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Saturday Physics, 12/4/99 Atom Smashers Particle Accelerators and Detectors Atom Smashers Particle Accelerators and Detectors Mats Selen, UIUC l What’s.

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Presentation on theme: "Saturday Physics, 12/4/99 Atom Smashers Particle Accelerators and Detectors Atom Smashers Particle Accelerators and Detectors Mats Selen, UIUC l What’s."— Presentation transcript:

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2 Saturday Physics, 12/4/99 Atom Smashers Particle Accelerators and Detectors 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

3 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 There is lots of different “stuff” on earth Simplification Small indivisible “Atoms” There are many different kinds of atoms Elements (Periodic Table) There are lots of elements Nucleus (protons, neutrons) and electrons We can make “other” stuff (not made of protons neutrons and electrons) Everything made out of quarks & leptons We don’t really understand this at a fundamental level (Standard Model has too many free parameters) Smash More Atoms !

4 Saturday Physics, 12/4/99 How to build a Particle Accelerator First get some particles: Electrons are easy: Just heat up a filament e e e e e e e e e e e e e e e e Protons are also quite easy: Ionize hydrogen + e + e + e + e + e + e + e + e ENERGIZER - + + -

5 Saturday Physics, 12/4/99 Now Accelerate Them + | ENERGIZER 10,000,000,000 volt battery + We’d like to give them lots of kinetic energy (lets say 10 GeV) This can’t provide enough energy (only a few million volts) ! Need bigger voltage (and a vacuum system) !! Do VdG & bubble demo VanDeGraaff Accelerator + + + + + + + + + + + + + + + + + +

6 Saturday Physics, 12/4/99 Linear Accelerator + | ENERGIZER + + | + + | + + | + + | +

7 Saturday Physics, 12/4/99 Linear Accelerator ENERGIZER + - + + - + -

8 Saturday Physics, 12/4/99 Linear Accelerator ENERGIZER + - + - + - +

9 Saturday Physics, 12/4/99 Linear Accelerator ENERGIZER + - + + - + -

10 Saturday Physics, 12/4/99 Linear Accelerator ENERGIZER + - + - + - +

11 Saturday Physics, 12/4/99 Linear Accelerator ENERGIZER + - + + - + -

12 Saturday Physics, 12/4/99 Linear Accelerator + - + + - + - RF

13 Saturday Physics, 12/4/99 Some Examples LINAC at Fermilab (0.4 GeV) LINAC at Bates Lab (MIT) (0.5 GeV)

14 Saturday Physics, 12/4/99 A Bigger Example SLAC (Stanford) (50 GeV)

15 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 Need to make particles go in a circle Key ingredients: Need to keep everything synchronized Small linear accelerator

16 Saturday Physics, 12/4/99 Forces on Charged Particles l Both electric and magnetic fields influence the motion of charges. + | + E F = qE F q ENERGIZER XXXXXX XXXXX XXXXX XXXX XXXXX X XXX XXXX Magnetic field “north” points into screen F + q v + q F v F = qv x B E/m demo TV demo Geiger demo ENERGIZER

17 Saturday Physics, 12/4/99 Vacuum tube (beam pipe)Synchrotrons bending magnet Accelerating section Focussing magnets

18 Saturday Physics, 12/4/99 Booster (8 GeV) Main Ring (150 GeV) Tevatron (1000 GeV) Fermilab

19 Saturday Physics, 12/4/99 A slick trick Two for the price of one 1000 GeV - + 2000 GeV

20 Saturday Physics, 12/4/99 CERN LEP 200 GeV e + e - NOW LHC 14000 GeV p p In 5-6 years

21 Saturday Physics, 12/4/99 LEP Tunnel

22 Saturday Physics, 12/4/99 How to build a Particle Detector Ideally, we want to measure everything (E, P x, P y, P x ) about every particle produced in the “collision”. + - Charged Particles Neutral Particles

23 Saturday Physics, 12/4/99 Most Common Approach (for colliding beam experiments) Detector “package” looks like a beer can - +

24 Saturday Physics, 12/4/99 The Parts Solenoid (Magnet) (Makes charged particles curve, which tells us their momentum) Calorimeter to measure the energy of neutral particles. High density…particles often stop here. Vertex Detector to measure the position of charged particles close to their point of creation. Drift Chamber to measure the path of charged charged particles. Low density…mostly gas…so particles don’t notice it much.

25 Saturday Physics, 12/4/99 How it works l All of the parts work more or less the same way: l Charged particles ionize the material they pass through, and we can detect signs of this ionization. + e- detect electron + e- ++ 1) Geiger counter

26 Saturday Physics, 12/4/99 How it works l All of the parts work more or less the same way: l Charged particles ionize the material they pass through, and we can detect signs of this ionization. + e- + ++ detect photon 2) + e- scintillation Scintillator counter

27 Saturday Physics, 12/4/99 Lets Try It l We don’t have an accelerator handy so lets look at cosmic rays: p  Cloud chamber

28 Saturday Physics, 12/4/99 Scintillation Detector l Photons are produced in the plastic by scintillating molecules when a cosmic ray muon whizzes through it. l These photons are detected by a photo-multiplier tube, and result in pulses on the oscilloscope. Wrapped scintillator Photo-multiplier oscilloscope Singles coincidence beta

29 Saturday Physics, 12/4/99 Concluding Remarks l The pursuit of High Energy Physics is motivated by a quest for fundamental understanding. l Current accelerator and detector technology is very cool.

30 Saturday Physics, 12/4/99 The Periodic Table

31 Saturday Physics, 12/4/99 The Periodic Table Explained ? proton neutron electron Look carefully

32 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 !

33 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 ?? E = mc 2 sure Units

34 Saturday Physics, 12/4/99 Mass from Energy KE 1 KE 2

35 Saturday Physics, 12/4/99 Mass from Energy E before = E after Mostly KE New Mass + KE

36 Saturday Physics, 12/4/99Units E = mc 2 E = m Physicists are sloppy Preferred unit of Energy/Mass = GeV 1eV = kinetic energy of an electron accelerated through a 1 volt potential difference + - e-e- ENERGIZER 1 volt battery This is a small amount of energy (more appropriate for chemistry) 1GeV = 10 9 eV (a billion eV) (about the mass of a proton…appropriate scale for us)

37 Saturday Physics, 12/4/99 It gets more complicated again...     ’’ a0a0 f0f0   a1a1 h0h0 h1h1 f’ 2 f1f1 a2a2 f2f2   fjfj   a4a4 f4f4 K* K K1K1 K2K2 K* 2 K3K3 K* 3 K* 4 DsDs D1D1 D* 2 D* D D2D2 B* B BsBs BcBc cc  cc  

38 Saturday Physics, 12/4/99 quarks & leptons quark charge up down charm strange top bottom + 2 / 3 - 1 / 3 0 e   e   lepton charge

39 Saturday Physics, 12/4/99 quarks & anti-quarks proton neutron ++ D0D0 BsBs u d c s t b + 2 / 3 - 1 / 3 - 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) (baryons) (mesons) anti-proton

40 Saturday Physics, 12/4/99 Example: CLEO

41 Saturday Physics, 12/4/99 Example: L3 = 2 X

42 Saturday Physics, 12/4/99 Vertex Detector (CLEO)

43 Saturday Physics, 12/4/99 Drift Chamber

44 Saturday Physics, 12/4/99 Calorimeter

45 Solenoid

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