AsectionoftheLHC

LargeHadronCollider(LHC)

LHCexperiments

ATLAS AToroidalLHCApparatus

CMS CompactMuonSolenoid

LHCb LHCbeauty

ALICE ALargeIonColliderExperiment

TOTEM TotalCrossSection,ElasticScatteringandDiffractionDissociation

LHCf LHCforward

MoEDAL MonopoleandExoticsDetectorAttheLHC

LHCpreaccelerators

pandPb Linearacceleratorsforprotons(Linac2)andLead(Linac3)

(notmarked) ProtonSynchrotronBooster

LargeHadronColliderFromWikipedia,thefreeencyclopedia

TheLargeHadronCollider(LHC)istheworld'slargestandmostpowerfulparticlecollider,thelargestandmostcomplexexperimentalfacilityeverbuilt,andthelargestsinglemachineintheworld.[1]ItwasbuiltbytheEuropeanOrganizationforNuclearResearch(CERN)between1998and2008incollaborationwithover10,000scientistsandengineersfromover100countries,aswellashundredsofuniversitiesandlaboratories.[2]Itliesinatunnel27kilometres(17mi)incircumference,asdeepas175metres(574ft)beneaththeFrancoSwissbordernearGeneva,Switzerland.Itsfirstresearchruntookplacefrom30March2010to13February2013ataninitialenergyof3.5teraelectronvolts(TeV)perbeam(7TeVtotal),almost4timesmorethanthepreviousworldrecordforacollider,[3]risingto4TeVperbeam(8TeVtotal)from2012.[4][5]On13February2013theLHC'sfirstrunofficiallyended,anditwasshutdownforplannedupgrades.'Test'collisionsrestartedintheupgradedcollideron5April2015,[6][7]reaching6.5TeVperbeamon20May2015(13TeVtotal,thecurrentworldrecordforparticlecollisions).Itssecondresearchruncommencedonschedule,on3June2015.[8]

TheLHC'saimistoallowphysiciststotestthepredictionsofdifferenttheoriesofparticlephysics,highenergyphysicsandinparticular,toproveordisprovetheexistenceofthetheorizedHiggsboson[9]andthelargefamilyofnewparticlespredictedbysupersymmetrictheories,[10]andotherunsolvedquestionsofphysics,advancinghumanunderstandingofphysicallaws.Itcontainssevendetectors,eachdesignedforcertainkindsofresearch.Theprotonprotoncollisionistheprimaryoperationmethod,buttheLHChasalsocollidedprotonswithleadnucleifortwomonthsin2013andusedleadleadcollisionsforaboutonemontheachin2010,2011,and2013forotherinvestigations.

TheLHC'scomputinggridwas(andcurrentlyis)aworldrecordholder.Datafromcollisionswasanticipatedtobeproducedatanunprecedentedrateforthetime,oftensofpetabytesperyear,amajorchallengeatthetime,tobeanalysedbyagridbased

Coordinates:4614N0603E

PS ProtonSynchrotron

SPS SuperProtonSynchrotron

Hadroncolliders

IntersectingStorageRings CERN,19711984

SuperProtonSynchrotron CERN,19811984

ISABELLE BNL,cancelledin1983

Tevatron Fermilab,19872011

RelativisticHeavyIonCollider

BNL,2000present

SuperconductingSuperCollider

Cancelledin1993

LargeHadronCollider CERN,2009present

VeryLargeHadronCollider

Theoretical

computernetworkinfrastructureconnecting140computingcentersin35countries[11][12]by2012theWorldwideLHCComputingGridwasalsotheworld'slargestdistributedcomputinggrid,comprisingover170computingfacilitiesinaworldwidenetworkacross36countries.[13][14][15]

Contents

1Background2Purpose3Design

3.1Detectors3.2Computingandanalysisfacilities

4Operationalhistory4.1Construction

4.1.1Operationalchallenges4.1.2Cost4.1.3Constructionaccidentsanddelays4.1.4Initiallowercurrents

4.2Inauguraltests(2008)4.2.1Quenchincident

4.3Firstoperationalrun(20102013)4.4Upgrade(20132015)4.5Secondoperationalrun(2015onward)

5Timelineofoperations6Findingsanddiscoveries

6.1Firstrun(datataken20092013)6.2Secondrun(2015onward)

7Planned"highluminosity"upgrade8Safetyofparticlecollisions9Popularculture10Seealso11References12Externallinks

Background

Thetermhadronreferstocompositeparticlescomposedofquarksheldtogetherbythestrongforce(asatomsandmoleculesareheldtogetherbytheelectromagneticforce).Thebestknownhadronsarethebaryonsprotonsandneutronshadronsalsoincludemesonssuchasthepionandkaon,whichwerediscoveredduringcosmicrayexperimentsinthelate1940sandearly1950s.

Acolliderisatypeofaparticleacceleratorwithtwodirectedbeamsofparticles.Inparticlephysicscollidersareusedasaresearchtool:theyaccelerateparticlestoveryhighkineticenergiesandletthemimpactotherparticles.Analysisofthebyproductsofthesecollisionsgivesscientistsgoodevidenceof

thestructureofthesubatomicworldandthelawsofnaturegoverningit.Manyofthesebyproductsareproducedonlybyhighenergycollisions,andtheydecayafterveryshortperiodsoftime.Thusmanyofthemarehardornearimpossibletostudyinotherways.

