy levels.

Relationship with nucleiA nucleus is a collection of a large number of up and down quarks, confined into triplets (neutrons and protons).According to the strange matter hypothesis, strangelets are more stable than nuclei, so nuclei are expected to decayinto strangelets. But this process may be extremely slow because there is a large energy barrier to overcome: as theweak interaction starts making a nucleus into a strangelet, the first few strange quarks form strange baryons, such asthe Lambda, which are heavy. Only if many conversions occur almost simultaneously will the number of strangequarks reach the critical proportion required to achieve a lower energy state. This is very unlikely to happen, so evenif the strange matter hypothesis were correct, nuclei would never be seen to decay to strangelets because theirlifetime would be longer than the age of the universe.

SizeThe stability of strangelets depends on their size. This is because of (a) surface tension at the interface between quarkmatter and vacuum (which affects small strangelets more than big ones), and (b) screening of charges, which allowssmall strangelets to be charged, with a neutralizing cloud of electrons/positrons around them, but requires largestrangelets, like any large piece of matter, to be electrically neutral in their interior. The charge screening distancetends to be of the order of a few femtometers, so only the outer few femtometers of a strangelet can carry charge.[4]

The surface tension of strange matter is unknown. If it is smaller than a critical value (a few MeV per squarefemtometer[5] ) then large strangelets are unstable and will tend to fission into smaller strangelets (strange starswould still be stabilized by gravity). If it is larger than the critical value, then strangelets become more stable as theyget bigger.

Strangelet 105

Natural or artificial occurrenceAlthough nuclei do not decay to strangelets, there are other ways to create strangelets, so if the strange matterhypothesis is correct there should be strangelets in the universe. There are at least three ways they might be createdin nature:• Cosmogonically, i.e., in the early universe when the QCD confinement phase transition occurred. It is possible

that strangelets were created along with the neutrons and protons which form ordinary matter.• High energy processes. The universe is full of very high-energy particles (cosmic rays). It is possible that when

these collide with each other or with neutron stars they may provide enough energy to overcome the energybarrier and create strangelets from nuclear matter.

• Cosmic ray impacts. In addition to head-on collisions of cosmic rays, ultra high energy cosmic rays impacting onEarth's atmosphere may create strangelets.

These scenarios offer possibilities for observing strangelets. If there are strangelets flying around the universe, thenoccasionally a strangelet should hit Earth, where it would appear as an exotic type of cosmic ray. If strangelets canbe produced in high energy collisions, then we might make them at heavy-ion colliders.

Accelerator productionAt heavy ion accelerators like RHIC, nuclei are collided at relativistic speeds, creating strange and antistrange quarkswhich could conceivably lead to strangelet production. The experimental signature of a strangelet would be its veryhigh ratio of mass to charge, which would cause its trajectory in a magnetic field to be extremely straight. The STARcollaboration has searched for strangelets produced at the Relativistic Heavy Ion Collider,[6] but none were found.The Large Hadron Collider (LHC) is even less likely to produce strangelets,[7] but searches are planned[8] for theLHC ALICE detector.

Space-based detectionThe Alpha Magnetic Spectrometer (AMS), an instrument which is planned to be mounted on the International SpaceStation, could detect strangelets.[9]

Possible seismic detectionIn May 2002, a group of researchers at Southern Methodist University reported the possibility that strangelets mayhave been responsible for seismic events recorded on October 22 and November 24 in 1993.[10] The authors laterretracted their claim, after finding that the clock of one of the seismic stations had a large error during the relevantperiod.[11]

It has been suggested that the International Monitoring System being set up to verify the Comprehensive NuclearTest Ban Treaty (CTBT) may be useful as a sort of "strangelet observatory" using the entire Earth as its detector. TheIMS will be designed to detect anomalous seismic disturbances down to 1 kiloton of TNT's equivalent energy releaseor less, and could be able to track strangelets passing through Earth in real time if properly exploited.

DangersIf the strange matter hypothesis is correct and a strangelet comes in contact with a lump of ordinary matter such asEarth, it could convert the ordinary matter to strange matter.[12] [13] This "ice-nine"-like disaster scenario is asfollows: one strangelet hits a nucleus, catalyzing its immediate conversion to strange matter. This liberates energy,producing a larger, more stable strangelet, which in turn hits another nucleus, catalyzing its conversion to strangematter. In the end, all the nuclei of all the atoms of Earth are converted, and Earth is reduced to a hot, large lump ofstrange matter.

Strangelet 106

This is not a concern for strangelets in cosmic rays because they are produced far from Earth and have had time todecay to their ground state, which is predicted by most models to be positively charged, so they are electrostaticallyrepelled by nuclei, and would rarely merge with them.[14] [15] But high-energy collisions could produce negativelycharged strangelet states which live long enough to interact with the nuclei of ordinary matter.[16]

The danger of catalyzed conversion by strangelets produced in heavy-ion colliders has received some mediaattention,[17] [18] and concerns of this type were raised[12] [19] at the commencement of the Relativistic Heavy IonCollider (RHIC) experiment at Brookhaven, which could potentially have created strangelets. A detailed analysis[13]

concluded that the RHIC collisions were comparable to ones which naturally occur as cosmic rays traverse the solarsystem, so we would already have seen such a disaster if it were possible. RHIC has been operating since 2000without incident. Similar concerns have been raised about the operation of the Large Hadron Collider (LHC) atCERN[20] but such fears are dismissed as far-fetched by scientists.[20] [21] [22]

In the case of a neutron star, the conversion scenario seems much more plausible. A neutron star is in a sense a giantnucleus (20 km across), held together by gravity, but it is electrically neutral and so does not electrostatically repelstrangelets. If a strangelet hit a neutron star, it could convert a small region of it, and that region would grow toconsume the entire star, creating a quark star.[23]

All the issues discussed above relating to the conversion of ordinary matter to strange matter only arise if the strangematter hypothesis is true, and its surface tension is larger than the aforementioned critical value.

Debate about the strange matter hypothesisThe strange matter hypothesis remains unproven. No direct search for strangelets in cosmic rays or particleaccelerators has seen a strangelet (see references in earlier sections). If any of the objects we call neutron stars couldbe shown to have a surface made of strange matter, this would indicate that strange matter is stable at zero pressure,which would vindicate the strange matter hypothesis. But there is no strong evidence for strange matter surfaces onneutron stars (see below).Another argument against the hypothesis is that if it were true, all neutron stars should be made of strange matter,and otherwise none should be.[24] Even if there were only a few strange stars initially, violent events such ascollisions would soon create many strangelets flying around the universe. Because one strangelet will convert aneutron star to strange matter, by now all neutron stars would have been converted. This argument is still debated,[25]

[26] [27] [28] but if it is correct then showing that one neutron star has a conventional nuclear matter crust woulddisprove the strange matter hypothesis.Because of its importance for the strange matter hypothesis, there is an ongoing effort to determine whether thesurfaces of neutron stars are made of strange matter or nuclear matter. The evidence currently favors nuclear matter.This comes from the phenomenology of X-ray bursts, which is well-explained in terms of a nuclear matter crust,[29]

and from measurement of seismic vibrations in magnetars.[30]

In fictionAn episode of Odyssey 5 featured an attempt to destroy the planet by intentionally creating negatively chargedstrangelets in a particle accelerator.[31]

The BBC docufiction End Day features a scenario where a particle accelerator in New York City explodes, creatinga strangelet and starting a catastrophic chain reaction which destroys Earth.The story "A Matter most Strange" in the collection Indistinguishable from Magic by Robert L. Forward deals withthe making of strangelet in a particle accelerator.Impact (novel), published in 2010 and written by Douglas Preston, deals with an alien machine that createsstrangelets. The machine's strangelets impact the Earth and Moon and pass through.

Strangelet 107

"Killer Strangelets" by C.T. Furlong is a children's novel about a group of kids trying to stop an evil scientist fromdestroying the planet using strangelets.The latest installment in the Mayan trilogy by Steve Alten, called "Phobos: Mayan Fear" a Strangelet, probablyoriginated from the GHC, is capable of opening Time/Space distortions and completely destroys the Earth at leastonce.

References[1] E. Farhi and R. Jaffe, "Strange Matter", Phys. Rev. D30, 2379 (1984) (http:/ / prola. aps. org/ abstract/ PRD/ v30/ i11/ p2379_1)[2] E. Witten, "Cosmic Separation Of Phases" Phys. Rev. D30, 272 (1984) (http:/ / prola. aps. org/ abstract/ PRD/ v30/ i2/ p272_1)[3] A. Bodmer "Collapsed Nuclei" Phys. Rev. D4, 1601 (1971) (http:/ / prola. aps. org/ abstract/ PRD/ v4/ i6/ p1601_1)[4] H. Heiselberg, "Screening in quark droplets", Phys. Rev. D48, 1418 (1993) (http:/ / prola. aps. org/ abstract/ PRD/ v48/ i3/ p1418_1)[5] M. Alford, K. Rajagopal, S. Reddy, A. Steiner, "The Stability of Strange Star Crusts and Strangelets", Phys. Rev. D73 114016 (2006)

arXiv:hep-ph/0604134 (http:/ / arxiv. org/ abs/ hep-ph/ 0604134)[6] STAR Collaboration, "Strangelet search at RHIC", arXiv:nucl-ex/0511047 (http:/ / www. arxiv. org/ abs/ nucl-ex/ 0511047)[7] Ellis J, Giudice G, Mangano ML, Tkachev I, Wiedemann U (LHC Safety Assessment Group) (5 September 2008). " Review of the Safety of

LHC Collisions (http:/ / www. iop. org/ EJ/ article/ 0954-3899/ 35/ 11/ 115004/ g8_11_115004.pdf?request-id=1973667e-34da-47a4-b75a-08624558a81b)" (PDF, 586 KiB). ''Journal of Physics G: Nuclear and Particle Physics. 35,115004 (18pp). doi:10.1088/0954-3899/35/11/115004. arXiv:0806.3414. CERN record (http:/ / cdsweb. cern. ch/ record/ 1111112?ln=fr).

