Introduction to Experimental Particle Physics : Lecture 1

Introduction to Experimental Particle Physics : Lecture 1

John Swain, Northeastern University, Boston

Graz, September 2012

Friday, September 14, 2012

Very, very, very important...

We’re just starting!...whole field is about 100 years old. See my

Santoro festschrift article...

Better a little less with more clarity or inspiration...please

don’t let me lose you!


Plan by Material(not necessarily by lecture!)• I Introduction, Motivation, Early History

• II Particles, sources, accelerators

• III Detectors I : “zero mass” (trackers)

• IV Detector II : “infinite mass” (calorimeters)

• V Triggers, computing, simulation, reconstruction, analysis, publication

• VI Outlook for the future


The Intellectual Content of Experimental Physics

• Victor Weisskpof, CERN Yellow Report

• Question:

• Why do so many of the brightest students want to do theory?

• Answer:

• 1) almost all courses are theoretical

• 2) almost all textbooks are theoretical


Constraints

This (not even all of it!) is all you get to work with...Friday, September 14, 2012

Actually, at the start we know much less...

Text

N.B.: Conceptions of “fundamental” change -- important to know that they are modes of thought

rather than intrinsic realities. (This isn’t “wrong”...these are phases of matter.)

http://www.glogster.com/mcrsavedmylife/earth-day/g-6n56c80ogh4oukhblvhnta0




Tools get better though...and we start to learn more...


Terrestrial Radioactivity• Antoine Henri Becquerel (15

December 1852 – 25 August 1908)

• Discovers radioactivity in phosphorescent uranium salts

• Nobel prize (with M. and P. Curie) in 1903

• By no means trivial -- Kelvin predicts age of earth to be 20-400 My


Rutherford’s alpha, beta, gamma rays (1898-1902)

http://library.thinkquest.org/28383/nowe_teksty/htmla/1_26a.html

http://www.gsseser.com/Quarterlies/helpful2.htm

Now: Helium nuclei, fast electrons (and e+!), photonsFriday, September 14, 2012









Rutherford scattering• 1911: Discovery

of the atomic nucleus in a scattering experiment

• prototype of most particle physics progress:

• source of particles

• collisions

• detection

• data collection

• analysishttp://www.wiredchemist.com/files/shared/images/figure8.gif


http://www.wiredchemist.com/files/shared/images/figure8.gif

http://www.wiredchemist.com/files/shared/images/figure8.gif

Really an extension of vision

Descartes Ipanema using natural photons of a few eV and photographic film/eye.

(http://questpointsolarsolutions.com/?p=1313)9

HEP: replace natural sources (often) and replace eye with detectors!Friday, September 14, 2012

http://questpointsolarsolutions.com/?p=13139

http://questpointsolarsolutions.com/?p=13139

In anticipation of later...

• You only see what you look for.

• Post-processing (human brain always, perhaps other things too!) influence what’s selected

• Even after selection, you can still miss things! (Basketball plus gorilla experiment)


Discovery of the Neutron

• Chadwick (1932)

• Essentially same idea as Rutherford experiment

http://www.kutl.kyushu-u.ac.jp/seminar/MicroWorld3_E/3Part1_E/3P13_E/DiscoverNeutron_E.htm






Radiation from Space• Victor Francis Hess(24

June 1883 – 17 Dec 1964)

• Discovers radioactivity increasing with altitude

• Nobel prize in 1936

• Again, by no means trivial

• Led to a vast array of discoveries in particle physics and astrophysics and is still doing so!


Hess’s Great Work

• 1911-1913 discovers radioactivity increasing with altitude above 1km

• some evidence before, but Hess flies vastly improved electroscopes (!) in balloons up to 5.3 km...and does it himself! (and at great personal risk)

• free natural (uncontrolled) accelerator, very primitive detector


Feynman and Einstein• If, in some cataclysm, all of scientific knowledge were to be

destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis that

All things are made of atoms-little particles that that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.

In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied.

1906: Einstein’s “annus mirabilis”: photoelectric effect and Brownian motion


Particles Discovered via Cosmic Rays 1: The Positron

• Cloud chamber with magnetic field

• Curvature less at top means comes up

• Must be positive

• dE/dx means can’t be proton

• First time a predicted (Dirac 1928) particle is discovered!!C.D. Anderson, Physical Review 43, 491 (1933)


The mu and pi mesons & more...

• The muon: 1937 by J. C. Street and E. C. Stevenson: "New Evidence for the Existence of a Particle Intermediate Between the Proton and Electron", Phys. Rev. 52, 1003 (1937) in a cloud chamber

• The pion: 1947 by Cecil Powell, César Lattes, Giuseppe Occhialini et al. in Bristol, England in emulsion; predicted by Yukawa in 1935 (Nobel in 19490); another Nobel to Powell in 1950

• later Lamda, Xi and Sigma all found in cosmic ray interactions


http://en.wikipedia.org/wiki/Cecil_Powell

http://en.wikipedia.org/wiki/Cecil_Powell

http://en.wikipedia.org/wiki/C%C3%A9sar_Lattes

http://en.wikipedia.org/wiki/C%C3%A9sar_Lattes

http://en.wikipedia.org/wiki/Giuseppe_Occhialini

http://en.wikipedia.org/wiki/Giuseppe_Occhialini

What sorts of particles do we know?

• photons

• electrons, muons (“who ordered that?”)

• protons, neutrons, nuclei

• pions, kaons

• neutrinos

• understood from representation of the

Poincare group: (mass, spin)Friday, September 14, 2012

What is a particle?• The key modern idea - invariances under

rotations, boosts, and translations

Interesting non-invariance under a scale change...

Question: Is special relativity trivial for you? This is not a trick question -- please be honest!


Nontrivial Scale Transformations in QFT

Obvious absolute scale not present in Maxwell theory provided by particle masses..but it’s not as simple as “no

scale invariance”.Friday, September 14, 2012

Particles and Forces

•The Periodic Table in 2012Friday, September 14, 2012

A feeling for energies

• Room temperatare kT ~ 1/40 eV

• Flashlight battery ~1.5 eV

• Visible light ~ a few eV

• UV - ionization of hydrogen at 13.6 eV

• X-rays - keV

• Nuclear - MeV

• Inside a proton - GeV


Why accelerate?

• nature gives us radioactive decays: keV to MeV, but we want more, More, MORE!!!

• high energies as a microscope (colliding Swiss watches to see what’s inside!)

• high energies as a window back in time

• QFT: create new particles (!)

• Not just Poincare transformations -- things change under scale transformations too!


Virtual Processes• Everything happens

when you’re not looking (2-slit experiment)

• Uncertainty principle as an alternative to going to higher energies

• Simple example: muon decay

• Rare decays, precision g-2, etc.


4 Forces we could use for acceleration

• Need to apply a FORCE through a DISTANCE

• Electromagnetism -- good candidate!

• Gravity -- too weak

• Weak -- too short range and too weak

• Strong -- too short range


What we can accelerate?...

• Nuclei and protons

• have structure which even changes with scale

• collisions are dirty

• Electrons

• “pointlike”, but still have structure due to QFT

• Bremsstrahlung: Prob ~ square of mass


Fixed target vs. collisions

• All energy available to make particles only in collider

• Q: Is this easy for you to see? To work out?

http://hep.physics.indiana.edu/~hgevans/classes/graphics/detectors/types/fix_coll.html

This is not a trick question -- please be honest!Friday, September 14, 2012



Introduction to Experimental Particle Physics : Lecture 1

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