Particle identification Katharina Müller, autumn 15 1 Particle identification (PID) important task for all detectors in particle and astro particle physics particle physics: B-physics, rare decays, CP violation, exotic hadronic decays quark-gluon plasma:identification of as many particles as possible astro particle physics: distinguish different nuclei, identify charged particles, photons neutrino detection distinguish π/K K/p, e/π, π0/γ .. but also neutrino/muon, ν / ν . μ e method for PID depends on energy range optimisation: efficiency and / or misidentification rate tag efficiency: ε = N / N n x x o i tag t misidentification rate ε = N / N c mis y y e j e methods: r d n mass determination u o lifetime r g k decay products c a missing energy B shower profile special detectors signal efficiency Katharina Müller, autumn 15 2 Particle ID: Example HERA-b Search for Φ→ KK physics drowned in background Φ→ KK decay only visible after particle identification Mass Φ= 1019 MeV Φ→ KK BR 48.9% Φ→ K0 K0 BR 34.2% Kaons identified L S Φ→ π+π-π0 BR 15.3% Katharina Müller, autumn 15 3 Particle ID no particle ID particle ID inivariant mass Red: signal B→D0K 3.7 10-4 Yellow: background B→D0π 4.8 10-3 Green: combinatorial background: random combinations of tracks → particle identification needed: select the right tool Katharina Müller, autumn 15 4 Particle identification ● dE/dX energy loss of charged particles → PID if momentum is known ● flight time (TOF) → velocity βc ● Cherenkov radiation (RICH) ● transition radiation (TR) ● cluster shape most detectors use several methods Katharina Müller, autumn 15 5 Example: ALICE collisions of heavy ions (Pb) at 5.5 TeV Quark-Gluon Plasma Hits in TOF red hits belong to one particle: time of flight → pion identify as many particles as possible! Katharina Müller, autumn 15 6 Example: ALICE ITS: Tracker dEdX TPC: dEdX TOF: Time of flight TRD: Transition radiation HMPID: RICH PMD: Photons PHOS: Photons Muon Arm: Muon ID Hits in TOF http://www.lhc-facts.ch/index.php?page=alice Katharina Müller, autumn 15 7 Time of fli!"t measurement (T%F) TOF: Time of flight good time resolution → scintillators length L p 2 particles (m , m ), momentum p 1 2 di#tance D L 1 1 t= − c 1 2 √1−x≃1+ x ,1/(1−x)≃1+ x , E≃ pc =1/ 1−2=E /m c2 L 1 1 L c 2 2 2 Δ t= ( − )≃ (m −m ) relativistic particles E>>mc 2 1 2 c + ( 2/ )2 + ( 2/ )2 2 p √1 m1c E1 √1 m2 c E2 (E ≃ pc and root expansion) L c non relativistic particles t= m −m p 1 2 Δt ~ Δm2/p2 : important for small velocities, large mass differences Katharina Müller, autumn 15 8 Time of fli!"t: measurement (T%&) L c ≃ 2− 2 t m1 m2 difference in TOF after 1m 2 p2 time resolution of scintillators 300 ps → kaon-pion separation up to 1 GeV with L = 3 m TOF limited for particles p < few GeV better time resolution: ● plastic scintillators: 80-300 ps ● parallel plates counters: 100-200 ps Katharina Müller, autumn 15 9 T%& measurement MeV 125 Phenix at RHIC Heavy ion physics 250 500 1000 flight distance 5 m 1000 plastic scintillators resolution 85 ps 4 σ Kaon/Pion separation p<4 GeV http://www.phenix.bnl.gov/WWW/tof/ Katharina Müller, autumn 15 10 (ELLE NA49 identification particle Trel = T/TPion Particle identificationT%& wit" Particle TOF TOF TOF and Katharina M Katharina üller, 15 autumn üller, Mass from TOF measurement TOF from Mass dE/dX 11 ALICE (T%F) TOF detector in very high multiplicity environment radius 3. 