[8] A. Angelis et al., "Model of Centauro and strangelet production in heavy ion collisions", Phys. Atom. Nucl. 67:396-405 (2004)arXiv:nucl-th/0301003 (http:/ / arxiv. org/ abs/ nucl-th/ 0301003)

[9] J. Sandweiss, "Overview of strangelet searches and Alpha Magnetic Spectrometer: When will we stop searching?" J. Phys. G30:S51-S59(2004) (http:/ / www. iop. org/ EJ/ abstract/ 0954-3899/ 30/ 1/ 004)

[10] D. Anderson et al., "Two seismic events with the properties for the passage of strange quark matter through the earth"arXiv:astro-ph/0205089 (http:/ / www. arxiv. org/ abs/ astro-ph/ 0205089)

[11] E.T. Herrin et al., "Seismic Search for Strange Quark Nuggets" (http:/ / arxiv. org/ abs/ astro-ph/ 0505584)[12] A. Dar, A. De Rujula, U. Heinz, "Will relativistic heavy ion colliders destroy our planet?", Phys. Lett. B470:142-148 (1999)

arXiv:hep-ph/9910471 (http:/ / www. arxiv. org/ abs/ hep-ph/ 9910471)[13] W. Busza, R. Jaffe, J. Sandweiss, F. Wilczek, "Review of speculative 'disaster scenarios' at RHIC", Rev. Mod. Phys.72:1125-1140 (2000)

arXiv:hep-ph/9910333 (http:/ / www. arxiv. org/ abs/ hep-ph/ 9910333)[14] J. Madsen, "Intermediate mass strangelets are positively charged", Phys. Rev. Lett. 85 (2000) 4687-4690 (2000) arXiv:hep-ph/0008217

(http:/ / www. arxiv. org/ abs/ hep-ph/ 0008217)[15] J. Madsen "Strangelets in Cosmic Rays", for Proceedings of 11th Marcel Grossmann Meeting, Germany, Jul 2006, arXiv:astro-ph/0612784

(http:/ / www. arxiv. org/ abs/ astro-ph/ 0612784)[16] J. Schaffner-Bielich, C. Greiner, A. Diener, H. Stoecker, "Detectability of strange matter in heavy ion experiments", Phys. Rev.

C55:3038-3046 (1997), arXiv:nucl-th/9611052 (http:/ / arxiv. org/ abs/ nucl-th/ 9611052)[17] New Scientist, 28 August 1999: "A Black Hole Ate My Planet" (http:/ / www. kressworks. com/ Science/ A_black_hole_ate_my_planet.

htm)[18] Horizon: End Days, an episode of the BBC television series Horizon[19] W. Wagner, "Black holes at Brookhaven?" and reply by F. Wilzcek, Letters to the Editor, Scientific American July 1999[20] Dennis Overbye, Asking a Judge to Save the World, and Maybe a Whole Lot More, NY Times, 29 March 2008 (http:/ / www. nytimes. com/

2008/ 03/ 29/ science/ 29collider. html?ref=us)[21] "Safety at the LHC" (http:/ / public. web. cern. ch/ Public/ en/ LHC/ Safety-en. html). .[22] J. Blaizot et al., "Study of Potentially Dangerous Events During Heavy-Ion Collisions at the LHC", CERN library record (http:/ / cdsweb.

cern. ch/ search?sysno=002372601cer) CERN Yellow Reports Server (PDF) (http:/ / doc. cern. ch/ yellowrep/ 2003/ 2003-001/ p1. pdf)[23] Astrophys. Journal 310: 261. 1986. "Strange stars" (http:/ / adsabs. harvard. edu/ full/ 1986ApJ. . . 310. . 261A).[24] J. Friedman and R. Caldwell, "Evidence against a strange ground state for baryons", Phys. Lett. B264, 143-148 (1991)[25] J. Madsen, "Strangelets as cosmic rays beyond the GZK-cutoff", Phys. Rev. Lett. 90:121102 (2003) arXiv:stro-ph/0211597 (http:/ / www.

arxiv. org/ abs/ astro-ph/ 0211597)[26] S. Balberg, "Comment on 'strangelets as cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff'", Phys. Rev. Lett. 92:119001 (2004),

arXiv:astro-ph/0403503 (http:/ / www. arxiv. org/ abs/ astro-ph/ 0403503)[27] J. Madsen, "Reply to Comment on Strangelets as Cosmic Rays beyond the Greisen-Zatsepin-Kuzmin Cutoff", Phys. Rev.Lett. 92:119002

(2004), arXiv:astro-ph/0403515 (http:/ / www. arxiv. org/ abs/ astro-ph/ 0403515)[28] J. Madsen, "Strangelet propagation and cosmic ray flux",Phys. Rev. D71, 014026 (2005) arXiv:astro-ph/0411538 (http:/ / www. arxiv. org/

abs/ astro-ph/ 0411538)[29] A. Heger, A. Cumming, D. Galloway, S. Woosley, "Models of Type I X-ray Bursts from GS 1826-24: A Probe of rp-Process Hydrogen

Burning", arXiv:0711.1195 (http:/ / arxiv. org/ abs/ 0711. 1195)

Strangelet 108

[30] A. Watts and S. Reddy, "Magnetar oscillations pose challenges for strange stars", MNRAS, 379, L63 (2007) arXiv:astro-ph/0609364 (http:// arxiv. org/ abs/ astro-ph/ 0609364)

[31] Odyssey 5: Trouble with Harry (http:/ / www. imdb. com/ title/ tt0664394/ ), an episode of the Canadian science fiction television seriesOdyssey 5 by Manny Coto (2002)

Further reading• Holden, Joshua (May 17, 1998). "The Story of Strangelets" (http:/ / www. physics. rutgers. edu/ ~jholden/

strange/ strange. html). Rutgers. Retrieved 2010-04-01.• Fridolin Weber (2004). "Strange Quark Matter and Compact Stars". arΧiv:astro-ph/0407155 [astro-ph].• Jes Madsen (1998). "Physics and Astrophysics of Strange Quark Matter". arΧiv:astro-ph/9809032 [astro-ph].

109

Future

Super Large Hadron Collider

Intersecting Storage Rings CERN, 1971–1984

Super Proton Synchrotron CERN, 1981–1984

ISABELLE BNL, cancelled in 1983

Tevatron Fermilab, 1987–present

Relativistic Heavy Ion Collider BNL, 2000–present

Superconducting Super Collider Cancelled in 1993

Large Hadron Collider CERN, 2009–present

Super Large Hadron Collider Proposed, CERN, 2019–

Very Large Hadron Collider Theoretical

The Super Large Hadron Collider (SLHC) is a proposed upgrade to the Large Hadron Collider to be made afteraround ten years of operation. The upgrade aims at increasing the luminosity of the machine by a factor of 10, up to1035cm−2s−1, providing a better chance to see rare processes and improving statistically marginal measurements.Many different paths exist for upgrading the collider. A collection of different designs of the high luminosityinteraction regions is being maintained by the European Organization for Nuclear Research (CERN).[1] A workshopwas held in 2006 to establish which are the most promising options.[2] A comprehensive press article on thisworkshop can be found at the CERN Courier [3]. A summary of the possible machine parameters can be found atMachine parameters collection [4].Increasing LHC luminosity involves reduction of beam size at the collision point and either reduction of bunchlength and spacing, or significant increase in bunch length and population. The maximum integrated luminosityincrease of the existing options is about a factor of 4 higher than the LHC ultimate performance, unfortunately farbelow the LHC upgrade project's initial ambition of a factor of 10. However, at the latest LUMI'06 workshop,[2]

several suggestions were proposed that would boost the LHC peak luminosity by a factor of 10 beyond nominaltowards 1035 cm−2s−1.The resultant higher event rate poses important challenges for the particle detectors located in the collision areas.[5]

Injector upgradeAs part of the Phase 2 Super LHC, significant changes would be made to the proton injector.Superconducting Proton Linac (SPL): Accelerating protons with superconducting radio frequency cavities to anenergy of 5GeV.Proton Synchrotron 2 (PS2): Accelerating the beam from 5GeV at injection to 50GeV at extraction.Super Proton Synchroton (SPS) Upgraded: The present SPS would be substantially upgraded to handle in increasedbeam intensity from PS2.