Purpose

PhysicistshopethattheLHCwillhelpanswersomeofthefundamentalopenquestionsinphysics,concerningthebasiclawsgoverningtheinteractionsandforcesamongtheelementaryobjects,thedeepstructureofspaceandtime,andinparticulartheinterrelationbetweenquantummechanicsandgeneralrelativity,wherecurrenttheoriesandknowledgeareunclearorbreakdownaltogether.DataisalsoneededfromhighenergyparticleexperimentstosuggestwhichversionsofcurrentscientificmodelsaremorelikelytobecorrectinparticulartochoosebetweentheStandardModelandHiggslessmodelsandtovalidatetheirpredictionsandallowfurthertheoreticaldevelopment.ManytheoristsexpectnewphysicsbeyondtheStandardModeltoemergeattheTeVenergylevel,astheStandardModelappearstobeunsatisfactory.IssuespossiblytobeexploredbyLHCcollisionsinclude:[16][17]

ArethemassesofelementaryparticlesactuallygeneratedbytheHiggsmechanismviaelectroweaksymmetrybreaking?[18]ItisexpectedthatthecolliderwilleitherdemonstrateorruleouttheexistenceoftheelusiveHiggsboson,therebyallowingphysiciststoconsiderwhethertheStandardModeloritsHiggslessalternativesaremorelikelytobecorrect.[19][20][21]Issupersymmetry,anextensionoftheStandardModelandPoincarsymmetry,realizedinnature,implyingthatallknownparticleshavesupersymmetricpartners?[22][23][24]

Arethereextradimensions,[25]aspredictedbyvariousmodelsbasedonstringtheory,andcanwedetectthem?[26]Whatisthenatureofthedarkmatterthatappearstoaccountfor27%ofthemassenergyoftheuniverse?

Otheropenquestionsthatmaybeexploredusinghighenergyparticlecollisions:

Itisalreadyknownthatelectromagnetismandtheweaknuclearforcearedifferentmanifestationsofasingleforcecalledtheelectroweakforce.TheLHCmayclarifywhethertheelectroweakforceandthestrongnuclearforcearesimilarlyjustdifferentmanifestationsofoneuniversalunifiedforce,aspredictedbyvariousGrandUnificationTheories.Whyisthefourthfundamentalforce(gravity)somanyordersofmagnitudeweakerthantheotherthreefundamentalforces?SeealsoHierarchyproblem.Arethereadditionalsourcesofquarkflavourmixing,beyondthosealreadypresentwithintheStandardModel?Whyarethereapparentviolationsofthesymmetrybetweenmatterandantimatter?SeealsoCPviolation.Whatarethenatureandpropertiesofquarkgluonplasma,thoughttohaveexistedintheearlyuniverseandincertaincompactandstrangeastronomicalobjectstoday?Thiswillbeinvestigatedbyheavyioncollisions,mainlyinALICE,butalsoinCMSandATLAS.Findingspublishedin2012confirmedthephenomenonofjetquenchinginheavyioncollisions,andwasfirstobservedin2010.[27][28][29]

Design

TheLHCistheworld'slargestandhighestenergyparticleaccelerator.[30][31]Thecollideriscontainedinacirculartunnel,withacircumferenceof27kilometres(17mi),atadepthrangingfrom50to175metres(164to574ft)underground.

AFeynmandiagramofonewaytheHiggsbosonmaybeproducedattheLHC.Here,twoquarkseachemitaWorZboson,whichcombinetomakeaneutralHiggs. MapoftheLargeHadronColliderat

CERN

The2in1structureoftheLHCdipolemagnets

Superconductingquadrupoleelectromagnetsareusedtodirectthebeamstofourintersectionpoints,whereinteractionsbetweenacceleratedprotonswilltakeplace.

The3.8metre(12ft)wideconcretelinedtunnel,constructedbetween1983and1988,wasformerlyusedtohousetheLargeElectronPositronCollider.[32]ItcrossestheborderbetweenSwitzerlandandFranceatfourpoints,withmostofitinFrance.Surfacebuildingsholdancillaryequipmentsuchas

compressors,ventilationequipment,controlelectronicsandrefrigerationplants.

Thecollidertunnelcontainstwoadjacentparallelbeamlines(orbeampipes)thatintersectatfourpoints,eachcontainingabeam,whichtravelinoppositedirectionsaroundthering.Some1,232dipolemagnetskeepthebeamsontheir

circularpath(seeimage[33]),whileanadditional392quadrupolemagnetsareusedtokeepthebeamsfocused,inordertomaximizethechancesofinteractionbetweentheparticlesinthefourintersectionpoints,wherethetwobeamscross.Intotal,over1,600superconductingmagnetsareinstalled,withmostweighingover27tonnes.[34]Approximately96tonnesofsuperfluidhelium4isneededtokeepthemagnets,madeofcoppercladniobiumtitanium,attheiroperatingtemperatureof1.9K(271.25C),makingtheLHCthelargestcryogenicfacilityintheworldatliquidheliumtemperature.

Whenrunningatfulldesignenergyof7TeVperbeam,onceortwiceaday,astheprotonsareacceleratedfrom450GeVto7TeV,thefieldofthesuperconductingdipolemagnetswillbeincreasedfrom0.54to8.3teslas(T).Theprotonswilleachhaveanenergyof7TeV,givingatotalcollisionenergyof14TeV.AtthisenergytheprotonshaveaLorentzfactorofabout7,500andmoveatabout0.999 999 991c,orabout3metrespersecondslowerthanthespeedoflight(c).[35]Itwilltakelessthan90microseconds(s)foraprotontotraveloncearoundthemainringaspeedofabout11,000revolutionspersecond.Ratherthancontinuousbeams,theprotonswillbebunchedtogether,intoupto2,808bunches,with115billionprotonsineachbunchsothatinteractionsbetweenthetwobeamswilltakeplaceatdiscreteintervals,mainly25nanoseconds(ns)apart,providinga

bunchcollisionrateof40MHz.Howeveritwillbeoperatedwithfewerbuncheswhenitisfirstcommissioned,givingitabunchcrossingintervalof75ns.[36]ThedesignluminosityoftheLHCis1034

cm2s1.[37]

