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Lecture 9 PARTICLE DETECTORS

Lecture 9 PARTICLE DETECTORS. Detlev Gotta Institut für Kernphysik, Forschungszentrum Jülich / Universität zu Köln GGSWBS'12 , Batumi, Georgia 5th Georgian – German School and Workshop in Basic Science August 16, 2012 . WHAT TO DETECT ?. EXAMPLES OF COMBINED DETECTION SYSTEMS.

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Lecture 9 PARTICLE DETECTORS

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  1. Lecture 9 PARTICLE DETECTORS Detlev Gotta Institut für Kernphysik, Forschungszentrum Jülich / Universität zu Köln GGSWBS'12, Batumi, Georgia 5th Georgian – German School and Workshop in Basic Science August 16, 2012

  2. WHAT TO DETECT ? EXAMPLES OF COMBINED DETECTION SYSTEMS HOW TO DETECT? INTERACTION OF CHARGED PARTICLES WITH MATTER“ MASSIVE NEUTRAL PARTICLES WITH MATTER “ RADIATION WITH MATTER DETECTOR PRINCIPLES

  3. WHAT TO DETECT ?

  4. PARTICLES particledetectorregistration Light Heavy

  5. PARTICLES Whatcharacterizes a particle? mass M charge Q Spin intrinsic angular momentum S life time t0 shape (forextendedparticles) <r2>

  6. RADIATION fluid gas „light“ fundamental constant: c = speedof light in vacuum ( 30 cm / ns)

  7. RADIATION Whatcharacterizeswaves? wavepropagationvelocity c = ln wavelengthl frequencyn particlephysics usuallyelectromagneticradiation wavepropagationvelocity in vacuum c = l n “ “ “ in medium c‘ = l‘n < c indexofrefaction n = c / c‘

  8. CONSTITUENTS OF MATTER I atoms atomicshellsnucleus electronprotonneutron e p n Q  1 + 1 0 MMp / 1836 Mp Mp size < 10-18 m 0.8  10-15m life time t0 > 1026 y > 1029 y 886 s decay - - n  p en 10-10m

  9. CONSTITUENTS OF MATTER II newparticles – unstablebeingfree • pionskaonsmanymore • p K … • Q 0,  1 2  0,  1 • M Mp / 7  Mp / 2 • size 0.6  10-15 m 0.6  10-15 m • life time t0p 2610-9 s K 1210-9 s • p0 810-17sK0S,L910-10 / 510-8 s • decayp m  n K m n, … • p0 g g K0 p + p- , p0 p0 ,...

  10. PARAMETERS massive particlesel.-mag. radiation total energy restmass m0≠ 0 rangein matter = 0 attenuation in matter charge Q ≠ 0 deflection in el.-mag fields = 0 nodeflection life time  = 0decaylengthl = v t =  relativisticfactor h Planck constant = minimal action

  11. HOW TO DETECT ?

  12. FORCES • nuclearforcekeepsprotonsandneutronstogether • electromagneticforcekeepselectronsaroundthenuclei • weakforcemakesthe (free) neutrontodecay • gravitationkeepsus on theground Standard Model strength

  13. ELECTROMAGNETIC FORCE • a forceismediated • classicalpicturequantumworld • byfieldaround a sourcefieldquanta = particles • „light“ particles = photonsg electromagneticradiation = E and B fieldsinteractswithelectriccharges

  14. DEFLECTION OF CHARGED PARTICLES IN EL.-MAG. FIELDS • electricfield • magneticfield B = const.  circularmotion B  plane ofprojection r

  15. SIGNAL CREATION • via electriccharges • measuretheelectriccurrentIorvoltageU Q I resistor R U U capacitor C

  16. INTERACTION OFCHARGED PARTICLES WITH MATTER

  17. CHARGED PARTICLES interactionhappensbycollisionsofparticles type 1 and 2 • before after collision • 1. Mparticle 1 >> Mparticle 2 • 2. Mparticle 1 = Mparticle 2

  18. CHARGED PARTICLES I: ENERY LOSS BY COLLISIONS collisionscreateelectronionpairs Bragg peak 1. Mparticle >> Melectron e.g. protons, deuterons, … 2. Mparticle= Melectron electronsorpositrons for all elements stronglyionising welldefinedrange R! nodefinedrange R! exponentialattenuationwithdepth x µ: material dependentattenuationcoefficient weaklyionising