Super Large Hadron Collider 110

References[1] IR optics collection (http:/ / care-hhh. web. cern. ch/ care-hhh/ SuperLHC_IRoptics/ IRoptics. html)[2] LUMI 06 workshop (http:/ / care-hhh. web. cern. ch/ CARE-HHH/ LUMI-06/ default. html)[3] http:/ / cerncourier. com/ cws/ article/ cern/ 29838[4] http:/ / care-hhh. web. cern. ch/ CARE-HHH/ LUMI-06/ lhcupgradeparameters. htm[5] ATLAS upgrade web page (http:/ / atlas. web. cern. ch/ Atlas/ GROUPS/ UPGRADES/ )

Very Large Hadron Collider 111

Very Large Hadron Collider

Intersecting Storage Rings CERN, 1971–1984

Super Proton Synchrotron CERN, 1981–1984

ISABELLE BNL, cancelled in 1983

Tevatron Fermilab, 1987–present

Relativistic Heavy Ion Collider BNL, 2000–present

Superconducting Super Collider Cancelled in 1993

Large Hadron Collider CERN, 2009–present

Super Large Hadron Collider Proposed, CERN, 2019–

Very Large Hadron Collider Theoretical

The Very Large Hadron Collider (VLHC) is a name for a hypothetical future hadron collider with performancesignificantly beyond the Large Hadron Collider.[1]

There is no planned location or schedule for the VLHC; the name is used only to discuss the technological feasibilityof such a collider and ways that it might be designed.Given that such a performance increase necessitates a correspondingly large increase in size, cost, and powerrequirements, a significant amount of international collaboration over a period of decades would be required toconstruct such a collider.

References[1] Glanz, James (2001-07-10). "Physicists Unite, Sort of, on Next Collider" (http:/ / www. nytimes. com/ 2001/ 07/ 10/ science/

physicists-unite-sort-of-on-next-collider. html). The New York Times. . Retrieved 2009-06-27.

External links• vlhc.org (http:/ / vlhc. org/ ), a Fermilab webpage on VLHC research and development• VLHC Design Materials (http:/ / tdserver1. fnal. gov/ tddoc/ DesignStudyReport/ )

Article Sources and Contributors 112

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Voortle, Vsmith, Wafulz, Wangi, WannabeAmatureHistorian, WaysToEscape, Wbrice83186, Wdfarmer, WebScientist, WeirdEars, WereSpielChequers, WikiLaurent, Wikidsoup,Wildthing61476, William Avery, Willking1979, Wiseoldbum, Wk muriithi, Wleizero, Wnt, Wolf1728, Wond3rbread1991, Wonderflash1111, WookieInHeat, Wotnow, Wtmitchell, Wwheaton,XJamRastafire, XP1, Xasdas, Xertoz, YUL89YYZ, Yamamoto Ichiro, Yellowdesk, Yhkhoo, Ylai, Yuefairchild, ZZ9pluralZalpha, Zaak, Zargulon, Zimbabweed, Zomglolwtfzor, Zonk43, Zsinj,Ztbbq, Ztobor, Zucchinidreams, Zykure, Zythe, 1482 anonymous edits

List of LHC experiments  Source: http://en.wikipedia.org/w/index.php?oldid=393844681  Contributors: Auntof6, Headbomb, Ironholds, Rursus, Tetrflare, Xezbeth, 6 anonymous edits

ALICE  Source: http://en.wikipedia.org/w/index.php?oldid=393571510  Contributors: Andrius.v, Caiyu, Connor Behan, Dsupriya, Econ oh my, Edgar181, Erik J, Erwinrossen, Franznavach,Harp, Headbomb, Javachan, Khukri, Kyurkewicz, Laurascudder, LeoNomis, Madhero88, MagdaGa, Meno25, Merrybrit, Mnmngb, One, RafaAzevedo, Rich Farmbrough, SCZenz, Seneka,Sensenmann, Tainels, Tide rolls, Xinebbsa, Мыша, 57 anonymous edits

ATLAS  Source: http://en.wikipedia.org/w/index.php?oldid=397684841  Contributors: 84user, AB, AcademyAD, Akamad, Amapelli, AndrewWatt, Andrius.v, Apis O-tang, Bcrowell,Bobblewik, Bovineone, Bridgeplayer, Bunchofgrapes, Bzzybee13, Charles Matthews, Ciphers, Col. Hauler, Cowman109, Curps, Cyberia23, Cynicism addict, Davdde, Djinn65,DragonflySixtyseven, Ehn, Erkcan, Flying fish, Francphy5, Francs2000, Freakofnurture, Frencheigh, GangofOne, Gene Nygaard, Gregb, Gurch, Harp, Harryboyles, Headbomb, Herr apa, IdaShaw, Jag123, Jmnbatista, Joopercoopers, Juhanson, Khukri, Kozuch, Kyurkewicz, Laurascudder, LeoNomis, Linas, Loodog, Lumidek, Lupin, MagdaGa, Mako098765, Mallorn, Mandavi,Manfalk, Martijn Hoekstra, Master z0b, Matt Crypto, Maxkramer, Mets501, Mithridates, Mjaekel, Neparis, Nick Number, O. Harris, Orion11M87, Pediadeep, PeterMcCready, Plasticup, Rama,Rich Farmbrough, Rjwilmsi, Rob.derosa, SCZenz, SandyGeorgia, Sdedeo, Sfdan, Sheliak, SimonP, SinWin, Spellmaster, Splash, Ssayler, Suruena, Susvolans, The wub, Tm1729, Tony1,Tushar.bhatnagar, V9, Vald, WISo, Wayward, Wiki alf, Woodrowr, Z6, Zondor, 123 anonymous edits

CMS  Source: http://en.wikipedia.org/w/index.php?oldid=404833661  Contributors: Angelastic, Beno1000, Besselfunctions, Bkell, Bornerdogge, Chandrasonic, Chronitis, Cougarsoul, Dirc,Erkcan, Everyme, Falcorian, GeeJo, Gene Nygaard, Harp, Headbomb, Herbee, Icalanise, Isnow, JabberWok, Jimbrooke, Jll, Jz 007, Khukri, Kyurkewicz, Laurascudder, LeoNomis, LokiClock,LorenzoB, MagdaGa, MartinGrunewald, Michael Hardy, Mnmngb, Murielvd, Netrapt, Nevit, Nonnormalizable, Ojs, Pizza1512, Qking, Rama, Reality3chick, Rich Farmbrough, Rjwilmsi,SchmittM, Sheliak, Slashme, Slathering, Spellage, Suruena, Techieb0y, Tiki2099, Tkolberg, Topperfalkon, TriTertButoxy, WISo, Zarniwoot, Δζ, 84 anonymous edits

LHCb  Source: http://en.wikipedia.org/w/index.php?oldid=405758384  Contributors: A1056207, AndyBuckley, Barry m, Conscious, DJIndica, Davdde, GraemeL, Harp, Headbomb, KeenanPepper, Khukri, Kyurkewicz, Larosch, Laurascudder, LeoNomis, Linas, Mark Williamson, Minimac, Nick, Oswald le fort, Pip2andahalf, Pkoppenb, Remuel, Rich Farmbrough, Ryan Roos,SCZenz, Sheliak, Spike Wilbury, Steve Quinn, Themisb, Turnstep, WISo, 28 anonymous edits

LHCf  Source: http://en.wikipedia.org/w/index.php?oldid=403789302  Contributors: Alby, Alessia2703, Alynna Kasmira, Bobo192, CaptinJohn, Davdde, Erkcan, Headbomb, Javachan, Khukri,Kyurkewicz, Laurascudder, LeoNomis, Orion11M87, Puzl bustr, Rich Farmbrough, Sheliak, Welsh, 12 anonymous edits

FP420  Source: http://en.wikipedia.org/w/index.php?oldid=353524901  Contributors: Headbomb, Jakkinx, Rettetast, Slyatslys, Thomas Blomberg

TOTEM  Source: http://en.wikipedia.org/w/index.php?oldid=403795962  Contributors: 7segment, Adrian 1111, Conscious, Francoroldan, Gortu, Harp, Headbomb, Javachan, Jcw69, Kaspar.jan,Khukri, Kyurkewicz, Laurascudder, LeoNomis, Philopp, Rapsar, Rich Farmbrough, Sheliak, 13 anonymous edits

Beetle ASIC  Source: http://en.wikipedia.org/w/index.php?oldid=405751199  Contributors: Amakuru, Cburnett, Gary King, Headbomb, JonHarder, Larosch, RJFJR, Toffile, 2 anonymous edits

LHC Computing Grid  Source: http://en.wikipedia.org/w/index.php?oldid=397412246  Contributors: Beland, Bender235, BillinSanDiego, Bobbias, Cgingold, Chrishmt0423, Cobaltbluetony,Edward, Egil, Eleveneleven, Ethyr, Fifieldt, GregorB, Headbomb, IG-64, JMacalinao, Jbond00747, JukoFF, Kolbasz, Legosock, Lightmouse, Mattgirling, Pakaraki, Randysnow, Sim@simpol.net,Superm401, Twigboy, Walkingstick3, 33 anonymous edits