CMSdetectorforLHC

Priortobeinginjectedintothemainaccelerator,theparticlesarepreparedbyaseriesofsystemsthatsuccessivelyincreasetheirenergy.ThefirstsystemisthelinearparticleacceleratorLINAC2generating50MeVprotons,whichfeedstheProtonSynchrotronBooster(PSB).Theretheprotonsareacceleratedto1.4GeVandinjectedintotheProtonSynchrotron(PS),wheretheyareacceleratedto26GeV.FinallytheSuperProtonSynchrotron(SPS)isusedtofurtherincreasetheirenergyto450GeVbeforetheyareatlastinjected(overaperiodofseveralminutes)intothemainring.Heretheprotonbunchesareaccumulated,accelerated(overaperiodof20minutes)totheirpeakenergy,andfinallycirculatedfor5to24hourswhilecollisionsoccuratthefourintersectionpoints.[38]

TheLHCphysicsprogramismainlybasedonprotonprotoncollisions.However,shorterrunningperiods,typicallyonemonthperyear,withheavyioncollisionsareincludedintheprogram.Whilelighterionsareconsideredaswell,thebaselineschemedealswithleadions[39](seeALargeIonColliderExperiment).TheleadionsarefirstacceleratedbythelinearacceleratorLINAC3,andtheLowEnergyIonRing(LEIR)isusedasanionstorageandcoolerunit.TheionsarethenfurtheracceleratedbythePSandSPSbeforebeinginjectedintoLHCring,wheretheyreachedanenergyof1.58TeVpernucleon(or328TeVperion),higherthantheenergiesreachedbytheRelativisticHeavyIonCollider.Theaimoftheheavyionprogramistoinvestigatequarkgluonplasma,whichexistedintheearlyuniverse.

Detectors

SevendetectorshavebeenconstructedattheLHC,locatedundergroundinlargecavernsexcavatedattheLHC'sintersectionpoints.Twoofthem,theATLASexperimentandtheCompactMuonSolenoid(CMS),arelarge,generalpurposeparticledetectors.[31]ALICEandLHCbhavemorespecificrolesandthelastthree,TOTEM,MoEDALandLHCf,areverymuchsmallerandareforveryspecializedresearch.TheBBC'ssummaryofthemaindetectorsis:[40]

Detector Description

ATLAS Oneoftwogeneralpurposedetectors.ATLASwillbeusedtolookforsignsofnewphysics,includingtheoriginsofmassandextradimensions.

CMS Theothergeneralpurposedetectorwill,likeATLAS,huntfortheHiggsbosonandlookforcluestothenatureofdarkmatter.

ALICE ALICEisstudyinga"fluid"formofmattercalledquarkgluonplasmathatexistedshortlyaftertheBigBang.

LHCb EqualamountsofmatterandantimatterwerecreatedintheBigBang.LHCbwilltrytoinvestigatewhathappenedtothe"missing"antimatter.

Computingandanalysisfacilities

DataproducedbyLHC,aswellasLHCrelatedsimulation,wasestimatedatapproximately15petabytesperyear(maxthroughputwhilerunningnotstated)[41]amajorchallengeinitsownrightatthetime.

TheLHCComputingGrid[42]wasconstructedaspartoftheLHCdesign,tohandlethemassiveamountsofdataexpectedforitscollisions.Itisaninternationalcollaborativeprojectthatconsistsofagridbasedcomputernetworkinfrastructureinitiallyconnecting140computingcentersin35countries(over170in36countriesasof2012).ItwasdesignedbyCERNtohandlethesignificantvolumeofdataproducedby

LHCexperiments,[11][12]incorporatingbothprivatefiberopticcablelinksandexistinghighspeedportionsofthepublicInternettoenabledatatransferfromCERNtoacademicinstitutionsaroundtheworld.[43]TheOpenScienceGridisusedastheprimaryinfrastructureintheUnitedStates,andalsoaspartofaninteroperablefederationwiththeLHCComputingGrid.

ThedistributedcomputingprojectLHC@homewasstartedtosupporttheconstructionandcalibrationoftheLHC.TheprojectusestheBOINCplatform,enablinganybodywithanInternetconnectionandacomputerrunningMacOSX,WindowsorLinux,tousetheircomputer'sidletimetosimulatehowparticleswilltravelinthetunnel.Withthisinformation,thescientistswillbeabletodeterminehowthemagnetsshouldbecalibratedtogainthemoststable"orbit"ofthebeamsinthering.[44]InAugust2011,asecondapplicationwentlive(Test4Theory)whichperformssimulationsagainstwhichtocompareactualtestdata,todetermineconfidencelevelsoftheresults.

By2012datafromover6quadrillion(6x1015)LHCprotonprotoncollisionshadbeenanalyzed,[45]LHCcollisiondatawasbeingproducedatapproximately25petabytesperyear,andtheLHCComputingGridhadbecometheworld'slargestcomputinggrid(asof2012),comprisingover170computingfacilitiesinaworldwidenetworkacross36countries.[13][14][15]

Operationalhistory

TheLHCfirstwentliveon10September2008,butinitialtestingwasdelayedfor14monthsfrom19September2008to20November2009,followingamagnetquenchincidentthatcausedextensivedamagetoover50superconductingmagnets,theirmountings,andthevacuumpipe.[46][47][48][49][50][51]

