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Particle Identification @ STAR

Particle Identification @ STAR. Gerd J. Kunde, Yale. TPC EMC Future RPC. Summary. Gas: P10 ( Ar-CH 4 90%-10% ) @ 1 atm Voltage : - 31 kV at the central membrane 148 V/cm over 210 cm drift path. 420 CM. TPC Gas Volume & Electrostatic Field Cage.

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Particle Identification @ STAR

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  1. Particle Identification @ STAR Gerd J. Kunde, Yale • TPC • EMC • Future RPC • Summary Pylos June 2002

  2. Gas: P10 ( Ar-CH4 90%-10% ) @ 1 atm Voltage :- 31 kV at the central membrane 148 V/cm over 210 cm drift path 420 CM TPC Gas Volume & Electrostatic Field Cage Self supporting Inner Field Cage:Al on Kapton using Nomex honeycomb; 0.5% rad length Pylos June 2002

  3. Solenoidal Magnetic Field • Magnetic Field 0.0 G ± 2.5 kG ± 5.0 kG • Radial Uniformity ±40 gauss • Phi Uniformity ± 1 gauss Pylos June 2002

  4. 60 cm 190 cm Outer and Inner Sectors of the Pad Plane • 24 sectors (12 on a side) • Large pads good dE/dx resolution in the Outer sector • Small pads for good two track resolution in the inner sector Inner sector 2.85 × 11.5 mm pads 1750 pads Outer sector 6.2 × 19.5 mm pads 3940 pads Pylos June 2002

  5. Au on Au Event at CM Energy ~ 130 GeV*A A Central Event Typically 1000 to 2000 tracks per event into the TPC Two-track separation 2.5 cm Momentum Resolution < 2% Space point resolution ~ 500 mm Rapidity coverage –1.5 < h < 1.5 Pylos June 2002

  6. Lasers for coarse value Fine adjustment from tracking matching both side of the TPC 5.45 Drift velocity (cm/ms) 5.44 1010 1020 Pressure (mbar) Drift Velocity Control Using Lasers and Tracks Pylos June 2002

  7. No wires at the boundary between the inner and outer sectors E field leak E field radial component ExB effect in R and f 0.2 Data 0.1 Residual (mm) 0. -0.1 10 20 30 Pad row # Calculation 1.6 cm Gating grid = -127 V Residual (mm) Ground plane = 0 V gap Inner sector Outer sector Inner sector Outer sector Radius (cm) Electric Field Distortions Pylos June 2002 Wieman, JT (LBNL), Long, Trentalange (UCLA)

  8. All calculated distortions Before > 200 mm 180 Track Residuals (cm) Inner sector 140 Outer sector 100 Radius (cm) After < 50 mm 60 Distortion scale ± 1.5 mm 20 Track Residuals (cm) -200 -100 0 100 200 Inner sector Outer sector Z (cm) Many Effects – B, E, Clock, Twist, CM … Pylos June 2002 Hui Long, Steve Trentelange(UCLA), JT (LBNL)

  9. Good particle separation using dE/dx 7.5% dE/dx resolution p-proton separation : > 1 GeV/c Position resolution 500 mm Function of dip angle and crossing angle 2-Track resolution 2.5 cm Momentum resolution 2% Unique features of the STAR TPC 4 meter by 4 meter scale length No field wires in the anode planes Low gain Very compact FEE electronics Analog and Digital are not synchronous Data delivered via optic fiber Uniform B and E field Distortions correctable to 50 mm Lots of physics from the year 1 data Collective flow Identified particle spectra Particle correlations Event by event physics Strangeness Future challenges Achieve turn-key operation Handle increased luminosity … Summary of Performance Achieved to Date Pylos June 2002

  10. 12 d p 8 K No calibration 9 % dE/dx (keV/cm)  With calibration 7.5% 4 m Design 6.7% e 0 Anti - 3He Offline Particle Identification by dE/dx dE/dx PID range: ~ 0.7 GeV/c for K/ ~ 1.0 GeV/c for K/p Pylos June 2002

  11. f from K+ K- pairs dn/dm background subtracted m inv dn/dm K+ K- pairs same event dist. mixed event dist. m inv Particle ID via Topology & Combinatorics Secondary vertex: Ks p + p  L p + p X  L + p  W L + K g  e++e- Ks p + + p - f  K + + K- L  p + p - r  p + + p - “kinks” K  +  Pylos June 2002

  12. W- Lbar K+ W+ f K0s L X- X+ K* STRANGENESS! (Preliminary) Pylos June 2002

  13. Two Photon Decays • 0    Branching Ratio 98.80 % •  Z  e+ e- ZConversion Probability ~ 1% • e+and e-Tracking Efficiency 60 - 90% • Overall 0 Reconstruction probability ~ 10-4  Z  e+ e- Z e+ e-   e- e+ 0      Pylos June 2002

  14.  Z  e+ e-Z . B e- e+ 4 Primary Photon Candidates Detected energy loss in the TPC TPC Z  Primary Vertex TPC 0 -200 -100 0 100 z (cm) Pizero Reconstruction r (cm) 100 Pylos June 2002 Note: Most tracks are not shown

  15. . B Topological Selection positron–electron • Opposite charged tracks • Small distance of closest approach • Small opening Angle e+ counts e- e+ e- xy distance of closest approach (cm) z distance of closest approach (cm) Pylos June 2002

  16. Primary Photon Selection Photon Momentum Vector p= pe++pe- e+ e- q Angular Difference 6000 Photon Conversion Vector q 4000 Primary Vertex counts 2000 0 0 1 2 Pylos June 2002 Angular Difference (Degrees)