LHC@home  Source: http://en.wikipedia.org/w/index.php?oldid=395593943  Contributors: .snoopy., 100110100, Bender235, Beno1000, Beyazid, Bovineone, Bruce89, Cgingold, Creidieki,Dirk P Broer, Echoray, Erkcan, Eyreland, FayssalF, Gamer007, GeneralBelly, Giftlite, Headbomb, Hellcat fighter, Hex87, Ilyanep, Jjhat1, Justice Marshall, Kinhull, Laurascudder, LeoNomis,Lzur, Maurice Carbonaro, Minghong, Mr. Billion, Noderaser, Nucleusboy, PrimeHunter, Professorolous, Pstanton, Rich Farmbrough, RoyBoy, SCZenz, The CISer, Valodzka, Visée, Wdfarmer,Wikiacc, Wwoods, Ysangkok, ZeroOne, 13 anonymous edits

Proton Synchrotron Booster  Source: http://en.wikipedia.org/w/index.php?oldid=353617189  Contributors: Andrius.v, Buddy431, Eshmo, Headbomb, Khukri, Laurascudder, Rtomas, Sheliak, 4anonymous edits

VELO  Source: http://en.wikipedia.org/w/index.php?oldid=357996895  Contributors: Bhadani, Headbomb, Larosch, Madcoverboy, Malcolma, Nateji77, Passportguy, Themisb

Standard Model  Source: http://en.wikipedia.org/w/index.php?oldid=407509992  Contributors: A. di M., APH, Addshore, Afteread, Agasicles, Agasides, Aknochel, Alan Liefting, Alansohn,Alinor, Aliotra, Alison, AmarChandra, Andre Engels, AnonMoos, Aoosten, Arivero, AugPi, Awren, AxelBoldt, Axl, Bakken, Bambaiah, Bamkin, Barak Sh, Bassbonerocks, BenRG, Benbest,Bender235, Beta Orionis, Bevo, Bodhitha, Bookalign, Bovineone, Brews ohare, Brim, Brockert, Bryan Derksen, Bubba73, Bytbox, C0nanPayne, CYD, Caco de vidro, CattleGirl, Chris thespeller, ChristopherWillis, Complexica, Craig Bolon, Crazz bug 5, Crum375, D-Notice, DWHalliday, Daniel.Cardenas, DannyWilde, Dauto, Dave1g, David Barnard, David Schaich, Davidspector, Dbenbenn, Dbraize, Deepmath, DerNeedle, Derek Ross, Dextrose, Dfan, Diagramma Della Verita, Djr32, Dmmaus, Dratman, Drhex, Drrngrvy, Drxenocide, Dstudent, Dv82matt,Dysepsion, Edsegal, Eeekster, Egg, Ekjon Lok, El C, Elsweyn, Epbr123, Ernsts, Escalona, FT2, Faethon, Faethon34, Faethon36, Fences and windows, Fogger, FrankTobia, Gary King, Gatortpk,Geremia, Giftlite, Glenn, Gnixon, Goop Goop, Goudzovski, Gparker, Gscshoyru, Guarracino, Guy Harris, H2g2bob, HEL, Hal peridol, Haoherb428, Harp, Harrigan, Headbomb, Herbee,Hexane2000, Hirak 99, HorsePunchKid, HungarianBarbarian, Icairns, Icalanise, Iomesus, Isis, Itinerant1, J Milburn, J.delanoy, JLaTondre, JabberWok, Jacksonwalters, Jagged 85, JamesAM,JarahE, JeffBobFrank, Jeffq, Jeodesic, Jessemv, Jgwacker, Jim E. Black, Jmnbatista, Joshmt, Jrf, Jrtayloriv, Jrw@pobox.com, JulesH, Julesd, Kacser, Kate, KathrynLybarger, Kenmint, Kocio,Laurascudder, LeYaYa, Len Raymond, Leszek Jańczuk, Likebox, LilHelpa, Linas, Lomn, Looxix, Lottamiata, MJ94, Macumba, Maldmac, Melchoir, Metacomet, Michael C Price, MichaelHardy, Michaelbusch, Mindmatrix, Mjamja, Monedula, Moose-32, Mosaffa, MovGP0, Mpatel, Mxn, Naraht, Nozzer42, Ohwilleke, Ordovico, Orion11M87, Orionus, Patrick, Pharotic, Phr, Phys,Physicist brazuca, Physics therapist, Populus, QFT, QMarion II, Qwertyca, R.e.b., RG2, Ram-Man, Rama, Raven in Orbit, Rbj, Reddi, Rjwilmsi, Rmrfstar, Roadrunner, Robdunst, Roscoe x,SCZenz, Schucker, SebastianHelm, Securiger, Setanta747 (locked), Setreset, SheepNotGoats, Sheliak, Silly rabbit, Sligocki, Soarhead77, Sonjaaa, Stannered, Steve Quinn, Stevertigo, Stillnotelf,Stormymountain, Superm401, Superwj5, Swamy g, TPickup, Tanner Swett, Tarcieri, Tariqhada, Template namespace initialisation script, TenOfAllTrades, Tetracube, Texture, That Guy, FromThat Show!, The Anome, The Transliterator, Thunderboltz, Tom Lougheed, TriTertButoxy, Truthnlove, Twas Now, UnitedStatesian, UniversumExNihilo, Van helsing, Verdy p, Vessels42,Voorlandt, VoxMoose, WJBscribe, Waggers, Wilhelm-physiker, Wing gundam, Wwheaton, Xerxes314, Xezbeth, YellowMonkey, Yevgeny Kats, Youandme, 302 anonymous edits

Particle physics  Source: http://en.wikipedia.org/w/index.php?oldid=403139326  Contributors: 128.12.93.xxx, 142.58.249.xxx, 64.26.98.xxx, APH, Agerom, Ahoerstemeier, Aknochel,Alansohn, Allstarecho, Almostcrime, AndreasJS, Archer7, Arekku, Ark, Aroodman, Arthena, Atlant, Austin Maxwell, Awmarcz, AxelBoldt, Bambaiah, Bamkin, Barbara Shack, Battlemage,Bdesham, Bennylin, Bevo, Bggoldie, Bm gub, BobertWABC, Bobo192, Bodhitha, Boing! said Zebedee, Boud, Brandonlovescrashincastles, Brews ohare, BurtPeck, CRGreathouse, CRKingston,CWii, CYD, Calmypal, Caltas, CambridgeBayWeather, Can't sleep, clown will eat me, Celithemis, Ch2pgj, Chenyu, Cjc38, CloudNineAC, Complex (de), Comrade42, Conversion script,Csgwon, Cybercobra, DHN, DV8 2XL, Dauto, Deglr6328, Dev 176, Diligent Terrier, Discospinster, Djegan, Docu, Dominick, Donarreiskoffer, Donzzz77, Edward Z. Yang, El C, El Snubbe,Ellywa, Elodzinski, Eloquence, EmanCunha, Emijrp, Eog1916, Erwinrossen, FT2, Falcon8765, Falconkhe, Fieldday-sunday, Fruge, Gaius Cornelius, Gareth Owen, Gary King, Gbrandt,GeorgeLouis, Ghalhud, Giftlite, Glenn, Gnixon, Gnomon Kelemen, Goodnightmush, Goudzovski, Graham87, Hdeasy, Head, Headbomb, Hectorthebat, Henry W. Schmitt, Hfastedge,Howdychicken, Howie Goodell, Ilmari Karonen, Immunize, Inwind, Iridescent, Isnow, Ixfd64, J.delanoy, JRR Trollkien, JaGa, Jagged 85, Jameskeates, Jamesontai, JamieS93, Jgwacker,JimVC3, Jimbill4321, Joe N, Joe iNsecure, Jomoal99, JonasRH, Joshmt, Joshua P. Schroeder, Jpowell, Jung dalglish, Jxzj, Kakofonous, Karol Langner, Kbrose, Kenneth M Burke, Kocio,Korath, Kozuch, Kuru, Kurzon, LX, Langsytank, Larry Sanger, Laussy, Le sacre, Lee Daniel Crocker, Lightdarkness, Lightmouse, Ling.Nut, Looxix, Lor772, Lseixas, Lumidek, Lupin, MER-C,MK8, Mako098765, Marcus Qwertyus, Master Jay, Matt Crypto, Matt Gies, Matthew Woodcraft, Mattmartin, Maurreen, Mav, Mayumashu, Mcneile, Md7t, Melchoir, Mermaid from the BalticSea, Metrictensor, Mets501, Michael Hardy, MichaelMaggs, Micraboy, Mignon, Mike2vil, MonoAV, MoogleEXE, Mouse7525, Mpatel, Mullactalk, Munkay, Mxn, NellieBly, News0969,Novacatz, NuclearWinner, Ohwilleke, Oldnoah, Olexandr Kravchuk, OpenToppedBus, Orion11M87, Orpheus, Oxymoron83, Palfrey, Pandacomics, Party, Patrick, Pcd72, Pchapman47879,Penarestel, Pet3r, PhySusie, Phys, Physics, Physicsdavid, Physis, Planlips, Plastadity, Poopfacer, PranksterTurtle, QFT, RE, Ragesoss, Raphtee, Raul654, Ravi12346, Redvers, Res2216firestar,Rholton, Rich Farmbrough, Rje, Rl, Roadrunner, Rorro, Ryan Postlethwaite, SCZenz, Saeed.Veradi, SaltyBoatr, Sanders muc, Savidan, Scottfisher, Selkem, Shawn in Montreal, Silly rabbit,SimonMayer, SimonP, Sjakkalle, Smarcus, Snigbrook, Sodium, Someguy1221, Srleffler, Stephenb, Steve Quinn, SwordSmurf, TallMagic, Techraj, The Epopt, Tpbradbury, Trecool12, Trelvis,Truthnlove, Tycho, UncleDouggie, UninvitedCompany, Urvabara, Van helsing, VictorFlaushenstein, Vishnava, Voidxor, Voyajer, Wavelength, Who, Witguiota, XJamRastafire, Ylai,Zanzerjewel, Ъыь, 374 anonymous edits