Duringitsfirstrun(20102013)theLHCcollidedtwoopposingparticlebeamsofeitherprotonsatupto4teraelectronvolts(4TeVor0.64microjoules),orleadnuclei(574TeVpernucleus,or2.76TeVpernucleon).[30][52]ItsfirstrundiscoveriesincludedaparticlethoughttobethelongsoughtHiggsboson,severalcompositeparticles(hadrons)liketheb(3P)bottomoniumstate,thefirstcreationofaquark

gluonplasma,andthefirstobservationsoftheveryraredecayoftheBsmesonintotwomuons(Bs0+),whichchallengedthevalidityofexistingmodelsofsupersymmetry.[53]

Construction

Operationalchallenges

ThesizeoftheLHCconstitutesanexceptionalengineeringchallengewithuniqueoperationalissuesonaccountoftheamountofenergystoredinthemagnetsandthebeams.[38][54]Whileoperating,thetotalenergystoredinthemagnetsis10GJ(2,400kilogramsofTNT)andthetotalenergycarriedbythetwobeamsreaches724MJ(173kilogramsofTNT).[55]

Lossofonlyonetenmillionthpart(107)ofthebeamissufficienttoquenchasuperconductingmagnet,whilethebeamdumpmustabsorb362MJ(87kilogramsofTNT)foreachofthetwobeams.Theseenergiesarecarriedbyverylittlematter:undernominaloperatingconditions(2,808bunchesperbeam,1.151011protonsperbunch),thebeampipescontain1.0109gramofhydrogen,which,instandardconditionsfortemperatureandpressure,wouldfillthevolumeofonegrainoffinesand.

Cost

Withabudgetof7.5billioneuros(approx.$9bnor6.19bnasofJune2010),theLHCisoneofthemostexpensivescientificinstruments[56]everbuilt.[57]Thetotalcostoftheprojectisexpectedtobeoftheorderof4.6bnSwissfrancs(SFr)(approx.$4.4bn,3.1bn,or2.8bnasofJan2010)fortheacceleratorand1.16bn(SFr)(approx.$1.1bn,0.8bn,or0.7bnasofJan2010)fortheCERNcontributiontotheexperiments.[58]

TheconstructionofLHCwasapprovedin1995withabudgetofSFr2.6bn,withanotherSFr210Mtowardstheexperiments.However,costoverruns,estimatedinamajorreviewin2001ataroundSFr480Mfortheaccelerator,andSFr50Mfortheexperiments,alongwithareductioninCERN'sbudget,pushedthecompletiondatefrom2005toApril2007.[59]ThesuperconductingmagnetswereresponsibleforSFr180Mofthecostincrease.TherewerealsofurthercostsanddelaysduetoengineeringdifficultiesencounteredwhilebuildingtheundergroundcavernfortheCompactMuonSolenoid,[60]andalsoduetomagnetsupportswhichwereinsufficientlystronglydesignedandfailedtheirinitialtesting(2007)anddamagefromamagnetquenchandliquidheliumescape(inauguraltesting,2008)(see:Constructionaccidentsanddelays).[61]Duetolowerelectricitycostsduringthesummer,theLHCnormallydoesnotoperateoverthewintermonths,[62]althoughanexceptionoverthe2009/10winterwasmadetomakeupforthe2008startupdelays.

Constructionaccidentsanddelays

On25October2005,JosPereiraLages,atechnician,waskilledintheLHCwhenaswitchgearthatwasbeingtransportedfellonhim.[63]On27March2007acryogenicmagnetsupportdesignedandprovidedbyFermilabandKEKbrokeduringaninitialpressuretestinvolvingoneoftheLHC'sinnertriplet(focusingquadrupole)magnetassemblies.Noonewasinjured.FermilabdirectorPierOddonestated"Inthiscasewearedumbfoundedthatwemissedsomeverysimplebalanceofforces".Thisfaulthadbeenpresentintheoriginaldesign,andremainedduringfourengineeringreviewsoverthefollowingyears.[64]Analysisrevealedthatitsdesign,madeasthinaspossibleforbetterinsulation,wasnotstrongenoughtowithstandtheforcesgeneratedduringpressuretesting.DetailsareavailableinastatementfromFermilab,withwhichCERNisinagreement.[65][66]RepairingthebrokenmagnetandreinforcingtheeightidenticalassembliesusedbyLHCdelayedthestartupdate,thenplannedforNovember2007.On19September2008,duringinitialtesting,afaultyelectricalconnectionledtoamagnetquench(thesuddenlossofasuperconductingmagnet'ssuperconductingabilityduetowarmingorelectricfieldeffects).Sixtonnesofsupercooledliquidheliumusedtocoolthemagnetsescaped,withsufficientforcetobreak10tonmagnetsnearbyfromtheirmountings,andcausedconsiderabledamageandcontaminationofthevacuumtube(see2008quenchincident)repairsandsafetycheckscausedadelayofaround14months.[67][68][69]TwovacuumleakswereidentifiedinJuly2009,andthestartofoperationswasfurtherpostponedtomidNovember2009.[70]

Initiallowercurrents

Inbothofitsruns(2010and2015),theLHCwasinitiallyrunatenergiesbelowitsplannedoperatingenergy,andrampeduptojust2x3.5TeVenergyonitsfirstrun(final2x4TeV),and2x6.5TeVonitssecondrun(intended:2x7TeV).Thisisbecausemassivesuperconductingmagnetsrequireconsiderablemagnettrainingtohandlethehighcurrentsinvolvedwithoutlosingtheirsuperconductingability.The"training"processinvolvesrepeatedlyrunningthemagnetswithlowercurrentstoprovokeanyquenchesorminutemovementsthatmayresult.Italsotakestimetocooldownmagnetstotheiroperatingtemperatureofaround1.9K(degreesaboveabsolutezero).Overtimethemagnet"bedsin"

