Particle Detectors. Summer Student Lectures 2007 Werner Riegler, CERN, History of Instrumentation History of Particle Physics

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1 Particle Detectors Summer Student Lectures 2007 Werner Riegler, CERN, History of Instrumentation History of Particle Physics The Real World of Particles Interaction of Particles with Matter, Tracking detectors Resistive Plate Chambers, Calorimeters, Particle Identification Detector Systems W. Riegler/CERN 1

2 Gas Detectors with internal Electron Multiplication Parallel Plate Avalanche Chamber (PPAC) Resistive Plate Chamber W. Riegler/CERN 2

3 Resistive Plate Chambers (RPCs) Keuffel Spark Counter: High voltage between two metal plates. Charged particle leaves a trail of electrons and ions in the gap and causes a discharge (Spark). Excellent Time Resolution(<100ps). Discharged electrodes must be recharged Dead time of several ms. Parallel Plate Avalanche Chambers (PPAC): At more moderate electric fields the primary charges produce avalanches without forming a conducting channel between the electrodes. No Spark induced signal on the electrodes. Higher rate capability. However, the smalles imperfections on the metal surface cause sparcs and breakdown. Very small (few cm 2 ) and unstable devices. In a wire chamber, the high electric field ( kV/cm) that produces the avalanche exists only close to the wire. The fields on the cathode planes area rather small 1-5kV/cm. W. Riegler/CERN 3

4 Resistive Plate Chambers (RPCs) Place resistive plates in front of the metal electrodes. No spark can develop because the resistivity together with the capacitance (tau ~ e*ρ) will only allow a very localized discharge. The rest of the entire surface stays completely unaffected. Large area detectors are possible! Resistive plates from Bakelite (ρ = Ωcm) or window glass (ρ = Ωcm). Gas gap: mm. Elektric Fields kV/cm. Time resolutions: 50ps (100kV/cm), 1ns(50kV/cm) Application: Trigger Detectors, Time of Flight (TOF) Resistivity limits the rate capability: Time to remove avalanche charge from the surface of the resistive plate is (tau ~ e*ρ) = ms to s. Rate limit of khz/cm 2 for Ωcm. W. Riegler/CERN 4

5 ALICE TOF RPCs 130 mm active area 70 mm Several gaps to increase efficiency. Stack of glass plates. Small gap for good time resolution: 0.25mm. Flat cable connector Differential signal sent from strip to interface card M5 nylon screw to hold fishing-line spacer honeycomb panel (10 mm thick) PCB with cathode pickup pads external glass plates 0.55 mm thick internal glass plates (0.4 mm thick) PCB with anode pickup pads PCB with cathode pickup pads Honeycomb panel (10 mm thick) Mylar film (250 micron thick) 5 gas gaps of 250 micron Fishing lines as high precision spacers! Large TOF systems with 50ps time resolution made from window glass and fishing lines! Before RPCs Scintillators with very special photomultipliers very expensive. Very large systems are unafordable. connection to bring cathode signal Silicon sealing compound to central read-out PCB W. Riegler/CERN 5

6 Elektro-Magnetic Interaction of Charged Particles with Matter Classical QM 1) Energy Loss by Excitation and Ionization 2) Energy Loss by Bremsstrahlung 3) Cherekov Radiation and 4) Transition Radiation are only minor contributions to the energy loss, they are however important effects for particle identification. W. Riegler/CERN 6

7 Bremsstrahlung, semi-classical: A charged particle of mass M and charge q=z 1 e is deflected by a nucleus of Charge Ze. Because of the acceleration the particle radiated EM waves energy loss. Coulomb-Scattering (Rutherford Scattering) describes the deflection of the particle. Maxwell s Equations describe the radiated energy for a given momentum transfer. de/dx W. Riegler/CERN 7

8 Proportional to Z 2 /A of the Material. Proportional to Z 14 of the incoming particle. Proportional zu ρ of the particle. Proportional 1/M 2 of the incoming particle. Proportional to the Energy of the Incoming particle E(x)=Exp(-x/X 0 ) Radiation Length X 0 M 2 A/ (ρ Z 14 Z 2 ) X 0 : Distance where the Energy E 0 of the incoming particle decreases E 0 Exp(-1)=0.37E 0. W. Riegler/CERN 8

9 Critical Energy For the muon, the second lightest particle after the electron, the critical energy is at 400GeV. The EM Bremsstrahlung is therefore only relevant for electrons at energies of past and present detectors. Elektron Momentum MeV/c Critical Energy: If de/dx (Ionization) = de/dx (Bremsstrahlung) Myon in Copper: p 400GeV Electron in Copper: p 20MeV W. Riegler/CERN 9

10 For Eγ>>m e c 2 =0.5MeV : λ = 9/7X 0 Average distance a high energy photon has to travel before it converts into an e + e - pair is equal to 9/7 of the distance that a high energy electron has to travel before reducing it s energy from E 0 to E 0 *Exp(-1) by photon radiation. W. Riegler/CERN 10

11 Electro-Magnetic Shower of High Energy Electrons and Photons W. Riegler/CERN 11

12 W. Riegler/CERN 12

13 Electro-Magnetic Shower of High Energy Electrons and Photons W. Riegler/CERN 13

14 Calorimetry: Energy Measurement by total Absorption of Particles W. Riegler/CERN 14

15 Calorimetry: Energy Measurement by total Absorption of Particles Liquid Nobel Gases (Nobel Liquids) Scintillating Crystals, Plastic Scintillators (sampling) W. Riegler/CERN 15