  19. CHARGED PARTICLES II: ENERY LOSS BY RADIATION Radiation ifvparticle > cin medium Cerenkov 1930s „light“ blue! thechargepolarizesthe medium emissionunderspecific angle C electrons „radiate“ in thewaterabove thecoreof a nuclear power plant cos C = 1 / n n = indexofrefraction (small) dispersion ! Cmeasuresthevelocityoftheparticle Cerenkov wave front acousticsanalogue: Mach‘s coneforsupersonicsource

  20. INTERACTION OFMASSIVE NEUTRAL PARTICLES WITH MATTER

  21. NEUTRONS collisionscreaterecoilparticles maximumenergytransferforMneutral = Mrecoil centralcollision all energyistransferred non central all energiesaccordingtoscattering angle cloudchamberpicture neutrons– nodefinedrange detectionbyrecoilofprotons (from hydrogen) MProtonMNeutron i.e. goodshieldingsarewater concrete (15% water) paraffin ( (CH)n) … energytransferDE per collision probability DE neutrons

  22. INTERACTION OFRADIATION WITH MATTER

  23. RADIATION I : PHOTO EFFECT requiresparticlenatureof „light“ Einstein 1905 1. photondisappears photoelectronEe = Ephoton- EB 2. refillingof hole in electronshellby a) emissionofphotonor b) Augerelectronemissionof looselyboundouterelectron EAuger EB detectedenergy E photopeak E = Ephoton = Ee+ EB escapepeak E = Ephoton - EKa photo peak escape peak example Argon EKa = 2.95 keV photonEPhoton = 6.41 keV Energy

  24. RADIATION II : COMPTON EFFECT proofofparticlenatureof „light“ Compton 1922 billardwithphotonsand „quasifree“ electrons Δλ =λ (1− cosθ ) photondoesnotdisappear recoilelectronEe = Ephoton– Ephoton‘  continuousspectrum detectedenergyE = Ee weneglegt EBoftheelectron andErecoilofthenucleus becauseusually EB, Erecoil<< Ee Compton edge = maximumenergytransfer

  25. RADIATION III : BREMSSTRAHLUNG acceleratedchargedparticlesradiate Hertz 1886 electromagneticwaves bendingforceby Coulomb potential force acceleration anydistance r  continuousspectrum a recoilpartner (nucleus) isneededtofulfil energyandmomentumconservation characteristic X-rays refillingofholes in inneratomicshells

  26. +Ze RADIATION IV : PAIR PRODUCTION proofofmass-energyequivalence Blackett 1948 conversionofenergyinto matter Ephoton = h> 2 melectron in general > 2 mparticlesat very high energies el.-mag shower e+ e –  - cascade pair productionand Bremsstrahlung alternate shower may start with photon orelectron radiation length x0 characteristic material dependent constant depth, where about 2/3 of the incident energy is converted a recoilpartner (nucleus) isneededtofulfil energyandmomentumconservation  magneticfieldB

  27. CHARGED PARTICLES : SUMMARY I  2M0 MIPs minimumionsingparticles • stoppingpower T < 2M0 Fractional energy loss.

  28. CHARGED PARTICLES : SUMMARY II Fractional energy loss per radiation length in lead as a function of electron or positron energy.

  29. RADIATION: SUMMARY I crosssections  Z5 s reactionprobability

  30. x Io I dx RADIATION: SUMMARY II Lambert-Beer law attenuation intensity after layerthickness x transmission sumof linear attanuationcoeff.