6 m → 150 m² ! scintillators too expensive → gas detectors multi gap resistive plate chambers (MGRPC) 160000 channels 2.5 x 3.5 cm² requirement: time resolution better than 100 ps MGRPC: small gap: good time resolution many gaps: high efficiency 2 x 5 gaps 250 μm 0.4 mm glass plates spacer: fishing line width 7 cm (2 Pads) length 120 cm (48 Pads) http://aliceinfo.cern.ch/Public/en/Chapter2/Chap2_TOF.html Katharina Müller, autumn 15 12 ALICE (T%F) TOF with very high multiplicity radius 3. 6 m → 150 m² ! strips: length 240 cm 96 readout pads http://aliceinfo.cern.ch/Public/en/Chapter2/Chap2_TOF.html Katharina Müller, autumn 15 13 ALICE (T%F) cleaning storage http://aliceinfo.cern.ch/Public/en/Chapter2/Chap2_TOF.html Katharina Müller, autumn 15 14 ALICE (T%F) efficiency > 99.9% Efficiency and time resolution as function resolution better than 60 ps (design 80 ps) of particle flow http://aliceinfo.cern.ch/Public/en/Chapter2/Chap2_TOF.html Katharina Müller, autumn 15 15 ALICE (T%&) Data cosmic rays: two tracks: two TOF signals Δt(exp) = L/c resolution Δt(meas)-Δt(exp) σ=125 ps two independent measurements → resolution for one track: σt =σ /√2 = 88.5 ps 2 σ k-π separation up to 5 GeV in pT http://aliceinfo.cern.ch/Public/en/Chapter2/Chap2_TOF.html http://indico.cern.ch/materialDisplay.py?contribId=191&sessionId=15&materialId=slides&confId=181055 Katharina Müller, autumn 15 16 Ener!y loss dE/dX reminder Bethe-Bloch formula -* #eparation 2 2 2 −dE Z 1 1 2 me c T max C +, re#ol$tion! =K z2 [ ln −2− − ] dX A 2 2 I2 2 Z allows to determine βγ if momentum is known difficulties: ● crossings of bands in dE/dX vs p! ● saturation ● Landau-Tail ● control measurement uncertainties ● single measurements not usable K- have a relative difference of 10% for βγ>3 → high precision (few percent) needed for significant results Katharina Müller, autumn 15 17 http://arxiv-web3.library.cornell.edu/pdf/1209.5637 ALICE dE/dX Nucl. Instr. Meth. A622 (2010) 316 TPC: σ dE/dx = 5 % (Design) Inner tracker: σ dE/dx = 10-11 % (Design) Resolution vs # TPC track points Katharina Müller, autumn 15 18 .easurement of dE/dX Problem: Bethe Bloch formula only gives the mean → single measurements have large variations (Landau distribution) → multiple measurements of dE/dX needed (sampling) better method: truncated mean x% of the measurements with highest dE/dX values are neglected (typically 20-30%), or restricted dE/dX Improvement of resolution with „truncated mean“ (KLOE) Katharina Müller, autumn 15 19 Separation Po'er important measure separation power= Separation/Resolution strong momentum dependence Opal: require 2σ Separation: e-Pion p<14.3 GeV Pion-Kaon p<20.5 GeV Katharina Müller, autumn 15 20 .easurement of Landau-distribution several measurements of dE/dX: calculate probability that measured dE/dX distribution belongs to pion, kaon, p etc i P π(x) probability that pion produces a signal x in detector i i P K(x) kaon each particle produces a set of xi signals. probability