Wikinewshasrelatednews:CERNsaysrepairstoLHCparticleacceleratortocost16.6million

andceasestoquenchattheselessercurrentsandcanhandlethefulldesigncurrentwithoutquenchingCERNmediadescribethemagnetsas"shakingout"theunavoidabletinymanufacturingimperfectionsintheircrystalsandpositionsthathadinitiallyimpairedtheirabilitytohandletheirplannedcurrents.Themagnetsovertimeandwithtraining,graduallybecomeabletohandletheirfullplannedcurrentswithoutquenching.[71][72]

Inauguraltests(2008)

Thefirstbeamwascirculatedthroughthecollideronthemorningof10September2008.[40]CERNsuccessfullyfiredtheprotonsaroundthetunnelinstages,threekilometresatatime.Theparticleswerefiredinaclockwisedirectionintotheacceleratorandsuccessfullysteeredarounditat10:28localtime.[73]TheLHCsuccessfullycompleteditsmajortest:afteraseriesoftrialruns,twowhitedotsflashedonacomputerscreenshowingtheprotonstravelledthefulllengthofthecollider.Ittooklessthanonehourtoguidethestreamofparticlesarounditsinauguralcircuit.[74]CERNnextsuccessfullysentabeamofprotonsinacounterclockwisedirection,takingslightlylongeratoneandahalfhoursduetoaproblemwiththecryogenics,withthefullcircuitbeingcompletedat14:59.

Quenchincident

On19September2008,amagnetquenchoccurredinabout100bendingmagnetsinsectors3and4,whereanelectricalfaultledtoalossofapproximatelysixtonnesofliquidhelium(themagnets'cryogeniccoolant),whichwasventedintothetunnel.Theescapingvaporexpandedwithexplosiveforce,damagingover50superconductingmagnetsandtheirmountings,andcontaminatingthevacuumpipe,whichalsolostvacuumconditions.[47][48][75]

ShortlyaftertheincidentCERNreportedthatthemostlikelycauseoftheproblemwasafaultyelectricalconnectionbetweentwomagnets,andthatduetothetimeneededtowarmuptheaffectedsectorsandthencoolthembackdowntooperatingtemperatureitwouldtakeatleasttwomonthstofix.[76]CERNreleasedaninterimtechnicalreport[75]andpreliminaryanalysisoftheincidenton15and16October2008respectively,[77]andamoredetailedreporton5December2008.[68]TheanalysisoftheincidentbyCERNconfirmedthatanelectricalfaulthadindeedbeenthecause.Thefaultyelectricalconnectionhadled(correctly)toafailsafepowerabortoftheelectricalsystemspoweringthesuperconductingmagnets,buthadalsocausedanelectricarc(ordischarge)whichdamagedtheintegrityofthesupercooledhelium'senclosureandvacuuminsulation,causingthecoolant'stemperatureandpressuretorapidlyrisebeyondtheabilityofthesafetysystemstocontainit,[75]andleadingtoatemperatureriseofabout100degreesCelsiusinsomeoftheaffectedmagnets.Energystoredinthesuperconductingmagnetsandelectricalnoiseinducedinotherquenchdetectorsalsoplayedaroleintherapidheating.Aroundtwotonnesofliquidheliumescapedexplosivelybeforedetectorstriggeredanemergencystop,andafurtherfourtonnesleakedatlowerpressureintheaftermath.[75]Atotalof53magnetsweredamagedintheincidentandwererepairedorreplacedduringthewintershutdown.[78]Thisaccidentwasthoroughlydiscussedina22February2010SuperconductorScienceandTechnologyarticlebyCERNphysicistLucioRossi.[79]

IntheoriginaltimelineoftheLHCcommissioning,thefirst"modest"highenergycollisionsatacenterofmassenergyof900GeVwereexpectedtotakeplacebeforetheendofSeptember2008,andtheLHCwasexpectedtobeoperatingat10TeVbytheendof2008.[80]However,duetothedelaycausedbythe

abovementionedincident,thecolliderwasnotoperationaluntilNovember2009.[81]Despitethedelay,LHCwasofficiallyinauguratedon21October2008,inthepresenceofpoliticalleaders,scienceministersfromCERN's20MemberStates,CERNofficials,andmembersoftheworldwidescientificcommunity.[82]

Mostof2009wasspentonrepairsandreviewsfromthedamagecausedbythequenchincident,alongwithtwofurthervacuumleaksidentifiedinJuly2009whichpushedthestartofoperationstoNovemberofthatyear.[70]

Firstoperationalrun(20102013)

On20November2009,lowenergybeamscirculatedinthetunnelforthefirsttimesincetheincident,andshortlyafter,on30November,theLHCachieved1.18TeVperbeamtobecometheworld'shighestenergyparticleaccelerator,beatingtheTevatron'spreviousrecordof0.98TeVperbeamheldforeightyears.[83]

Theearlypartof2010sawthecontinuedrampupofbeaminenergiesandearlyphysicsexperimentstowards3.5TeVperbeamandon30March2010,LHCsetanewrecordforhighenergycollisionsbycollidingprotonbeamsatacombinedenergylevelof7TeV.Theattemptwasthethirdthatday,aftertwounsuccessfulattemptsinwhichtheprotonshadtobe"dumped"fromthecolliderandnewbeamshadtobeinjected.[84]Thisalsomarkedthestartofitsmainresearchprogram.

Thefirstprotonrunendedon4November2010.Arunwithleadionsstartedon8November2010,andendedon6December2010,[85]allowingtheALICEexperimenttostudymatterunderextremeconditionssimilartothoseshortlyaftertheBigBang.[86]

CERNoriginallyplannedthattheLHCwouldrunthroughtotheendof2012,withashortbreakattheendof2011toallowforanincreaseinbeamenergyfrom3.5to4TeVperbeam.[4]Attheendof2012theLHCwasshutdownuntilaround2015toallowupgradetoaplannedbeamenergyof7TeVperbeam.[87]Inlate2012,inlightoftheJuly2012discoveryoftheHiggsboson,theshutdownwaspostponedforsomeweeksintoearly2013,toallowadditionaldatatobeobtainedpriortoshutdown.