16 EM Calorimetry Crystals Noble Liquids W. Riegler/CERN 16

17 EM Calorimetry Direct CP violation experiments NA48, KTeV Excellent EM Calorimetry for π 0 measurement. X 0 = 4.7cm ρ = 2.41 g/cm 3 ρ M = 5.5cm X 0 = 1.85cm ρ = 4.51 g/cm 3 ρ M = 3.5cm W. Riegler/CERN 17

18 Hadronic Showers W. Riegler/CERN 18

19 Hadron Calorimeters W. Riegler/CERN 19

20 Sampling Calorimeters W. Riegler/CERN 20

21 W. Riegler/CERN 21

22 Particle Identification W. Riegler/CERN 22

23 de/dx Measured energy loss average energy loss In certain momentum ranges, particles can be identified by measuring the energy loss. W. Riegler/CERN 23

24 Time of Flight (TOF) NA49 combined particle ID: TOF + de/dx (TPC) W. Riegler/CERN 24

25 Cherenkov Radiation W. Riegler/CERN 25

26 Ring Imaging Cherenkov Detector W. Riegler/CERN 26

27 LHCb RICH W. Riegler/CERN 27

28 Transition Radiation W. Riegler/CERN 28

29 Detector Systems, Selected Experiments ALICE: Donut: CNGS: Amanda: AMS: Heavy Ion Experiment at CERN Neutrino Experiment at Fermilab Long Baseline Neutrino Experiment CERN/Gran Sasso Neutrino Experiment at the Southpole Particle Physics Experiment in Space Thanks to Heinrich Schindler W. Riegler/CERN 29

30 ALICE A heavy Ion Experiment at the LHC. W. Riegler/CERN 30

31 ALICE W. Riegler/CERN 31

32 ALICE Alice uses ~ all known techniques! TPC + ITS (de/dx) π/k K/p e /π TOF e /π π/k K/p HMPID (RICH) p (GeV/c) π/k TPC (rel. rise) π /K/p K/p TRD e /π PHOS γ /π 0 π/k K/p p (GeV/c) W. Riegler/CERN 32

33 ALICE TPC NA49 LHC: dn ch /dy = ALICE 'worst case' scenario: dn ch /dy = 8000 STAR 33

34 W. Riegler/CERN 34

35 AMANDA Antarctic Muon And Neutrino Detector Array W. Riegler/CERN 35

36 AMANDA South Pole W. Riegler/CERN 36

37 AMANDA W. Riegler/CERN 37

38 AMANDA Look for upwards going Muons from Neutrino Interactions. Cherekov Light propagating through the ice. Find neutrino point sources in the universe! W. Riegler/CERN 38

39 Event Display AMANDA Up to now: No significant point sources but just neutrinos from cosmic ray interactions in the atmosphere were found. Ice Cube for more statistics! W. Riegler/CERN 39

40 DONUT Detector for Observation of Tau Neutrino. W. Riegler/CERN 40

41 DONUT W. Riegler/CERN 41

42 DONUT W. Riegler/CERN 42

43 DONUT Tau lepton has very short lifetime and is therefore identified by the characteristic kink on the decay point. W. Riegler/CERN 43

44 DONUT One of the 4 tau candidates. Emulsion resolution 0.5um! W. Riegler/CERN 44

45 CERN Neutrino Gran Sasso (CNGS) W. Riegler/CERN 45

46 If neutrinos have mass: CNGS ν e Muon neutrinos produced at CERN. See if tau neutrinos arrive in Italy. ν μ ν τ W. Riegler/CERN 46

47 CNGS (CERN Neutrino Gran Sasso) CNGS Project A long base-line neutrino beam facility (732km) send ν μ beam produced at CERN detect ν τ appearance in OPERA experiment at Gran Sasso direct proof of ν μ - ν τ oscillation (appearance experiment) W. Riegler/CERN 47

48 CNGS W. Riegler/CERN 48

49 Neutrinos at CNGS: Some Numbers For 1 day of CNGS operation, we expect: protons on target 2 x pions / kaons at entrance to decay tunnel 3 x ν μ in direction of Gran Sasso ν μ in 100 m 2 at Gran Sasso 3 x ν μ events per day in OPERA ν τ events (from oscillation) 25 per day 2 per year W. Riegler/CERN 49

50 CNGS Layout 800m 100m 1000m 26m 67m vacuum p + C (interactions) π +, K + (decay in flight) μ + + ν μ W. Riegler/CERN 50

51 CNGS W. Riegler/CERN 51

52 CNGS W. Riegler/CERN 52

53 Radial Distribution of the ν μ -Beam at GS Flat top: 500m FWHM: 2800m 5 years CNGS operation, 1800 tons target: neutrino interactions ~150 ντ interactions ~15 ντ identified < 1 event of background typical size of a detector at Gran Sasso W. Riegler/CERN E. Gschwendtner, CERN 53

Emulsions: micrometric precision brick Brick 1 mm ν τ 8.3kg 10.

54 Opera Experiment at Gran Sasso Basic unit: brick 56 Pb sheets + 56 photographic films (emulsion sheets) Lead plates: massive target Emulsions: micrometric precision brick Brick 1 mm ν τ 8.3kg 10.2 x 12.7 x 7.5 cm 3 Pb Couche de gélatine photographique 40 μm W. Riegler/CERN 54

Particle Detectors. Summer Student Lectures 2010 Werner Riegler, CERN, History of Instrumentation History of Particle Physics

Particle Detectors. Summer Student Lectures 2010 Werner Riegler, CERN, History of Instrumentation History of Particle Physics Particle Detectors Summer Student Lectures 2010 Werner Riegler, CERN, werner.riegler@cern.ch History of Instrumentation History of Particle Physics The Real World of Particles Interaction of Particles