Presentation on theme: "Experimental Particle Physics PHYS6011 Joel Goldstein, RAL"— Presentation transcript:
1 Experimental Particle Physics PHYS6011 Joel Goldstein, RAL Introduction & AcceleratorsParticle Interactions and Detectors (2)Collider ExperimentsData Analysis
2 Administrative Points Three lectures now, two at end of termNotes for first part on webA couple of typos in Table 1Let me know if you find more!Will update notesAccompanying problem setReady on Monday
3 Introduction Heisenberg, de Broglie, Boltzmann, Big Bang: High momentum small distance high temperature early universeNeed sources of high energy particles and techniques to examine their interactionsNatural units are natural for some calculationsNot so natural for others: try ordering 5×109 GeV-1 thick aluminium!Use whichever units are most convenient (cm, M$, mb….)Know how to convertUse common sense
4 Useful Values In natural units Proton mass 1 GeV/c2 1 amu energy and momentum are measured in GeVlength and time are measured in GeV-11 = 197 MeV.fmProton mass 1 GeV/c2 1 amuFine structure constant 1/137Speed of light 1 foot per nanosecond
5 Natural Radioactivity First discovered in late 1800sUsed as particle source in many significant experimentsRutherford’s 1906 experiment: elastic scattering α+N α+NRutherford’s 1917 experiment: inelastic scattering α+N p+XCommon radioisotopes include55Fe: 6 keV 90Sr: 500 keV 241Am: 5.5 MeV αEasy to control, predictable flux but low energyStill used for calibrations and tests
6 Cosmic Rays Low energy cosmic rays from Sun Solar wind (mainly protons)NeutrinosHigh energy particles from sun, galaxy and perhaps beyondNeutrinos pass through atmosphere and earthLow energy charged particles trapped in Van Allen BeltHigh energy interact in atmosphereFlux at ground level mainly muons: s-1 m-2Highest energy ever seen ~1020eV
7 Cosmic ExperimentsPrimary source for particle physics experiments for decadesDetectors taken to altitude for larger flux/higher energyPositron and many other particles first observedModern experiments include:Particle astrophysicsSpace, atmosphere, surface, undergroundNeutrinoSolar, atmospheric“Dark Matter” searchesStill useful for calibration and testing
8 Reactor Experiments Huge fluxes of MeV neutrons and electron neutrinos First direct neutrino observationNew results on neutrino oscillations
9 Particle Sources +ve -ve Want intense monochromatic beams on demand: Make some particlesElectrons: metal + few eV of thermal energyProtons/nuclei: completely ionise gasAccelerate them in the labHydrogen gas bottleVe--ve+veK.E. = e×V
10 Cockroft and Walton’s Original Design Fermilab’s 750kV Cockroft-Walton DC AcceleratorsVan de Graaff at MITCockroft and Walton’s Original DesignFermilab’s 750kV Cockroft-Walton
11 Cyclotrons DC accelerators quickly become impractical Air breaks down at ~1MV/mUtilise motion in magnetic field: p = kqBRApply AC to two halvesLawrence achieved MeV particles with 28cm diameterMagnet size scales with momentum…Still used for medical purposes
12 Linear Accelerators For energies greater than few MeV: use multiple stagesRF easier to generate and handleBunches travel through resonant cavitiesSpacing and/or frequency changes with velocityCan achieve 10MV/m and higher3km long Stanford Linac reached 45 GeV
14 Synchrotrons p = kqBR Cyclotron has constant B, increasing R Increase B keeping R constant:variable current electromagnetsparticles can travel in small diameter vacuum pipesingle cavity can accelerate particles each turnefficient use of space and equipmentDiscrete components in ringcavitiesdipoles (bending)quadrupoles etc. (focusing)diagnosticscontrol
15 A Real Synchrotron LEAR – a particle decelerator and storage ring Why aren’t all accelerators synchrotrons?
16 Synchrotron Radiation Accelerated charges radiateAverage power loss per particle:Quantum process → spread in energyFor a given energy ~ 1/mass4Electron losses times protonHigh energy electon machines have very large or infinite RPulsed, intense X-ray source may be useful for some things....
17 Fixed Target Experiments Beam incident on stationary targetInteraction products have large momentum in forward directionLarge “wasted” energy small sIntense beams/large target high rateSecondary beams can be made
18 Neutrino Beams Fermilab sends a muon-neutrino beam to Minnesota p beamPion beamFermilab sends a muon-neutrino beam to MinnesotaLooking for oscillationsDetector at bottom of mine shaft
19 Antiparticle Production Positrons and antiprotons produced in fixed target collisionstypical efficiency 105 protons per antiprotonLarge phase space – must be “cooled”synchrotron radiation damps electronsantiproton cooling techniques won Nobel (see LEAR photo)Decelerated and accumulated in storage rings
20 Colliders Incoming momenta cancel s = 2Ebeam Same magnetic field deflects opposite charges in opposite directions Antiparticle accelerator for free!particle/antiparticle quantum numbers also cancelTechnically challengingLuminosityInteraction rate =
21 Different Colliders p pbar e+ e- e p p p ion ion + - energy frontierdifficult to interpretlimited by pbar productionSPS, Tevatrone+ e-relatively easy analysishigh energies difficultLEP, PEP...e pproton structureHERAp phigh luminosityenergy frontierLHCion ionquark gluon plasmaRHIC, LHC+ -some plans exist !!!
22 Full details at pdg.lbl.gov Collider ParametersFull details at pdg.lbl.gov
23 Inside the Tunnels Underground for shielding and stability Focusing MagnetConcrete Dipole
24 Complexes Synchrotrons can’t accelerate particles from rest Designed for specific energy range, normally about factor of 10accelerators are linked into complexes
25 Charged particle interactions and detectors Next Time...Charged particle interactions and detectors
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