that this set of signals originates from a pion is i i Pπ = ∏i P π(xi) or for a kaon PK = ∏i P K(xi) probability that particle is a pion P = Pπ/(Pπ+PK) already few measurements are enough to reach an effective pion-kaon separation up to 100 GeV. many measurements: fit Landau distribution Katharina Müller, autumn 15 21 /)#t0 uncertainties of dE/d2 measurement • non-linearities of readout electronics • stability of discriminator threshold • purity of chamber gas. Small impurities (10-6!) change gas amplification • stability of geometry, mechanical tolerances • pressure dependence of gas amplification • charge distribution depends on scattering angle • track multiplicity changes gas/amplification • noise • crosstalk •.....etc • has to be understood at the 1% level! Katharina Müller, autumn 15 22 Alice TPC: simulated #eparation Katharina Müller, autumn 15 23 Detector Accelerator Type Size B (T) Gas Mixture Pressure Number of Sampling Effective track dE/dx resolution (∅ x L) (bar) samples length (mm) length (bar * m) isol., dense (%) ALEPH LEP TPC 3.6 m x 4.4 m 1.5 Ar/CH4 (91/9) 1 338 4 1.35 4.5 ARGUS DORIS drift cells 1.7 m x 2 m 0.8 C3H8/Methylal 1 36 18 0.65 4.1 BaBar PEP-II drift cells 1.6 m x 2.8 m 1.5 He/i-C4H10 (80/20) 1 40 12 0.48 7.5 BELLE KEK-B drift cells 1.9 m x 2.2 m 1.5 He/C2H6 (50/50) 1 47 16 0.75 5.5 BES BEPC jet cells 2.3 m x 2.1 m 0.4 Ar/CO2/CH4 (89/10/1) 1 54 5 0.27 9.0 CDF TEVATRON jet cells 2.6 m x 3.2 m 1.5 Ar/C2H6/C2H6O (49.6/49.6/0.8) 1 32 12 0.38 7.0 CLEO II CESR drift cells 1.9 m x 1.9 m 1.5 Ar/C2H6 (50/50) 1 51 14 0.71 6.2 CLEO III CESR drift cells 1.6 m x 1.9 m 1.5 He/C3H8 (60/40) 1 47 14 0.66 5.0 CRISIS TEVATRON jet cells 1 m x 1 m x 3 m - Ar/CO2 (80/20) 1 192 15 2.88 3.2 DELPHI LEP TPC 2.4 m x 2.7 m 1.2 Ar/CH4 (80/20) 1 192 4 0.77 5.7 D0 FDC TEVATRON jet cells 1.2 m x 0.3 m - Ar/CH4/CO2 (93/4/3) 1 32 8 0.26 12.7 H1 HERA jet cells 1.7 m x 2.2 m 1.13 Ar/C2H6 (50/50) 1 56 10 0.56 10.0 JADE PETRA jet cells 1.6 m x 2.4 m 0.48 Ar/CH4/i-C4H10 (88.7/8.5/2.8) 4 48 10 1.92 6.5 KEDR VEPP-4M jet cells 1.1 m x 1.1 m 2.0 DME (100) 1 42 10 0.42 10.0 KLOE DAΦNE drift cells 4 m x 3.3 m 0.6 He/i-C4H10 (90/10) 1 58 28 1.62 3.5 MARK II SLC drift cells 3 m x 2.3 m 0.475 Ar/CO2/CH4 (89/10/1) 1 72 8.33 0.60 7.0 NA49 SPS TPC 3.8 m x 3.8 m x 1.3 m - Ar/CH4/CO2 (90/5/5) 1 90 40 3.60 4.7 OBELIX LEAR jet cells 1.6 m x 1.4 m 0.5 Ar/C2H6 (50/50) 1 40 15 0.60 12.0 OPAL LEP jet cells 3.6 m x 4 m 0.435 Ar/CH4/i-C4H10 (88.2/9.8/2) 4 159 10 6.36 2.8 SLD SLC jet cells 2 m x 2 m 0.6 CO2/Ar/i-C4H10 (75/21/4) 1 80 6 0.48 7.0 STAR RHIC TPC 4 m x 4.2 m 0.5 Ar/CH4 (90/10) 1 45 17.2 0.77 8.0 TOPAZ TRISTAN TPC 2.4 m x 2.2 m 1.0 Ar/CH4 (90/10) 3.5 175 4 2.45 4.4 TPC/2γ PEP TPC 2 m x 2 m 1.375 Ar/CH4 (80/20) 8.5 183 4 6.22 3.0 ZEUS HERA jet cells 1.7 m x 2.4 m 1.43 Ar/CO2/C2H6 (90/8/2) 1 72 8 0.58 8.5 Alice: 5% resolution best performance: large detectors & high pressure Katharina Müller, autumn 15 24 Di3erent approac": Cluster Countin! traditionally dE/dx measurements integrate all charge deposited on the wire as a proxy for number of primary ionisation fluctuations in gas gain and number of primary electrons degrades measurements counting primary ionization