Upgrade(20132015)

TheLHCwasshutdownon13February2013foritsplanned2yearupgrade,whichwouldtouchonmanyaspectsoftheLHC:enablingcollisionsat14TeV,enhancingitsdetectorsandpreaccelerators(theProtonSynchrotronandSuperProtonSynchrotron),aswellasreplacingitsventilationsystemand100kmofcablingimpairedbyhighenergycollisionsfromitsfirstrun.[88]TheupgradedcolliderbeganitslongstartupandtestingprocessinJune2014,withtheProtonSynchrotronBoosterstartingon2June2014,thefinalinterconnectionbetweenmagnetscompletingandtheProtonSychrotroncirculatingparticleson18June2014,andthefirstsectionofthemainLHCsupermagnetsystemreachingoperatingtemperatureof1.91.9K(271.25C),afewdayslater.[89]ThefirstofthemainLHCsupermagnetswerereportedtohavebeensuccessfully"trained"torunat11,000amps(thecurrentrequiredfor6.5TeVcollisions)by9December2014,withtheothermagnetsectorsplannedtocompletetrainingbySpring2015.[90]

Secondoperationalrun(2015onward)

On5April2015theLHCrestartedafteratwoyearbreakduringwhichitwasextensivelyupgradedtorunatitsfullspecifiedoperatingenergiesof7TeVperbeam(14TeV),althoughinitiallyrunat6.5TeVperbeam(13TeVtotal)whilethemagnetsbeddedin(knownas"training").[6]Althoughparticlebeamstravelledinbothdirections,insideparallelpipes,actualcollisionswereexpectedtobegininJune.[6]Thefirstrampon10April2015gavepromisingresultsasitreached6.5TeV.[91]Theupgradesculminatedincollidingprotonstogetherwithacombinedenergyof13TeV.[92]On3June2015theLHCstarteddeliveringphysicsdataafteralmosttwoyearsoffline.[93]

Timelineofoperations

Date Event

10Sep2008 CERNsuccessfullyfiredthefirstprotonsaroundtheentiretunnelcircuitinstages.

19Sep2008 Magneticquenchoccurredinabout100bendingmagnetsinsectors3and4,causingalossofapproximately6tonnesofliquidhelium.

30Sep2008 First"modest"highenergycollisionsplannedbutpostponedduetoaccident.[34]

16Oct2008 CERNreleasedapreliminaryanalysisoftheaccident.21Oct2008 Officialinauguration.5Dec2008 CERNreleaseddetailedanalysis.

20Nov2009 Lowenergybeamscirculatedinthetunnelforthefirsttimesincetheaccident.[94]

23Nov2009 Firstparticlecollisionsinallfourdetectorsat450GeV.

30Nov2009LHCbecomestheworld'shighestenergyparticleacceleratorachieving1.18TeVperbeam,beatingtheTevatron'spreviousrecordof0.98TeVperbeamheldforeightyears.[83]

15Dec2009 Firstscientificresults,covering284collisionsintheALICEdetector.[95]

earlyFeb2010 FirstprotonprotoncollisionsbeyondFermiLab'senergies,publishedbytheCMSteam.[96]

28Feb2010TheLHCcontinuesoperationsrampingenergiestorunat3.5TeVfor18monthstotwoyears,afterwhichitwillbeshutdowntoprepareforthe14TeVcollisions(7TeVperbeam).[97]

30Mar2010 Thetwobeamscollidedat7TeV(3.5TeVperbeam)intheLHCat13:06CEST,markingthestartoftheLHCresearchprogram.8Nov2010 Startofthefirstrunwithleadions.6Dec2010 Endoftherunwithleadions.Shutdownuntilearly2011.

13Mar2011 Beginningofthe2011runwithprotonbeams.[98]

21Apr2011LHCbecomestheworld'shighestluminosityhadronacceleratorachievingapeakluminosityof4.671032cm2s1,beatingtheTevatron'spreviousrecordof41032cm2s1heldforoneyear.[99]

24May2011 Quarkgluonplasmaachieved.[100]

17Jun2011 ThehighluminosityexperimentsATLASandCMSreach1fb1of

collecteddata.[101]

14Oct2011 LHCbreaches1fb1ofcollecteddata.[102]

23Oct2011 ThehighluminosityexperimentsATLASandCMSreach5fb1of

collecteddata.

Nov2011 Secondrunwithleadions.

22Dec2011Firstnewcompositeparticlediscovery,theb(3P)bottomoniummeson,observedwithprotonprotoncollisionsin2011.[103]

5Apr2012 Firstcollisionswithstablebeamsin2012afterthewintershutdown.Theenergyisincreasedto4TeVperbeam(8TeVincollisions).[104]

4Jul2012Firstnewelementaryparticlediscovery,anewbosonobservedthatis"consistentwith"thetheorizedHiggsboson.(ThishasnowbeenconfirmedastheHiggsbosonitself.[105])

8Nov2012

FirstobservationoftheveryraredecayoftheBsmesonintotwomuons(Bs0+),amajortestofsupersymmetrytheories,[106]showsresultsat3.5sigmathatmatchtheStandardModelratherthanmanyofitssupersymmetricalvariants.

20Jan2013 StartofthefirstruncollidingprotonswithLeadions.11Feb2013 EndofthefirstruncollidingprotonswithLeadions.

