Atom Smashers Particle Accelerators and Detectors Mats Selen
- Slides: 44
Atom Smashers Particle Accelerators and Detectors Mats Selen, UIUC l What’s the motivation ? l How to build a particle accelerator. l How to build a particle detector. A great web site with lots of links is: http: //pdg. lbl. gov/particleadventure/english/index. html Saturday Physics, 12/4/99
What’s the Motivation ? l Try to make sense of the way the Universe works çLook for simple explanations to complicated looking observations ! Complication Simplification There is lots of different “stuff” on earth There are many different kinds of atoms There are lots of elements We can make “other” stuff (not made of protons neutrons and electrons) We don’t really understand this at a fundamental level (Standard Model has too many free parameters) Small indivisible “Atoms” Elements (Periodic Table) Nucleus (protons, neutrons) and electrons Everything made out of quarks & leptons Smash More Atoms ! Saturday Physics, 12/4/99
How to build a Particle Accelerator First get some particles: ee e eeee ee e e eee Electrons are easy: Just heat up a filament + ENERGIZER e e + + + e e + + Protons are also quite easy: Ionize hydrogen e - ENERGIZER Saturday Physics, 12/4/99
Now Accelerate Them We’d like to give them lots of kinetic energy (lets say 10 Ge. V) | + Van. De. Graaff Accelerator + 10, 000, 000 volt battery + + ENERGIZER + + ++ + Do Vd. G & bubble demo This can’t provide enough energy (only a few million volts) ! Need bigger voltage (and a vacuum system) !! Saturday Physics, 12/4/99
Linear Accelerator | +| +| + + + ENERGIZER ENERGIZER Saturday Physics, 12/4/99
Linear Accelerator - + + + - + ENERGIZER - Saturday Physics, 12/4/99
Linear Accelerator - + + + ENERGIZER - Saturday Physics, 12/4/99
Linear Accelerator - + + + - + ENERGIZER - Saturday Physics, 12/4/99
Linear Accelerator - + + + ENERGIZER - Saturday Physics, 12/4/99
Linear Accelerator - + + + - + ENERGIZER - Saturday Physics, 12/4/99
Linear Accelerator - + + + - + RF - Saturday Physics, 12/4/99
Some Examples LINAC at Bates Lab (MIT) (0. 5 Ge. V) LINAC at Fermilab (0. 4 Ge. V) Saturday Physics, 12/4/99
A Bigger Example SLAC (Stanford) (50 Ge. V) Saturday Physics, 12/4/99
But some people like to recycle. . . l Have the particles go through the same accelerator cavity many times Circular “track” (high-vacuum beam-pipe) This is called a Synchrotron Small linear accelerator Key ingredients: + Need to make particles go in a circle Need to keep everything synchronized Saturday Physics, 12/4/99
Forces on Charged Particles l Both electric and magnetic fields influence the motion of charges. Magnetic field “north” points into screen X X X | + E + q X F F = q. E X X X X F X X v X F X X + ENERGIZER X X q X X X + X q. X X X F = qv x B v X ENERGIZER X X X E/m demo TV demo Geiger demo Saturday Physics, 12/4/99
Synchrotrons bending magnet Accelerating section Focussing magnets Vacuum tube (beam pipe) Saturday Physics, 12/4/99
Fermilab Booster (8 Ge. V) Main Ring (150 Ge. V) Tevatron (1000 Ge. V) Saturday Physics, 12/4/99
A slick trick Two for the price of one 2000 Ge. V 1000 Ge. V + - 1000 Ge. V Saturday Physics, 12/4/99
CERN NOW LEP 200 Ge. V e+ e- In 5 -6 years LHC 14000 Ge. V p p Saturday Physics, 12/4/99
LEP Tunnel Saturday Physics, 12/4/99
How to build a Particle Detector Ideally, we want to measure everything (E, Px, Py, Px) about every particle produced in the “collision”. Charged Particles Neutral Particles + - Saturday Physics, 12/4/99
