Particle Detectors A brief introduction with emphasis on high energy physics applications TRIUMF Summer Institute 2006 July 10-21 2006 Lecture I measurement of ionization and position Lecture II scintillation and photo detection calorimetry Lecture III particle identification detector systems Michel Lefebvre Physics and Astronomy University of Victoria
Lecture III Particle Identification de/dx measurement Time of flight Cherenkov detectors Transition radiation detectors Detector systems TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/2
Particle ID with de/dx Particle ID using a TPC measure de/dx many times along tracks measure momentum from curvature in B field multihadron events in e + e - PEP4/9 Particle Data Group collisions. muons from pion decays are separated at low momentum. pions and kaons are separated almost in the whole momentum range electrons reach Fermi plateau at 1.4 MIP protons and deuterons come from hadron nucleus collisions in materials such as the beam pipe TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/3
Particle ID with de/dx Particle ID using a silicon detector DELPHI microvertex detector (3 300 µm Si) simulation de/dx arbitrary units log p (GeV/c) data log p (GeV/c) Joram TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/4
Particle ID with time of flight Combine TOF with momentum measurement t = L p = γmβ β c p ( )2 2 m= = p β 1= p ct 1 γβ L start stop 2 2 2 2 σ p 4 σl σt σm m = +γ + p L t Consider the TOF difference for two particles at a given momentum 2 2 mc mc p mc t t t L 1 1 = = + Lc m m c p + p 2 p ( 2 2) 1 2 1 2 2 1 2 TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/5
Particle ID with time of flight Example: CERN NA49 heavy ion experiment t / t π combine m 2 from TOF and de/dx of TPC! TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/6
Particle ID with Cherenkov radiation Cherenkov radiation charged particle travels faster than light in medium β > 1 n c t n θ β c t number of photons emitted x ring of light θc 1 energy loss small (~1%) compared to ionization cos θ C = nβ θ C = θ C (E γ ) since in general n = n(e γ ) d N de dx αz 2 2 2 = sin θc γ c ( E ) 370sin θ ev cm 2 1 1 C γ medium n θ max (β=1) N ph (ev -1 cm -1 ) air 1.000283 1.36 0.208 isobutane 1.00127 2.89 0.941 water 1.33 41.2 160.8 quartz 1.46 46.7 196.4 Joram TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/7
Particle ID with Cherenkov radiation Threshold detector N β> 2 2 1 1 1 1 1 mc = + 2 2 2 2 n β n p 1 n radiator medium mirror PM particle Study of an aerogel threshold detector for the BELLE experiment at KEK β kaon ; light yield (a.u.) 1.1 1.0 0.9 0.8 β kaon n=1.03 0.7 0.6 0.5 n=1.02 0.4 0.3 0.2 0.1 n=1.01 0.0 0 1 2 3 4 5 6 p kaon [GeV/c] Joram TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/8
Particle ID with Cherenkov radiation Ring imaging Cherenkov detector (RICH) mesure θ C with a photosensitive plane need large area photo detector cos C wire chambers with photosensitive gas PMT arrays θ = 1 n β charged current θ C e - scattering SNO has 10000 PMT s TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/9
Transition radiation detector Transition radiation energy radiated when a z charged particle crosses the boundary between vacuum and a dielectric layer W = ωp α ω γ γ 1 3 p 20 ev only high energy e ± will emit transition radiation for plastic radiators, ω p is the plasma frequency number of photons emitted per boundary is small ( 1 ) 2 p z Nγ ω> 10 γ ω = 0.59% need many boundaries! For example you can build a stack with many foils with gas gaps photons are emitted close to the track typical energy is in the kev range ω 1 θ γ γ ω 1 4 p TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/10
Transition radiation detector Transition radiation radiators low Z material preferred to keep re-absorption small ( Z 5 ) stacks of CH 2 foils hydrocarbon foam and fibre materials Transition radiation X-ray detectors should be sensitive for 3 E γ 30 kev MWPC, drift chamber, straw tubes, etc. gas with high Z to increase photoelectric effect ( Z 5 ) for example Xe (Z = 54) TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/11
Transition radiation detector Pulse height (1 cm Xe) de/dx 200 e - TR (10 kev) 500 e - Joram t ATLAS Transition radiation Tracker using about 400 000 straw tubes detectors with Xe based gas Discrimination by threshold TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/12
Detector systems Measure for each event numbers of particles produced particle identification particle energy and/or momentum event topology Geometrical configurations traget fixed target tracking muon filter N collider detector system S beam magnet calorimeter (dipole) Limited solid angle dω coverage rel. easy access (cables, maintenance) barrel endcap endcap full dω coverage very restricted access TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/13
Detector systems Magnetic field configurations solenoid B toroid B Large homogeneous field inside the coil Week opposite field in the return yoke Cost limits the size Relatively high material budget Examples: DELPHI (SC, 1.2T) L3 (NC, 0.5T) CMS (SC, 4T) Relatively large fields over large volume Relatively low material budget Non-uniform field Complex structure Example: ATLAS (Barrel air toroid, SC, 0.6T) TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/14
Detector systems Typical detector components Need good e/γ, e/jet, γ/jet separation TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/15
Detector systems Typical arrangement ATLAS and CMS require high precision tracking also for high energetic muons: large muon systems with high spatial resolution behind calorimeters. Low density high density high precision low precision high granularity low granularity track density 1/r 2 e - γ µ + vertex location (Si detectors) p main tracking (gas or Si detectors) particle identification e.m. calorimetry magnet coil Joram hadron calorimetry / return yoke muon identification / tracking TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/16
Event Triggering Much more difficult at LHC than at e + e - machines interaction rate ~ 10 9 events/s acquisition capacity ~ 100 events/s @ ~1MByte/event trigger rejection factor or ~ 10 7 trigger decision time ~ 1 µs >> 25 ns need to store large amount of data in pipelines while the trigger performs calculations detector pipeline keep 10 9 events/s 10 9 events/s LVL 3 reject 10 2 events/s TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/17
ATLAS Detector A Toroidal Lhc ApparatuS length: 40 m radius: 10 m weight: 7 kt ~10 8 elec. ch human TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/18
CMS Detector Compact Muon Solenoid human TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/19
ATLAS and CMS F. Gianotti, ATL- CONF- 2000-001 TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/20
ATLAS web cam TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/21
ATLAS Detector Components ATLAS barrel cryostat, containing the solenoid and the electromagnetic barrel calorimeter, being lowered in the pit TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/22
ATLAS Detector Components TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/23
Lecture III: Questions Question III.1 Obtain the result for the error on the mass given on slide III/5. Question III.2 Consider the separation of two particles using a time of flight detector. With a flight path of 1.0 m and a timing resolution of 200 ps, up to which momentum can you separate a π + from a K +? TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/24
Acknowledements Christian Joram (CERN) I have taken a lot of material from his very fine CERN summer Student Lectures 2003 Steinar Stapnes For his help with lecture material TSI06 organizing committee and TRIUMF hosts! TRIUMF Summer Institute 2006, Particle Detectors Michel Lefebvre, Victoria III/25