14Feb2013Beginningofthefirstlongshutdown,topreparethecolliderforahigherenergyandluminosity.Whenreactivatedin2015,theLHCwilloperatewithanenergyof6.5TeVperproton.[107]

7Mar2015 InjectiontestsforRun2sendprotonstowardsLHCb&ALICE

5Apr2015 Bothbeamscirculatedinthecollider.[6]Fourdayslater,anewrecord

energyof6.5TeVperprotonwasachieved.[108]

20May2015 ProtonscollidedintheLHCattherecordbreakingenergyof13TeV.[92]

3June2015Startofdeliveringthephysicsdataafteralmosttwoyearsofflineforrecommissioning.[93]

Findingsanddiscoveries

AninitialfocusofresearchwastoinvestigatethepossibleexistenceoftheHiggsboson,akeypartoftheStandardModelofphysicswhichwaspredictedbytheorybuthadnotyetbeenobservedorproventoexistduetoitselusivenatureandexceedinglybrieflifespan.CERNscientistsestimatedthat,iftheStandardModelwerecorrect,theLHCwouldproduceseveralHiggsbosonseveryminute,allowingphysiciststofinallyconfirmordisprovetheHiggsbosonsexistence.Inaddition,theLHCallowedtosearchforsupersymmetricparticlesandotherhypotheticalparticlesaspossibleunknownareasofphysics.[30]SomeextensionsoftheStandardModelpredictadditionalparticles,suchastheheavyW'andZ'gaugebosons,whichwerealsoestimatedtobewithinreachoftheLHCtodiscover.[109]

Firstrun(datataken20092013)

ThefirstphysicsresultsfromtheLHC,involving284collisionswhichtookplaceintheALICEdetector,werereportedon15December2009.[95]TheresultsofthefirstprotonprotoncollisionsatenergieshigherthanFermilab'sTevatronprotonantiprotoncollisionswerepublishedbytheCMScollaborationinearlyFebruary2010,yieldinggreaterthanpredictedchargedhadronproduction.[96]

Afterthefirstyearofdatacollection,theLHCexperimentalcollaborationsstartedtoreleasetheirpreliminaryresultsconcerningsearchesfornewphysicsbeyondtheStandardModelinprotonprotoncollisions.[110][111][112][113]Noevidenceofnewparticleswasdetectedinthe2010data.Asaresult,

boundsweresetontheallowedparameterspaceofvariousextensionsoftheStandardModel,suchasmodelswithlargeextradimensions,constrainedversionsoftheMinimalSupersymmetricStandardModel,andothers.[114][115][116]

On24May2011,itwasreportedthatquarkgluonplasma(thedensestmatterthoughttoexistbesidesblackholes)hadbeencreatedintheLHC.[100]

BetweenJulyandAugust2011,resultsofsearchesfortheHiggsbosonandforexoticparticles,basedonthedatacollectedduringthefirsthalfofthe2011run,werepresentedinconferencesinGrenoble[117]

andMumbai.[118]Inthelatterconferenceitwasreportedthat,despitehintsofaHiggssignalinearlierdata,ATLASandCMSexcludewith95%confidencelevel(usingtheCLsmethod)theexistenceofaHiggsbosonwiththepropertiespredictedbytheStandardModelovermostofthemassregionbetween145and466GeV.[119]Thesearchesfornewparticlesdidnotyieldsignalseither,allowingtofurtherconstraintheparameterspaceofvariousextensionsoftheStandardModel,includingitssupersymmetricextensions.[120][121]

On13December2011,CERNreportedthattheStandardModelHiggsboson,ifitexists,ismostlikelytohaveamassconstrainedtotherange115130GeV.BoththeCMSandATLASdetectorshavealsoshownintensitypeaksinthe124125GeVrange,consistentwitheitherbackgroundnoiseortheobservationoftheHiggsboson.[122]

On22December2011,itwasreportedthatanewparticlehadbeenobserved,theb(3P)bottomonium

state.[103]

On4July2012,boththeCMSandATLASteamsannouncedthediscoveryofabosoninthemassregionaround125126GeV,withastatisticalsignificanceatthelevelof5sigma.ThismeetstheformallevelrequiredtoannounceanewparticlewhichisconsistentwiththeHiggsboson,butscientistswerecautiousastowhetheritisformallyidentifiedasactuallybeingtheHiggsboson,pendingfurtheranalysis.[123]

On8November2012,theLHCbteamreportedonanexperimentseenasa"golden"testofsupersymmetrytheoriesinphysics,[106]bymeasuringtheveryraredecayoftheBsmesonintotwo

muons(Bs0+).Theresults,whichmatchthosepredictedbythenonsupersymmetricalStandardModelratherthanthepredictionsofmanybranchesofsupersymmetry,showthedecaysarelesscommonthansomeformsofsupersymmetrypredict,thoughcouldstillmatchthepredictionsofotherversionsofsupersymmetrytheory.Theresultsasinitiallydraftedarestatedtobeshortofproofbutatarelativelyhigh3.5sigmalevelofsignificance.[124]TheresultwaslaterconfirmedbytheCMScollaboration.[125]

InAugust2013theLHCbteamrevealedananomalyintheangulardistributionofBmesondecayproductswhichcouldnotbepredictedbytheStandardModelthisanomalyhadastatisticalcertaintyof4.5sigma,justshortofthe5sigmaneededtobeofficiallyrecognizedasadiscovery.Itisunknownwhatthecauseofthisanomalywouldbe,althoughtheZ'bosonhasbeensuggestedasapossiblecandidate.[126]

On19November2014,theLHCbexperimentannouncedthediscoveryoftwonewheavysubatomicparticles,

band

b .Bothofthemarebaryonsthatarecomposedofonebottom,onedown,andone

strangequark.TheyareexcitedstatesofthebottomXibaryon.[127][128]

On13July2015,theLHCbcollaborationatCERNreportedresultsconsistentwithpentaquarkstatesinthedecayofbottomLambdabaryons(

0b).