Most Common Approach (for colliding beam experiments) Detector “package” looks like a beer can + - Saturday Physics, 12/4/99
The Parts Vertex Detector to measure the position of charged particles close to their point of creation. Solenoid (Magnet) (Makes charged particles curve, which tells us their momentum) Drift Chamber to measure the path of charged particles. Low density…mostly gas…so particles don’t notice it much. Calorimeter to measure the energy of neutral particles. High density…particles often stop here. Saturday Physics, 12/4/99
How it works l l 1) All of the parts work more or less the same way: Charged particles ionize the material they pass through, and we can detect signs of this ionization. + e- + em+ edetect electron Geiger counter Saturday Physics, 12/4/99
How it works l l 2) All of the parts work more or less the same way: Charged particles ionize the material they pass through, and we can detect signs of this ionization. + e- + scintillation e- m+ detect photon Scintillator counter Saturday Physics, 12/4/99
Lets Try It l We don’t have an accelerator handy so lets look at cosmic rays: p m Cloud chamber Saturday Physics, 12/4/99
Scintillation Detector l l Photons are produced in the plastic by scintillating molecules when a cosmic ray muon whizzes through it. These photons are detected by a photo-multiplier tube, and result in pulses on the oscilloscope. Wrapped scintillator oscilloscope Photo-multiplier Singles coincidence beta Saturday Physics, 12/4/99
Concluding Remarks l l The pursuit of High Energy Physics is motivated by a quest for fundamental understanding. Current accelerator and detector technology is very cool. Saturday Physics, 12/4/99
The Periodic Table Saturday Physics, 12/4/99
The Periodic Table Explained ? Look carefully proton neutron electron Saturday Physics, 12/4/99
The nucleus is much smaller than the atom This is about 500 times too big Even so, the nucleus contains > 99. 9 % of the mass of the atom ! Saturday Physics, 12/4/99
Energy vs Mass He (m=4. 0026 u) O (M=15. 9995 u) 4 x He = 16. 01 u Mass difference = 0. 01 u = binding energy So energy is the same as mass somehow ? ? sure E = mc 2 Units Saturday Physics, 12/4/99
Mass from Energy KE 1 KE 2 Saturday Physics, 12/4/99
Mass from Energy Ebefore = Eafter Mostly KE New Mass + KE Saturday Physics, 12/4/99
Units E = mc 2 E=m Physicists are sloppy 1 e. V = kinetic energy of an electron accelerated through a 1 volt potential difference This is a small amount of energy (more appropriate for chemistry) - e- + ENERGIZER Preferred unit of Energy/Mass = Ge. V 1 volt battery 1 Ge. V = 109 e. V (a billion e. V) (about the mass of a proton…appropriate scale for us) Saturday Physics, 12/4/99
It gets more complicated again. . . p 2 K* p a 1 K 1 a 2 h f 4 a 4 D* W K Lc D*2 f 3 B S r D 2 D 1 K*2 K*3 w K*4 w f’ 2 f 0 w 3 L B* D f 2 Sc K 3 h 1 a 0 Bc K 2 fj h 0 Ds f 1 Bs f h’ r 3 Saturday Physics, 12/4/99
quarks + 2/3 - 1 /3 up down quark charge charm strange & top bottom leptons -1 0 e m t ne nm nt lepton charge Saturday Physics, 12/4/99
quarks & anti-quarks + 2/3 - 1 /3 u d c s t b Now we can easily build any of of the particles we have discovered (and predict some we haven't) - 2/3 u c t d s b + 1 /3 (baryons) proton neutron anti-proton (mesons) p+ D 0 Bs Saturday Physics, 12/4/99
Example: CLEO Saturday Physics, 12/4/99
Example: L 3 =2 X Saturday Physics, 12/4/99
Vertex Detector (CLEO) Saturday Physics, 12/4/99
Drift Chamber Saturday Physics, 12/4/99
Calorimeter Saturday Physics, 12/4/99
Solenoid Saturday Physics, 12/4/99