  31. DETECTOR PRINCIPLES

  32. not only HISTORY (Wilson) cloudchamber typical Open Day presentations saturatedalcoholvapor  a-particleemittingnuclide overheatedLH2 bubblechamber (D. Glaser noble prize 1960) + magneticfield "beer" inspired!!! amongothers discoveryofthe weak neutral current BEBC @ CERN 73 until 80ies 3.7 T, 35 m3 LH2

  33. CHARGE capacitor voltagegenerator ionisingparticle currentorvoltagedetection chargecreatedbychargedparticlesorby„light“iscollected byapplying a voltagebymeansof a curentorvoltagedetection

  34. SCINTILLATORS produce “LIGHT” ionisationcausedby chargedparticlesorlight excitationanddelayed light emission usually in the UV range anorganicNaI(Tl), CSI, BaF2, … inorganicdoped „plastics“ UV light isconvertedtocharge at a photocathodeand multipliedby a multistage photo „multiplier“ 

  35. TIME 10 ns

  36. WIRE CHAMBERS I electronmultiplication aroundanode (fast) driftofions (slow) typicaliondriftvelocity: 1 - 10 cm/(µskV) Ar CH4 multiplication avalanche gain 105 - 106 to control avalanche quench gases, e.g. CO2, CH4, C2H6 wirechamberstutorial: F. Sauli CERN yellowreport 99-07

  37. WIRE CHAMBERS II manywires: MWPC = multiwire proportional chamber positionresolution wiredistancetypically 2 mm fieldconfiguration • (x,y) - coordinate per pair offrames • trajectoryfrom MWPC stacks

  38. WIRE CHAMBERS III tracking: cut on fiducialtargetvolume example: p-3He pnnordn target 3He vesssel pion beam protons MWPC 1 beam defining counters beam definingcounters mainlypcarbonreactions deuterons MWPC 2 goodbadevent

  39. Type-2 module (520 ‘straws’) ATLAS at the LHC Ileft Iright Dz < 1 mm z ZEUS - DESY wedge STRAW TUBES individual counters, timing 20 ns HV: coat, ground: sense wire (~ kV) typicalsize: length 1 - 2 m, f mm - cm "simple" mechanics 10 MHz rate inside magnetic field gas filling e.g., Ar/C2H6 Monte Carlo simulation resistive read out wall: aluminised mylar foils anode wire: f 20 µm

  40. DRIFT CHAMBERS I time  position external time reference, e.g., plastic scintillator trick: choose field configuration, which keeps the nonlinearity of time-to-position relation small position resolution 20 µm

  41. inclined wires DRIFT CHAMBERS II improved position resolution by nearest 3 wires method

  42. STAR TPC - RHIC, Brookhaven TPC - time projectionchamberDavid Nygren, 1974 idea: avoid pile-up many MWPC planes (typical gas thickness of 1 cm) principle: electrons produced follow the constant electric field lines to a single MPWC plane located at one end of the volume ( x-y coordinates on this plane) Third coordinate, z, from the drift time of the electrons to the anode plane • properties: • full 3-dimensional detector • constant drift velocity due to the collisions in the gas mixture (typical a few cm/µs). • low occupancy even for high background (high rates) • large dE/dx due to large gas thickness (particle identification)

  43. Charge Sharing Track Cluster • Pixel Tracker • Pixel Size • Occupancy • Charge Sharing • S/N • ExB Drift • Radiation Damage • LHC - 1014 /cm2/yr Single Track & Trigger charge center of gravity  high position resolution vertex resolution (20-30) mm IP

  44. Readout Chip Sensor +  +  SILICON MICRO - STRIP DETECTORS I miniaturisation principle pn diode as almost all semiconductor detectors typical x-y (front-back) arrangements 200 µm strips layer thickness 300 µm charged particle arrays of soldering dots

  45. silicon µ-strip module SILICON MICRO - STRIP DETECTORS II CMS - LHC scheme • inner tracker ANKE - COSY • vertex detection • recoils • polarisation (left-right asymmetry) semiconductor telescope 65/300/300/5500 µm thick double-sided Si-strip detectors

  46. EXAMPLES OF COMBINED DETECTION SYSTEMS

  47. focal plane ANKE@COSY I: SET-UP aim: measuresimultanuouslypositivelyandnegativelychargedparticles e.g., pp  pp K+ K particle identification by dE/dx 1 16 FOCAL PLANE SPECTROMETER forpositivelychargedparticles counternumber

  48. ANKE@COSY II: FOCAL PLANE DETECTOR

  49. WASA@COSY I: SET-UP aim: measurephotonsfrom neutral particledecay in coincidencewithchargedparticles e.g., dd 4He p0 gg photondetector: calorimeterchargedparticledetector: forwardhodoscope

  50. WASA@COSY II: CALORIMETER

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