1. g.j.kunde@yale.eduPylos June 20021 Particle Identification @ STAR Gerd J. Kunde, Yale  TPC  EMC  Future RPC  Summary

2. g.j.kunde@yale.eduPylos June 20022 STAR Detector (year-by-year) 1 st year detectors (2000) year-by-year implementation until 2003 2 nd year detectors (2001) Silicon Vertex Tracker Central Trigger Barrel Forward Time Projection Chambers Time Projection Chamber Barrel EM Calorimeter Vertex Position Detectors Endcap Calorimeter Magnet Coils TPC Endcap & MWPC RICH Silicon Strip Detector Photon Multiplicity Detector ZeroDegree Calorimeter + TOF patch

3. g.j.kunde@yale.eduPylos June 20023 420 CM TPC Gas Volume & Electrostatic Field Cage Gas: P10 ( Ar-CH 4 90%-10% ) @ 1 atm Voltage : - 31 kV at the central membrane 148 V/cm over 210 cm drift path Self supporting Inner Field Cage: Al on Kapton using Nomex honeycomb; 0.5% rad length

4. g.j.kunde@yale.eduPylos June 20024 Solenoidal Magnetic Field Magnetic Field 0.0 G  2.5 kG  5.0 kG Radial Uniformity  40 gauss Phi Uniformity  1 gauss

5. g.j.kunde@yale.eduPylos June 20025 Outer and Inner Sectors of the Pad Plane 60 cm 190 cm Outer sector 6.2 × 19.5 mm pads 3940 pads Inner sector 2.85 × 11.5 mm pads 1750 pads 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

6. g.j.kunde@yale.eduPylos June 20026 Au on Au Event at CM Energy ~ 130 GeV*A Two-track separation 2.5 cm Momentum Resolution < 2% Space point resolution ~ 500  m Rapidity coverage –1.5 <  < 1.5 A Central Event Typically 1000 to 2000 tracks per event into the TPC

7. g.j.kunde@yale.eduPylos June 20027 Drift Velocity Control Using Lasers and Tracks Pressure (mbar) 5.44 5.45 Drift velocity (cm/  s) 10101020 Lasers for coarse value Fine adjustment from tracking matching both side of the TPC

8. g.j.kunde@yale.eduPylos June 20028 Electric Field Distortions No wires at the boundary between the inner and outer sectors –E field leak E field radial component ExB effect in R and  Outer sector Inner sector Gating grid = -127 V Ground plane = 0 V 1.6 cm Pad row #102030 Data Residual (mm) 0.2 0.1 -0.1 0. Residual (mm) Calculation gap Inner sectorOuter sector Radius (cm) Wieman, JT (LBNL), Long, Trentalange (UCLA)

9. g.j.kunde@yale.eduPylos June 20029 Many Effects – B, E, Clock, Twist, CM … Hui Long, Steve Trentelange(UCLA), JT (LBNL) All calculated distortions 20 60 100 140 -2002000-100100 180 Z (cm) Radius (cm) Distortion scale  1.5 mm Outer sector Inner sector Track Residuals (cm) Before > 200  m Inner sector Outer sector Track Residuals (cm) After < 50  m

10. g.j.kunde@yale.eduPylos June 200210 Summary of Performance Achieved to Date Good particle separation using dE/dx – 7.5% dE/dx resolution –  -proton separation : > 1 GeV/c Position resolution –500  m –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  m 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 …

11. g.j.kunde@yale.eduPylos June 200211 Offline Particle Identification by dE/dx 6.7%Design 7.5%With calibration 9 %No calibration 12  K p d e  dE/dx (keV/cm) 0 8 4 Anti - 3 He dE/dx PID range: ~ 0.7 GeV/c for K /  ~ 1.0 GeV/c for K/p

12. g.j.kunde@yale.eduPylos June 200212 Particle ID via Topology & Combinatorics Secondary vertex: K s   +  p +    +   + K  e + +e - K s   + +  -   K + + K -   p +  -    + +  -  from K + K - pairs K + K - pairs m inv same event dist. mixed event dist. background subtracted dn/dm “ kinks ” K     +

13. g.j.kunde@yale.eduPylos June 200213 STRANGENESS! (Preliminary) K0sK0s  K+K+     ba r   

14. g.j.kunde@yale.eduPylos June 200214 Two Photon Decays  0    Branching Ratio 98.80 %  Z  e + e - Z  Z  e + e - Z Conversion Probability ~ 1% e + and e -e + and e - Tracking Efficiency 60 - 90% Overall  0 Reconstruction probability ~ 10 -4  0         e+e+ e-e- e+e+ e-e-   Z  e + e - Z