  17. dE/dx 5 Conversion products dE/dx Apply photon cuts 2 electron p(GeV/c) 0 1 0.1 1 p (GeV/c) 1 -bin the deviant in photon pt -fit with a Gaussian+exp. >95% below 1Gev/c Purity 69% Minimum bias Central 0 -4 0 -4 e+ dE/dx deviant photon pt (Gev/c) Photon Purity: via positron dE/dx Pylos June 2002

  18. Extracting Yields One photon rotated by  in , 2nd order polynomial Two photon invariant mass spectrum, Gaussian + Nbg*(2nd poly) 0    After background subtraction, Gaussian Pylos June 2002

  19. x-ray like images • Photon conversion points • Conversion probability, (lZ2) • A tool not ‘just’ physics • map the detector material • improve the material layout in Geant Mc data Real data Glue joints SVT Inner Field Cage Pylos June 2002

  20. STAR Barrel Electromagnetic Calorimeter (BEMC) • Full barrel EMC • -1.0 < h < 1.0 • Full azimutal coverage • 120 modules • (Dh, Df)module ~ (1.0, 0.1) • 40 towers/module • 21 X0 • (Dh, Df)tower ~ (0.05, 0.05) • dE/E ~ 14%/√E • Shower max detector • Positioned at ~ 5 X0 • Larger spatial resolution • (Dh, Df) ~ (0.007, 0.007) • Pre-shower detector • 2 X0 • not avaliable this year Pylos June 2002

  21. BEMC patch for next run • Full West side • 60 modules • 2400 towers • 18 K SMD channels • Huge impact on physics • High-ptp0 • electrons • Jets • J/ Pylos June 2002

  22. BEMC calibration – MIP peak • Select MIP candidate • Low multiplicity event • Vertex cut to keep tower projective characteristics • Track momentum > 1.2 GeV/c • The projection of the track in the inner and outer EMC radius must be in the same tower • All adjacent towers shall not have any projected tracks • Peak + background fit • Mean ADC gain from MIP peak position • 8 MeV/ADC count 220 k minibias AuAu events |zvertex| < 40 cm pMIP > 1.2 GeV/c Pylos June 2002

  23. BEMC High tower trigger performance • Threshold set at 2 GeV • Big enhancement at high pt tracks (~30 at 6-7 GeV/c) • Enhancement at way side tracks (back-to-back jets?) Pylos June 2002

  24. p0 reconstruction with BEMC • p0 in AuAu events • 200 k minibias events • No SMD present • Only towers • Larger background • Small shift on mass value STAR preliminary Pylos June 2002

  25. e/h discrimination with BEMC • Neural network software under development • 5 parameters • Etower/ptrack • EPSD • ESMD • Width of point (Dh, Df) • Separation between point and projected track (h, f) • Hadronic suppression becomes worse without PSD • Simulations are under way Pylos June 2002

  26. Ranges of Particle Identification Pylos June 2002

  27. Resistive Plate Chambers • Narrow single gaps don’t work well in avalanche mode • Wider single gaps? • enhanced streamer-free range of operating voltage • but time resolution suffers... • primary ionziation is a stochastic process! • timing jitter from location of ionization in RPC • avalanches from single primary clusters tend to merge • fluctuations in avalanche development dominate • Many narrow gaps! • characteristic distance for primary ionization decreased • decreased timing jitter from primary ionization step • N-independent avalanches, hence an averaging • decreased timing jitter from avalanche fluctuations Pylos June 2002

  28. Comparison Pylos June 2002

  29. Alice Prototype Pylos June 2002

  30. Rice Final Prototype Pylos June 2002

  31. rpc Pylos June 2002

  32. Proposal to install 60 m2 in STAR Pylos June 2002

  33. Production of RPC at Rice Pylos June 2002

  34. FEE Breakthrough Pylos June 2002

  35. RPC Performance cell 11 (final) cell 5 Eff. Time Eff. Time Voltage (kv) Voltage (kv) Pylos June 2002

  36. RPC Summary • TOF remains a viable technique for Particle Identification in modern experiments... • MGRPC detectors are inexpensive and appear to outperform the conventional technology... • Recent Major Successes a specific fishing line is a great choice for the 220 µm spacer... • Detector module design (Rice v.11) is now final for STAR... <60ps stop-resolution is typical... • Maxim 3760 preamp & other standard components is an adequate approach to the FEE... • Collaboration of US and Chinese institutions developed... Pylos June 2002

  37. Summary • TPC • Identification via dE/dx • Topological Methods/Combinatorical Methods • Pizero • Baryons up to 5 GeV/c • EMC • Pizero • Hadron Suppression • RPC • Prototype with <60ps Stop Resolution • Proposal for 60 m2 Pylos June 2002

  38. ~400 STAR Collaborators/Institutions Brazil: Universidade de Sao Paolo China: IHEP - Beijing, IPP - Wuhan England: University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute Munich, University of Frankfurt India: Institute of Physics - Bhubaneswar, VECC Calcutta, Panjab University - Chandrigrarh, University of Rajasthan - Jaipur, Jammu University, IIT -Bombay Poland: Warsaw University, Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP - Protvinoh U.S. Labs: Argonne, Berkeley, and Brookhaven National Laboratories U.S. Universities: Arkansas, UC Berkeley, UC Davis, UCLA, Carnegie Mellon, Creighton, Indiana, Kent State, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Yale Pylos June 2002

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