Superpartner  Source: http://en.wikipedia.org/w/index.php?oldid=404298929  Contributors: Alai, Antixt, Barak Sh, Bobathon71, Carlog3, Conscious, Donarreiskoffer, Drrngrvy, Duncan.france,Flloater, Giftlite, Headbomb, Jgwacker, Kocio, LovroZitnik, Madacs, Maliz, Mpatel, Phys, R.e.b., Reedy, Roadrunner, SCZenz, SimonP, SkyLined, 5 anonymous edits

Supersymmetry  Source: http://en.wikipedia.org/w/index.php?oldid=405975329  Contributors: Acjohnson55, Aknochel, Ancheta Wis, Andre Engels, Anville, Arivero, Barak Sh, BenRG, Blaxthos, Bodera, Bryan Derksen, C9, CES1596, Cadmasteradam, Can't sleep, clown will eat me, Cgingold, Chaos, Charles Matthews, Charleswestbrook, Chessmaster7m, Cless Alvein,

Article Sources and Contributors 114

Closedmouth, Complexica, Crum375, Cuboidal, DO'Neil, Dan Gluck, Ddimensões, Deglr6328, Djloststylez, Drrngrvy, Duk, Eddie Nixon, El C, Epolk, F Notebook, Ferkelparade, Francescog,Fropuff, Gagoga ju, Gary King, Giftlite, Gil987, Girl Scout cookie, Gparker, Gsard, Gus Polly, HaloStereo1, Headbomb, IMSoP, J.christianson, JarahE, Jcpilman, Jeandré du Toit, Jgwacker,Jordan14, Josiah Rowe, Jpod2, Kawakameha, Kborland, Kevin Hickerson, Killing Vector, Koeplinger, Kostisl, Kurochka, Lambiam, LiDaobing, LostLeviathan, Lumidek, MFH, Maarten vanVliet, Maliz, Maurice Carbonaro, Maury Markowitz, Maxim Razin, Maximus Rex, Mdanziger, Mgnbar, Michael C Price, Michael Hardy, Mira, Mishas42, Monedula, Mor, Moyogo, Mpatel,Mporter, Nn123645, Nonnormalizable, Nowhither, Ohwilleke, Pearle, Pharotic, Phys, PhysPhD, Plumpurple, Ptrslv72, Puzl bustr, QFT, R.e.b., RG2, RJFJR, Radagast83, Raul654, Reaverdrop,Rich Farmbrough, Rjwilmsi, Roadrunner, Robma, Roybb95, Rursus, Salgueiro, Sam Hocevar, Scrabby, SeventyThree, Sheliak, Smack, Solarapex, Stevertigo, Susy is it, Taw, Ted BJ, That Guy,From That Show!, TheMaster42, Theresa knott, TimothyRias, Tktktk, TriTertButoxy, Tweet Tweet, Unconcerned, VermillionBird, Vyroglyph, Wangjiaji, Wavelength, WikHead, Wtmitchell,Xerxes314, Xiaphias, Yevgeny Kats, Zahd, Zentropa77, 168 anonymous edits

Higgs boson  Source: http://en.wikipedia.org/w/index.php?oldid=407584584  Contributors: -dennis-, 1ForTheMoney, A Man In Black, A. di M., ABF, Aardvark23, Abdullais4u, Adrideba,Aknochel, Alansohn, Allstarecho, Altenmann, Alyjack, AnOddName, Anaxial, AndersFeder, AndrewN, Andrius.v, Angelo souti, AnonMoos, Anonymi, Antixt, Archelon, Art LaPella, Artur80,Asmeurer, Atomicthumbs, AxelBoldt, Baad, Bambaiah, Bbbl67, Bcody80, Bcorr, BenRG, Bender235, Benplowman, Betterusername, Bevo, Big Brother 1984, Biker Biker, Bjankuloski06en,BobertWABC, Bodhitha, Bookofjude, Boson15, Brian Fenton, Brians, Bryan Derksen, Bubba73, BullRangifer, C S, CYD, Cadmasteradam, Caknuck, Calmer Waters, CamB424, CamB4242,CesarB, Cgd8d, Cgwaldman, CharlesC, Chetvorno, Chreod, Christopher Thomas, Chuckupd, Cinkcool, Closedmouth, Consumed Crustacean, CrazyInSane, Cructacean, D'Agosta, DBGustavson,DKqwerty, DMurphy, Daniel C, DannyDaWriter, Dante Alighieri, Dauto, Dave3457, David spector, Dbachmann, DeadlyMETAL, Deceglie, Dekker451, Dirkbb, Discospinster, Diza,Donarreiskoffer, DrGaellon, Dragon of the Pants, Dratman, Drmies, DÅ‚ugosz, EchetusXe, Edderso, Ehn, Eikern, El C, ElfQrin, Eliga, Endersdouble, Epastore, Er ouz, Eritain, Ernsts, Excirial,Fatram, Fiziker, Fleisher, Fleminra, Flyguy649, Foobar, Foober, Foonle77, Fotoni, Frglee, Frymaster, Fæ, GDallimore, Gaurav, Giandrea, Giftlite, Gil987, Gobbledygeek, Goethean, Golbez,Goudzovski, GregorB, Gurch, Gwib, Hadal, Hairy Dude, Harold f, Harp, Headbomb, Hellbus, Herbee, Heron, Higgshunter, Hippypink, I hate whitespace, Icairns, Iknowyourider, Ilmari Karonen,Impunv, Infestor, Irenan, Itinerant, Itinerant1, Iwpg, J M Rice, J mcandrews, J.delanoy, JCSantos, JTiago, JabberWok, Jacques Antoine, JasonAQuest, Jc odcsmf, Jde123, Jdigitalbath,Jehochman, Jezzabr, Jfromcanada, Jgwacker, Jimtpat, Jkl, JohnArmagh, Johnflux, Jomoal99, JonathanDP81, Jonburchel, Jor63, Joriki, JorisvS, Josh Cherry, Jpod2, Jtuggle, Justinrossetti,KHamsun, Kaihsu, KapilTagore, Kbdank71, Kbk, Kborland, Keith-264, Kencf0618, Kendrick7, Kenneth Dawson, Kgf0, Koavf, Kocio, Konor org, Kooo, Krioni, Kyng, La goutte de pluie,Lambiam, Laplacian, Laurascudder, Lee M, Lethe, Lewisxxxusa, LilHelpa, Linas, Logicat, Loves martyr, Lycurgus, M-Falcon, Mani1, Manning Bartlett, Manu.ajm, Marcel Kosko, Marcus Brute,Mark Foskey, Markdavid2000, Martaf, Martijn Hoekstra, Martinthoegersen, Mary at CERN, Maryhit, Master1228, Masterofpsi, Matan568, Maurice Carbonaro, McSly, McVities, Mcorazao,Meier99, Melchoir, Meldor, Merovingian, Mesons, Mgimpel, Michael C Price, Mike Peel, Mike Rosoft, Mindmatrix, Minimac, Moeron, Moose-32, Mukadderat, Mx3, Mxn, My76Strat,N4tur4le, Nafhan, NawlinWiki, NeilN, Netrapt, NeverWorker, Newone, Newzebras, Nightscream, Nihiltres, NikiAnna, Nimur, Nobleacuff, Nondisclosure, Norm mit, Northumbrian, Norvy,Novemberrain94, Now dance, fu.cker, dance!, Nsbinsnj, Nskillen, Nurg, Nuujinn, Oddz, Ohnoitsjamie, Onesius, Opkdx, Oreo Priest, Orionus, Owain, Pagw, Paine Ellsworth, Perfectlight,PeterTheWall, Peterbullockismyname, Phil Boswell, Philip Trueman, Photonh2o, Phys, PhysicsAboveAll, PhysicsGrad2013, Pie4all88, Pip2andahalf, Pizza1512, Praveen pillay, ProjeX,Proofreader77, Pulickkal, Quadell, Quasipalm, Quatschman, Qutezuce, R.e.b., Rangelov, Raoul NK, Reinoutr, Resonance cascade, RetiredUser2, Reuben, RevenDS, Rich Farmbrough, Rick7425,Rjwilmsi, Roadrunner, RobertG, Roman à clef, Ronstew, Rotiro, Rursus, Ruslik0, SCZenz, Safety Cap, Salsb, Sasquatch, Sbove, Sburke, ScAvenger, Schucker, Selva, ShaneCavanaugh,Shawn@garbett.org, Shimgray, Shirifan, Siswick, Sjdunn9, Slawojarek, Sligocki, Spemble, Splarka, SqueakBox, Srleffler, StAnselm, StaticGull, Steve Quinn, StevenVerstoep, Strait, Superm401,Tburket, Tbushman, Tdent, TeunSpaans, Tevatron, The Original Wildbear, The Thing That Should Not Be, TheBendster, Thor Waldsen, Three887, Thruston, Tide rolls, Tigga en, Tim Shuba,Tom12519, TotoBaggins, Tpbradbury, TriTertButoxy, Tritium6, Twas Now, Universalsuffrage, Usp, V1adis1av, Vanished user 03, Varlaam, WAS 4.250, WLU, Waldir, Weaselpit, Wiggles007,WikiUserPedia, Wikiborg, Wmlschlotterer, Wnt, Xerxes314, Yevgeny Kats, Ylee, Yoweigh, Zekemurdock, Zentropa, 528 anonymous edits