15. g.j.kunde@yale.eduPylos June 200215 Pizero Reconstruction r (cm) 100 z (cm)0-100-200100 0 TPC 4 Primary Photon Candidates Primary Vertex e-e- e+e+ Z   Z  e + e -  Z  e + e - Z Detected energy loss in the TPC B. Note: Most tracks are not shown

16. g.j.kunde@yale.eduPylos June 200216 xy distance of closest approach (cm) z distance of closest approach (cm) Opposite charged tracks Small distance of closest approach Small opening Angle e-e- e+e+ e+e+ e-e- count s Topological Selection B. positron – electron

17. g.j.kunde@yale.eduPylos June 200217 Primary Photon Selection p  = p e + + p e -  Primary Vertex Photon Momentum Vector  e+e+ e-e- Photon Conversion Vector Angular Difference counts Angular Difference (Degrees) 4000 2000 6000 210 0

18. g.j.kunde@yale.eduPylos June 200218 Photon Purity: via positron dE/dx photon p t (Gev/c) Purity 69% -40 1 0 e + dE/dx deviant p (GeV/c) 10.1 dE/dx 5 2 electron p(GeV/c) 10 Conversion products Minimum bias Central >95% below 1Gev/c -bin the deviant in photon p t -fit with a Gaussian+e xp. Apply photon cuts

19. g.j.kunde@yale.eduPylos June 200219 Extracting Yields One photon rotated by  in , 2 nd order polynomial Two photon invariant mass spectrum, Gaussian + N bg *(2 nd poly) After background subtraction, Gaussian 0   0   

20. g.j.kunde@yale.eduPylos June 200220 x-ray like images Photon conversion points –Conversion probability, (  lZ 2 ) A tool not ‘just’ physics –map the detector material –improve the material layout in Geant Inner Field Cage SVT Glue joints Mc data Real data

21. g.j.kunde@yale.eduPylos June 200221 STAR Barrel Electromagnetic Calorimeter (BEMC) Full barrel EMC –-1.0 <  < 1.0 –Full azimutal coverage –120 modules (  ) module ~ (1.0, 0.1) 40 towers/module –21 X 0 –(  ) tower ~ (0.05, 0.05) –  E/E ~ 14%/√E Shower max detector –Positioned at ~ 5 X 0 –Larger spatial resolution –(  ) ~ (0.007, 0.007) Pre-shower detector –2 X 0 –not avaliable this year

22. g.j.kunde@yale.eduPylos June 200222 BEMC patch for next run Full West side –60 modules 2400 towers 18 K SMD channels Huge impact on physics –High-p t  0 –electrons –Jets –J/ 

23. g.j.kunde@yale.eduPylos June 200223 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 |z vertex | < 40 cm p MIP > 1.2 GeV/c

24. g.j.kunde@yale.eduPylos June 200224 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?)

25. g.j.kunde@yale.eduPylos June 200225  0 reconstruction with BEMC  0 in AuAu events –200 k minibias events –No SMD present Only towers Larger background Small shift on mass value STAR preliminary

26. g.j.kunde@yale.eduPylos June 200226 e/h discrimination with BEMC Neural network software under development 5 parameters –E tower /p track –E PSD –E SMD –Width of point (  ) –Separation between point and projected track (  ) Hadronic suppression becomes worse without PSD –Simulations are under way

27. g.j.kunde@yale.eduPylos June 200227 rpc

28. g.j.kunde@yale.eduPylos June 200228 rpc

29. g.j.kunde@yale.eduPylos June 200229 Ranges of Particle Identification

30. g.j.kunde@yale.eduPylos June 200230 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

31. g.j.kunde@yale.eduPylos June 200231 Comparison

32. g.j.kunde@yale.eduPylos June 200232 Alice Prototype

33. g.j.kunde@yale.eduPylos June 200233 Rice Final Prototype

34. g.j.kunde@yale.eduPylos June 200234 rpc

35. g.j.kunde@yale.eduPylos June 200235 Proposal to install 60 m 2 in STAR

36. g.j.kunde@yale.eduPylos June 200236 Production of RPC at Rice

37. g.j.kunde@yale.eduPylos June 200237 FEE Breakthrough

38. g.j.kunde@yale.eduPylos June 200238 RPC Performance Voltage (kv) TimeEff. Time cell 5 cell 11 (final)

39. g.j.kunde@yale.eduPylos June 200239 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...

40. g.j.kunde@yale.eduPylos June 200240 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 m 2

41. g.j.kunde@yale.eduPylos June 200241 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. 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 U.S. Labs: Argonne, Berkeley, and Brookhaven National Laboratories ~400