[129][130][131]Theresultshavenotyetundergonepeerreview.

Secondrun(2015onward)

AttheconferenceEPSHEP2015inJuly,thecollaborationspresentedfirstcrosssectionmeasurementsofseveralparticlesatthehighercollisionenergy.

Planned"highluminosity"upgrade

Aftersomeyearsofrunning,anyparticlephysicsexperimenttypicallybeginstosufferfromdiminishingreturns:asthekeyresultsreachablebythedevicebegintobecompleted,lateryearsofoperationdiscoverproportionatelylessthanearlieryears.Acommonoutcomeistoupgradethedevicesinvolved,typicallyinenergy,inluminosity,orintermsofimproveddetectors.Aswellastheplanned20132015increasetoitsintended14TeVcollisionenergy,aluminosityupgradeoftheLHC,calledtheHighLuminosityLHC,hasalsobeenproposed,[132]tobemadein2022.

TheoptimalpathfortheLHCluminosityupgradeincludesanincreaseinthebeamcurrent(i.e.thenumberofparticlesinthebeams)andthemodificationofthetwohighluminosityinteractionregions,ATLASandCMS.Toachievetheseincreases,theenergyofthebeamsatthepointthattheyareinjectedintothe(Super)LHCshouldalsobeincreasedto1TeV.Thiswillrequireanupgradeofthefullpreinjectorsystem,theneededchangesintheSuperProtonSynchrotronbeingthemostexpensive.CurrentlythecollaborativeresearcheffortofLHCAcceleratorResearchProgram,LARP,isconductingresearchintohowtoachievethesegoals.[133]

Safetyofparticlecollisions

TheexperimentsattheLargeHadronCollidersparkedfearsthattheparticlecollisionsmightproducedoomsdayphenomena,involvingtheproductionofstablemicroscopicblackholesorthecreationofhypotheticalparticlescalledstrangelets.[134]TwoCERNcommissionedsafetyreviewsexaminedtheseconcernsandconcludedthattheexperimentsattheLHCpresentnodangerandthatthereisnoreasonforconcern,[135][136][137]aconclusionexpresslyendorsedbytheAmericanPhysicalSociety.[138]

ThereportsalsonotedthatthephysicalconditionsandcollisioneventswhichexistintheLHCandsimilarexperimentsoccurnaturallyandroutinelyintheuniversewithouthazardousconsequences,[136]includingultrahighenergycosmicraysobservedtoimpactEarthwithenergiesfarhigherthanthoseinanymanmadecollider.

Popularculture

TheLargeHadronCollidergainedaconsiderableamountofattentionfromoutsidethescientificcommunityanditsprogressisfollowedbymostpopularsciencemedia.TheLHChasalsoinspiredworksoffictionincludingnovels,TVseries,videogamesandfilms.

ThenovelAngels&Demons,byDanBrown,involvesantimattercreatedattheLHCtobeusedinaweaponagainsttheVatican.InresponseCERNpublisheda"FactorFiction?"pagediscussingtheaccuracyofthebook'sportrayaloftheLHC,CERN,andparticlephysicsingeneral.[139]Themovie

versionofthebookhasfootagefilmedonsiteatoneoftheexperimentsattheLHCthedirector,RonHoward,metwithCERNexpertsinanefforttomakethescienceinthestorymoreaccurate.[140]

ThenovelFlashForward,byRobertJ.Sawyer,involvesthesearchfortheHiggsbosonattheLHC.CERNpublisheda"ScienceandFiction"pageinterviewingSawyerandphysicistsaboutthebookandtheTVseriesbasedonit.[141]

Theshortstory"Breakthrough"byTomMorrisconsiderspossibleunexpectedandalarmingconsequencesoftheLHCexperiments.Availableonline(https://www.smashwords.com/books/view/155019)

CERNemployeeKatherineMcAlpine's"LargeHadronRap"[142]surpassed7millionYouTubeviews.[143][144]ThebandLesHorriblesCernetteswasfoundedbywomenfromCERN.ThenamewaschosensotohavethesameinitialsastheLHC.[145][146]

NationalGeographicChannel'sWorld'sToughestFixes,Season2(2010),Episode6"AtomSmasher"featuresthereplacementofthelastsuperconductingmagnetsectionintherepairofthesupercolliderafterthe2008quenchincident.Theepisodeincludesactualfootagefromtherepairfacilitytotheinsideofthesupercollider,andexplanationsofthefunction,engineering,andpurposeoftheLHC.[147]

TheLargeHadronColliderwasthefocusofthe2012studentfilmDecay,withthemoviebeingfilmedonlocationinCERN'smaintenancetunnels.[148]

ThefeaturedocumentaryParticleFeverfollowstheexperimentalphysicistsatCERNwhoruntheexperiments,aswellasthetheoreticalphysicistswhoattempttoprovideaconceptualframeworkfortheLHC'sresults.ItwontheSheffieldInternationalDoc/Festin2013.

OnionNewsNetworkfeaturedaparodiednewsstoryabouttheLHCtitled"BoredScientistsNowJustStickingRandomThingsIntoLargeHadronCollider".[149]

Seealso

CompactLinearColliderHighLuminosityLargeHadronColliderInternationalLinearColliderListofacceleratorsinparticlephysicsParticleFeverVeryLargeHadronCollider

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EightThingsToKnowAsTheLargeHadronColliderBreaksEnergyRecords(http://www.forbes.com/sites/chadorzel/2015/05/21/thingstoknowasthelargehadroncolliderbreaksenergyrecords/)

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