Safety of particle collisions at the Large Hadron Collider  Source: http://en.wikipedia.org/w/index.php?oldid=390916998  Contributors: 2over0, Ageekgal, Alansohn, Alexius08,Allemandtando, Andrew Nutter, Annoyed with fanboys, Apalsola, Apparition11, Artichoker, Atkinson 291, Ayrton Prost, B7T, BCEagle21, Barak Sh, Baronnet, BenRG, Blehfu, Blueknightex,Bobo192, Boccobrock, BoogieRock, Bovineone, Bubba73, Bytbox, Canberra User, Cgingold, Chovain, Closedmouth, Cmpd1, Colonel Warden, ConspiracyFAIL, Conte0, Contribut, Cybercobra,DannyDaWriter, Darkensei, Darkoneko, Darrenhusted, Davidbeaumont, Dayewalker, Dferg, Dkasak, Dr.K., Dustand, Eaefremov, Eeekster, Elonka, Emmalouise99, Excirial, FeanorStar7,Feedahungryhippo, Fetchcomms, Fieldday-sunday, Fred Stober, Frostlion, Furrykef, Gazimoff, General Epitaph, GregorB, HaeB, Headbomb, Hqb, HumanJHawkins, Ilikefood, Ilmari Karonen,IngerAlHaosului, Islander, J.delanoy, Jalabi99, James Frankcom, Jamie C, Jeffq, Jehochman, John Nevard, Johnson Lau, Jonathan Drain, Joshua P. Schroeder, Jtankers, Jtrainor, Jwoodger,Kevin, Khukri, Koavf, Lfh, MMS2013, Mandarax, MarkTB, Maxime.Debosschere, Mcorazao, MickMacNee, Milesgillham, Million Moments, Miquonranger03, Mmerlo, Moondyne, NerdyNSK,Newone, Oldnoah, Orbnauticus, Orion11M87, Ormers, Patfrank, Perardi, Phenylalanine, PhySusie, Physchim62, Plasticup, Profgregory, Psychlohexane, Ptrslv72, RKT, Radical Mallard,RainbowOfLight, Rorro, SCZenz, SaveTheWhales, SheffieldSteel, Sizif, Smith609, SoSaysChappy, Sockatume, Sophus Bie, Sparrowgoose, SqueakBox, Stabby Joe, Staka, Steve Smith,Stevenfruitsmaak, Stevenj, Strait, Strayan, Swagmuncher, THEemu, Th1rt3en, The Anome, TheBilly, TheDoober, Thumperward, TimothyRias, Tombomp, TrevorX, Verbal, Vyznev Xnebara,Woohookitty, Wwheaton, XXOni-kunXx, Yar Kramer, Yellowdesk, 170 anonymous edits

Micro black hole  Source: http://en.wikipedia.org/w/index.php?oldid=406760957  Contributors: Againme, Aisphording, Antaeus Feldspar, Antixt, ArmAndLeg, Aswarp, Auric,BalanceRestored, Bender235, Bento00, Berndf, Blanchardb, Blue Tie, Bobwhitten, BradBeattie, Caco de vidro, Cacycle, Cam-Ann, Capricorn42, Chovain, Chris the speller, Christopher Thomas,Clarityfiend, Clark89, CrankyScorpion, Crunchy Numbers, D, Danielgrad, Deamon138, DeathNomad, Deb, Deconstructhis, Delldot, Discospinster, Diverman, DonJStevens, Donald Albury,Draugen, Dreadstar, EdC, Eequor, Egil, Ehn, El C, Email4mobile, Ersik, Esorbalo, FF2010, Fairandbalanced, FineCheeses, Fkara, Fleela, Giftlite, GraemeL, Gravitivistically, GregorB, Harel,Headbomb, Hellbus, Henrygb, IVAN3MAN, Iluvcapra, Ixfd64, JForget, Jack Merridew, Jamesontai, Jeff G., Jennavecia, Jheald, Jheise, Katieh5584, Khukri, Lainagier, Lenticel, Lethesl, Lightcurrent, Linas, Lysdexia, Mandarax, Martin-C, Mazarin07, Mckaysalisbury, Meelar, Melamed katz, Natecull, NonvocalScream, Norbi et Orbi, Nsaa, Numbo3, Oerjan, Olau, Oldnoah, Oni Lukos,Opie, Otus, Palpatine, Patrick, Paxfeline, Phenylalanine, Philip Trueman, Physprof, Pjf, Profgregory, Quasarq, Qxz, RBM 72, Radical Mallard, RayBirks, Rmrfstar, Roadrunner, Ronhjones, SJP,Sakkura, Scepia, Scootey, Scpark, Siener, Silverhill, Sinus, Skunkboy74, Smithbrenon, Snowolf, Spiralx, Supersheep, Sverdrup, Tarotcards, Teehee123, The Thing That Should Not Be, Thiseye,Timwi, Trilobite, Trilobitealive, Uiteoi, Utan Vax, V1adis1av, Vanisheduser12345, Velho, Vinsfan368, Viriditas, Wesino, Wiki alf, WikiFew, WurmWoode, XJamRastafire, Yettie0711,Zeimusu, 186 ,دمحأ anonymous edits

Strangelet  Source: http://en.wikipedia.org/w/index.php?oldid=407195955  Contributors: 3vil-Lyn, Army1987, Barak Sh, Barry Haworth, Brad Rousse, CharacterZero, Chkno, Chouca, Chovain,Christopher Thomas, Cybercobra, Danielgrad, Dark Formal, Dark Shikari, Darksun, Davidhorman, Demophon, Dmitry Brant, DomQ, Edvvc, Eyu100, Fourohfour, Gerasime, Gunark, Headbomb,Henry the 1st, Homocion, Hydraton31, Il Sc0rpi0ne, Insidepocket, It Is Me Here, Jackol, JarahE, Johann137, Johnthescavenger, Joquarky, Julesd, Justacec, Kgf0, Killing Vector, KungFuMonkey,Lainagier, Lethesl, Light current, LokiClock, Maxime.Debosschere, Mered4, Mjamja, MoeDrippins, NawlinWiki, Nfwu, NightmareZ, Nihiltres, OS2Warp, OlEnglish, Oldnoah, Oliver Pereira,Orange Suede Sofa, Oxymoron83, Pauli133, Petero9, Pgan002, Phenylalanine, Physchim62, PsychoJosh, Radical Mallard, Retodon8, Rich Farmbrough, Rickythesk8r, Robert Treat,Someguy1221, Specious, Squideshi, Suslindisambiguator, Takeshi Nakagawa, Taquito1, Twir, V1adis1av, Viapx, Werdna, Xanzzibar, Выползень, 148 anonymous edits

Super Large Hadron Collider  Source: http://en.wikipedia.org/w/index.php?oldid=397346881  Contributors: Astavats, BenRG, Bngrybt, Bobo192, Calwiki, Courcelles, DaL33T, Dbiel,Discospinster, Epbr123, Father McKenzie, Fieldday-sunday, Franamax, Fumitol, HEL, HappyArtichoke, Headbomb, Jasonbuzz, Kay Dekker, Khukri, Kocio, Laurascudder, Materialscientist,MaverickFurmeson, OlEnglish, QuantumShadow, Rjwilmsi, Rtomas, Seba5618, Shadowjams, Skizzik, Ste1n, TechnoFaye, The Anome, WriterHound, Ygrange, Zorx12, 86 anonymous edits

Very Large Hadron Collider  Source: http://en.wikipedia.org/w/index.php?oldid=398877677  Contributors: Aly89, Andrewa, Anna Lincoln, Astavats, Azcolvin429, Bevo, CoRdigALZ,Dbachmann, Fatal!ty, Grafen, Guy Thoreau, Halfdan, Headbomb, Iridescent, J.delanoy, JackSeoul, Joe446465446, Laurascudder, LeoNomis, Mac Davis, Northgrove, PMDrive1061, Ponty Pirate,Qwfp, RogueNinja, SCZenz, Salamurai, Science Guy, Seba5618, Skizzik, Tcncv, Verbal, ViperSnake151, WilliamH, Worm That Turned, XSG, Yin Huang, Zzuuzz, 45 anonymous edits

Image Sources, Licenses and Contributors 115

Image Sources, Licenses and ContributorsImage:CERN logo.svg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN_logo.svg  License: unknown  Contributors: SsolbergjImage:CERN member states.svg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN_member_states.svg  License: Creative Commons Attribution 3.0  Contributors: User:SsolbergjImage:Cernfounders.png  Source: http://en.wikipedia.org/w/index.php?title=File:Cernfounders.png  License: GNU Free Documentation License  Contributors: User:Hoshie, User:NerdyNSKImage:CERN1999.png  Source: http://en.wikipedia.org/w/index.php?title=File:CERN1999.png  License: GNU Free Documentation License  Contributors: User:NerdyNSKImage:First Web Server.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:First_Web_Server.jpg  License: unknown  Contributors: User:Coolcaesar at en.wikipediaImage:Ciscosystemsrouteratcern.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Ciscosystemsrouteratcern.jpg  License: GNU Free Documentation License  Contributors:CoolcaesarImage:Location Large Hadron Collider.PNG  Source: http://en.wikipedia.org/w/index.php?title=File:Location_Large_Hadron_Collider.PNG  License: Creative CommonsAttribution-Sharealike 2.0  Contributors: User:ZykureImage:Construction of LHC at CERN.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Construction_of_LHC_at_CERN.jpg  License: GNU Free Documentation License Contributors: Andrius.v, Deadstar, Square87Image:CERN-aerial.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN-aerial.jpg  License: Creative Commons Attribution-Sharealike 2.5  Contributors: Moumou82, Schutz,Túrelio, 3 anonymous editsImage:Bldng40cropped.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Bldng40cropped.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: Gillis DanielsenFile:Flag of Germany.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Germany.svg  License: Public Domain  Contributors: User:Madden, User:Pumbaa80, User:SKoppFile:Flag of France.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_France.svg  License: Public Domain  Contributors: User:SKopp, User:SKopp, User:SKopp, User:SKopp,User:SKopp, User:SKoppFile:Flag of the United Kingdom.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_United_Kingdom.svg  License: Public Domain  Contributors: User:Zscout370File:Flag of Italy.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Italy.svg  License: Public Domain  Contributors: see belowFile:Flag of Spain.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Spain.svg  License: Public Domain  Contributors: Pedro A. Gracia Fajardo, escudo de Manual de ImagenInstitucional de la Administración General del EstadoFile:Flag of the Netherlands.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_Netherlands.svg  License: Public Domain  Contributors: User:Zscout370File:Flag of Switzerland.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Switzerland.svg  License: Public Domain  Contributors: User:-xfi-, User:Marc Mongenet,User:Zscout370File:Flag of Poland.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Poland.svg  License: Public Domain  Contributors: User:Mareklug, User:WantedFile:Flag of Belgium (civil).svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Belgium_(civil).svg  License: Public Domain  Contributors: Bean49, David Descamps,Dbenbenn, Denelson83, Fry1989, Howcome, Ms2ger, Nightstallion, Oreo Priest, Rocket000, Sir Iain, ThomasPusch, Warddr, Zscout370, 3 anonymous editsFile:Flag of Sweden.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Sweden.svg  License: Public Domain  Contributors: User:Jon Harald SøbyFile:Flag of Norway.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Norway.svg  License: Public Domain  Contributors: User:DbenbennFile:Flag of Austria.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Austria.svg  License: Public Domain  Contributors: User:SKoppFile:Flag of Greece.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Greece.svg  License: Public Domain  Contributors: (of code) (talk)File:Flag of Denmark.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Denmark.svg  License: Public Domain  Contributors: User:MaddenFile:Flag of Finland.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Finland.svg  License: Public Domain  Contributors: User:SKoppFile:Flag of the Czech Republic.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_Czech_Republic.svg  License: Public Domain  Contributors: special commission (ofcode): SVG version by cs:-xfi-. Colors according to Appendix No. 3 of czech legal Act 3/1993. cs:Zirland.File:Flag of Portugal.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Portugal.svg  License: Public Domain  Contributors: User:NightstallionFile:Flag of Hungary.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Hungary.svg  License: Public Domain  Contributors: User:SKoppFile:Flag of Slovakia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Slovakia.svg  License: Public Domain  Contributors: User:SKoppFile:Flag of Bulgaria.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Bulgaria.svg  License: Public Domain  Contributors: Avala, Denelson83, Fry1989, Homo lupus,Ikonact, Kallerna, Klemen Kocjancic, Martyr, Mattes, Neq00, Pumbaa80, SKopp, Scroch, Serjio-pt, Spacebirdy, Srtxg, Ultratomio, Vonvon, Zscout370, 9 anonymous editsImage:CERN members.svg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN_members.svg  License: GNU Free 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http://en.wikipedia.org/w/index.php?title=File:Flag_of_Serbia.svg  License: Public Domain  Contributors: ABF, Avala, B1mbo, Denelson83, EDUCA33E,Herbythyme, Homo lupus, Imbris, Mormegil, Nightstallion, Nikola Smolenski, Nuno Gabriel Cabral, R-41, Rainman, Rokerismoravee, Sasa Stefanovic, Siebrand, ThomasPusch, Túrelio,Zscout370, 7 anonymous editsFile:Flag of Turkey.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Turkey.svg  License: Public Domain  Contributors: User:DbenbennFile:Flag of Israel.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Israel.svg  License: Public Domain  Contributors: AnonMoos, Bastique, Bobika, Brown spite, CaptainZizi, Cerveaugenie, Drork, Etams, Fred J, Fry1989, Geagea, Himasaram, Homo lupus, Humus sapiens, Klemen Kocjancic, Kookaburra, Luispihormiguero, Madden, Neq00, NielsF, Nightstallion,Oren neu dag, Patstuart, PeeJay2K3, Pumbaa80, Ramiy, Reisio, SKopp, Technion, Typhix, Valentinian, Yellow up, Zscout370, 31 anonymous editsFile:Flag of Russia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Russia.svg  License: Public Domain  Contributors: Zscout370File:Flag of Japan.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Japan.svg  License: Public Domain  Contributors: VariousFile:Flag of the United States.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_United_States.svg  License: Public Domain  Contributors: User:Dbenbenn,User:Indolences, User:Jacobolus, User:Technion, User:Zscout370File:Flag of India.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_India.svg  License: Public Domain  Contributors: User:SKoppFile:Flag of the United Nations.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_United_Nations.svg  License: Public Domain  Contributors: User:....File:Flag of Europe.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Europe.svg  License: Public Domain  Contributors: User:-xfi-, 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 Contributors: User:Zscout370File:Flag of Brazil.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Brazil.svg  License: Public Domain  Contributors: Brazilian GovernmentFile:Flag of Canada.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Canada.svg  License: Public Domain  Contributors: User:E Pluribus Anthony, User:MzajacFile:Flag of Chile.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Chile.svg  License: Public Domain  Contributors: User:SKopp

Image Sources, Licenses and Contributors 116

File:Flag of the People's Republic of China.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_People's_Republic_of_China.svg  License: Public Domain  Contributors:User:Denelson83, User:SKopp, User:Shizhao, User:Zscout370File:Flag of Colombia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Colombia.svg  License: Public Domain  Contributors: User:SKoppFile:Flag of Croatia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Croatia.svg  License: Public Domain  Contributors: AnyFile, Argo Navis, Denelson83, Denniss, Dijxtra,Klemen Kocjancic, Kseferovic, Minestrone, Multichill, Neoneo13, Nightstallion, O, PatríciaR, Platonides, R-41, Rainman, Reisio, Rocket000, Suradnik13, Zicera, Zscout370, 5 anonymous editsFile:Flag of Cuba.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Cuba.svg  License: Public Domain  Contributors: see belowFile:Flag of Cyprus.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Cyprus.svg  License: Public Domain  Contributors: AnonMoos, Bukk, Consta, Dbenbenn, Denelson83,Duduziq, Er Komandante, Homo lupus, Klemen Kocjancic, Krinkle, Mattes, NeoCy, Neq00, Nightstallion, Oleh Kernytskyi, Pumbaa80, Reisio, Telim tor, ThomasPusch, Vzb83, 15 anonymouseditsFile:Flag of Estonia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Estonia.svg  License: Public Domain  Contributors: User:PeepP, User:SKoppFile:Flag of Georgia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Georgia.svg  License: Public Domain  Contributors: User:SKoppFile:Flag of Iceland.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Iceland.svg  License: Public Domain  Contributors: User:Zscout370, User:Ævar Arnfjörð BjarmasonFile:Flag of Iran.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Iran.svg  License: unknown  Contributors: VariousFile:Flag of Ireland.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Ireland.svg  License: Public Domain  Contributors: User:SKoppFile:Flag of Lithuania.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Lithuania.svg  License: Public Domain  Contributors: User:SKoppFile:Flag of Macedonia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Macedonia.svg  License: Public Domain  Contributors: User:Gabbe, User:SKoppFile:Flag of Mexico.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Mexico.svg  License: Public Domain  Contributors: User:AlexCovarrubiasFile:Flag of Montenegro.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Montenegro.svg  License: Creative Commons Attribution-Sharealike 3.0  Contributors:User:B1mbo, User:FroztbyteFile:Flag of Morocco.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Morocco.svg  License: Public Domain  Contributors: User:Denelson83, User:Zscout370File:Flag of New Zealand.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_New_Zealand.svg  License: Public Domain  Contributors: Adambro, Arria Belli, Bawolff,Bjankuloski06en, ButterStick, Denelson83, Donk, Duduziq, EugeneZelenko, Fred J, Fry1989, Hugh Jass, Ibagli, Jusjih, Klemen Kocjancic, Mamndassan, Mattes, Nightstallion, O, Peeperman,Poromiami, Reisio, Rfc1394, Shizhao, Tabasco, Transparent Blue, Väsk, Xufanc, Zscout370, 35 anonymous editsFile:Flag of Pakistan.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Pakistan.svg  License: Public Domain  Contributors: Abaezriv, AnonMoos, Badseed, Dbenbenn,Duduziq, Fry1989, Gabbe, Himasaram, Homo lupus, Juiced lemon, Klemen Kocjancic, Mattes, Mollajutt, Neq00, Pumbaa80, Rfc1394, Srtxg, ThomasPusch, Túrelio, Zscout370, 9 anonymouseditsFile:Flag of Peru.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Peru.svg  License: Public Domain  Contributors: User:DbenbennFile:Flag of Slovenia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Slovenia.svg  License: Public Domain  Contributors: User:SKopp, User:Vzb83, User:Zscout370File:Flag of South Africa.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_South_Africa.svg  License: unknown  Contributors: Adriaan, Anime Addict AA, AnonMoos,BRUTE, Daemonic Kangaroo, Dnik, Duduziq, Dzordzm, Fry1989, Homo lupus, Jappalang, Juliancolton, Kam Solusar, Klemen Kocjancic, Klymene, Lexxyy, Mahahahaneapneap, Manuelt15,Moviedefender, Ninane, Poznaniak, SKopp, ThePCKid, ThomasPusch, Tvdm, Ultratomio, Vzb83, Zscout370, 33 anonymous editsFile:Flag of South Korea.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_South_Korea.svg  License: Public Domain  Contributors: VariousFile:Flag of the Republic of China.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_Republic_of_China.svg  License: Public Domain  Contributors: 555, Bestalex,Bigmorr, Denelson83, Ed veg, Gzdavidwong, Herbythyme, Isletakee, Kakoui, Kallerna, Kibinsky, Mattes, Mizunoryu, Neq00, Nickpo, Nightstallion, Odder, Pymouss, R.O.C, Reisio, Reuvenk,Rkt2312, Rocket000, Runningfridgesrule, Samwingkit, Sasha Krotov, Shizhao, Tabasco, Vzb83, Wrightbus, Zscout370, 72 anonymous editsFile:Flag of Thailand.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Thailand.svg  License: Public Domain  Contributors: Andy Dingley, Chaddy, Duduziq, Emerentia,Gabbe, Gurch, Homo lupus, Juiced lemon, Klemen Kocjancic, Mattes, Neq00, Paul 012, Rugby471, Sahapon-krit hellokitty, TOR, Teetaweepo, Xiengyod, Zscout370, Δ, 22 anonymous editsFile:Flag of Ukraine.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Ukraine.svg  License: Public Domain  Contributors: User:Jon Harald Søby, User:Zscout370File:Flag of Vietnam.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Vietnam.svg  License: Public Domain  Contributors: user:Lưu LyImage:CERN Globe of Science and Innovation.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN_Globe_of_Science_and_Innovation.jpg  License: Creative CommonsAttribution-Sharealike 2.0  Contributors: Lysippos, TomAltImage:LHC.svg  Source: http://en.wikipedia.org/w/index.php?title=File:LHC.svg  License: Creative Commons Attribution-Sharealike 2.5  Contributors: User:HarpFile:CMS Higgs-event.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:CMS_Higgs-event.jpg  License: unknown  Contributors: Lucas TaylorFile:BosonFusion-Higgs.svg  Source: http://en.wikipedia.org/w/index.php?title=File:BosonFusion-Higgs.svg  License: GNU Free Documentation License  Contributors: User:Booyabazooka,User:HarpFile:Location Large Hadron Collider.PNG  Source: http://en.wikipedia.org/w/index.php?title=File:Location_Large_Hadron_Collider.PNG  License: Creative Commons Attribution-Sharealike2.0  Contributors: User:ZykureFile:LHC quadrupole magnets.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:LHC_quadrupole_magnets.jpg  License: Creative Commons Attribution 2.0  Contributors: Andrius.vFile:Construction of LHC at CERN.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Construction_of_LHC_at_CERN.jpg  License: GNU Free Documentation License Contributors: Andrius.v, Deadstar, Square87Image:ALICE Detector.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:ALICE_Detector.jpg  License: Public Domain  Contributors: Original uploader was Connor Behan aten.wikipediaImage:ATLAS-logo.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:ATLAS-logo.jpg  License: unknown  Contributors: Andrius.v, MelesseImage:CERN Atlas Caverne.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN_Atlas_Caverne.jpg  License: GNU Free Documentation License  Contributors: Nikolai SchwergImage:gg to ttH.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Gg_to_ttH.jpg  License: Public Domain  Contributors: Ephraim33, Harp, Helix84, Joelholdsworth, Perhelion, PieterKuiper, SetresetImage:ATLAS TRT.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:ATLAS_TRT.jpg  License: GNU Free Documentation License  Contributors: Gorgo, HarpImage:ATLAS HCal.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:ATLAS_HCal.jpg  License: GNU Free Documentation License  Contributors: Mdd, Pieter Kuiper, Skaller, 1anonymous editsImage:CERN-Rama-33.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN-Rama-33.jpg  License: Creative Commons Attribution-Sharealike 2.0  Contributors: User:RamaImage:ATLAS Above.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:ATLAS_Above.jpg  License: GNU Free Documentation License  Contributors: Gorgo, HarpImage:Atlas detector CERN feb2007.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Atlas_detector_CERN_feb2007.jpg  License: Public Domain  Contributors: Sindre SkredeImage:CMS Under Construction Apr 05.jpg  Source: 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Boreham

Image Sources, Licenses and Contributors 117

Image:Insertion of vac-tank 2.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Insertion_of_vac-tank_2.jpg  License: unknown  Contributors: Harp, Luxo, WikipediaMasterImage:CMS Yep2 descent.gif  Source: http://en.wikipedia.org/w/index.php?title=File:CMS_Yep2_descent.gif  License: unknown  Contributors: webcamImage:YE Plus1 descends into cavern.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:YE_Plus1_descends_into_cavern.jpg  License: unknown  Contributors: Max Brice (?)Image:Run62063ev2433.png  Source: http://en.wikipedia.org/w/index.php?title=File:Run62063ev2433.png  License: unknown  Contributors: CMS CollaborationImage:Lhcbview.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Lhcbview.jpg  License: Public Domain  Contributors: HarpImage:LHCf.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:LHCf.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: User:AlbyImage:Beetle ASIC.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Beetle_ASIC.jpg  License: Public Domain  Contributors: LaroschImage:Standard Model of Elementary Particles.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Standard_Model_of_Elementary_Particles.svg  License: Creative CommonsAttribution 3.0  Contributors: User:MissMJImage:Elementary particle interactions.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Elementary_particle_interactions.svg  License: unknown  Contributors: User:StanneredImage:Particle chart Log.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Particle_chart_Log.svg  License: Public Domain  Contributors: Arivero, 1 anonymous editsImage:First Gold Beam-Beam Collision Events at RHIC at 100 100 GeV c per beam recorded by STAR.jpg  Source:http://en.wikipedia.org/w/index.php?title=File:First_Gold_Beam-Beam_Collision_Events_at_RHIC_at_100_100_GeV_c_per_beam_recorded_by_STAR.jpg  License: Creative CommonsAttribution-Sharealike 2.0  Contributors: Dbc334, Dmgultekin, Doodledoo, FlickreviewR, HAH, Herald Alberich, Kuaile Long, Odie5533, Romanm, Roomba, Saperaud, Yarnalgo, 4 anonymouseditsImage:Hqmc-vector.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Hqmc-vector.svg  License: Creative Commons Attribution 3.0  Contributors: User:VermillionBirdFile:AIP-Sakurai-best.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:AIP-Sakurai-best.JPG  License: Public Domain  Contributors: selfImage:One-loop-diagram.svg  Source: http://en.wikipedia.org/w/index.php?title=File:One-loop-diagram.svg  License: GNU Free Documentation License  Contributors: JabberWokImage:HiggsGraph 07-26-2010 hr.svg  Source: http://en.wikipedia.org/w/index.php?title=File:HiggsGraph_07-26-2010_hr.svg  License: Creative Commons Attribution-Sharealike 3.0 Contributors: User:JohnFluxImage:Gluon-top-higgs.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Gluon-top-higgs.svg  License: GNU Free Documentation License  Contributors:http://en.wikipedia.org/wiki/User:JabberWokImage:BosonFusion-Higgs.svg  Source: http://en.wikipedia.org/w/index.php?title=File:BosonFusion-Higgs.svg  License: GNU Free Documentation License  Contributors: User:Booyabazooka,User:HarpImage:CMS Higgs-event.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:CMS_Higgs-event.jpg  License: unknown  Contributors: Lucas Taylor

License 118

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