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Particle Identification with TPC+TOF at STAR


									Particle Identification with

    1. Identified hadrons at high pT
    2. Electron identification at low pT

             Zhangbu Xu
     for the STAR Collaboration
           ICPAQGP, Zhangbu Xu (BNL)       1
                                                      Hadron identification:
                                                      STAR Collaboration, nucl-ex/0309012

Time Projection Chamber: 45 padrow, 2 meters (radius), s(dE/dx)8%, -1<<1
    Multi-gap Resistive Plate Chamber TOFr: 1 tray (~1/200), s(t)=85ps
                          ICPAQGP, Zhangbu Xu (BNL)                                         2
dE/dx at higher pT


Momentum: 3 < p<10 GeV/c
dE/dx of p (K,p) separation: 2s
      ICPAQGP, Zhangbu Xu (BNL)              3
                    p-(K+p) Separation

                                                         STAR Preliminary

•3 Gauss fits: dE/dx(p)>1.3*dE/dx(K)
dE/dx(p) as normal Gauss: s=1, mean=0
•p-(K+p) Separation: ~1.5-2s
• Worst Contamination:
  1-3% at 50% Eff , 10% at 70-90% Eff

                             ICPAQGP, Zhangbu Xu (BNL)                4
             Preliminary pion Spectra

                                                                p+/ p- ratio is about 1
                                                                pbar/p ~=0.5

• TPC:                 TOF:                               TPC+TOF:
   – Pion: 0-~0.6GeV/c       Pion: 0.2-~1.6GeV/c            Pion: 0.-~10 GeV/c
   – Kaon: 0.2-~0.6GeV/c     Kaon: 0.2-~1.6GeV/c            Kaon: 0.2-~3GeV/c
   – Proton: 0.2-~1 GeV/c    Proton: 0.2-~3 GeV/c           Proton: 0.2-~? GeV/c

                              ICPAQGP, Zhangbu Xu (BNL)                              5
p Nucl. Mod. Factor

                                • RCP h+- 20% higher
                                  than p+- pT=3-4 GeV/c
                                  consistent with h/pi ratio
                                • Vitev prediction at
                                • TOFr agrees with dE/dx
                                • ISR pp parametrization
                                  same as PHENIX
                                • Estimated Syst. Error:

    ICPAQGP, Zhangbu Xu (BNL)                         6
Higher  Au+Au@62                                dE/dx in d+Au@200

   STAR Preliminary


Better dE/dx resolution:                          Different particle composition
longer track, shorter drift distance              visible!!!

                               ICPAQGP, Zhangbu Xu (BNL)                      7
                                 p+- in d+Au

                                                          PRC 70(2004)064907

                                                                               STAR Preliminary

Identified pions similar to Inclusive
Au-side > d-side in all pT (upto 5 GeV/c)

Still many things to do in the near future!!!

                                  ICPAQGP, Zhangbu Xu (BNL)                                       8
          Proton PID at high pT



• Separation quite large at pT~= 10 GeV/c
• Sky is the limit!

                   ICPAQGP, Zhangbu Xu (BNL)                    9
            Dilepton Physics

• Vector Meson Properties                   R. Rapp, hep-ph/0010101
• Thermal Dileptons

                ICPAQGP, Zhangbu Xu (BNL)                         10
              A New Hadron-Blind Detector

Hadron identification:                              nucl-ex/0407006
STAR Collaboration, nucl-ex/0309012

Electron identification:
TOFr |1/ß-1| < 0.03
TPC dE/dx         electrons!!!

                                      ICPAQGP, Zhangbu Xu (BNL)       11
              Selecting Electrons

• dE/dx of fast particle
• Select electron with a
  cut: dE/dx>
• Estimate background
  from hadrons

                     ICPAQGP, Zhangbu Xu (BNL)   12
         Hadron Rejection Power
• In d+Au data, estimate
  e/h and hadron
  contamination ()
• Hadron Rejection
   – pT~=1 GeV/c:
   – pT<0.5 GeV/c:

                        ICPAQGP, Zhangbu Xu (BNL)   13
                 Dilepton Simulation
   Assume electrons can be identified with full TOF

 Total bkgd:
  ~10-4/25MeV (ω)
  ~2∙10-5/25MeV (Φ)

 Dalitz decay bkgd:
  ~5∙10-6/25MeV (ω)
  ~5∙10-7/25MeV (Φ)

Photon Conversion:
rejection by HFT inner tracker

                          ICPAQGP, Zhangbu Xu (BNL)   14
            Charm background

• One’s signal, another’s background
• Charm semi-leptonic decay (c100m)
• Rejected by HFT inner tracker (s10m)

                 ICPAQGP, Zhangbu Xu (BNL)   15
                        Rate Estimate
Assume:         dn / dy |p  1 (pp)        p  0.15          p  0.02
           dn / dy |p  300 (AuAu) s   15 MeV             s   8MeV
            TOF match+PID eff ≈ 80%            TPC+SVT+μVertex eff ≈ 60%
From PDG: Br (  e+ e- )  7  10 -5    Br (  e + e - )  3 10 -4
 Preliminary estimation for the requested data
            Au+Au                     #events for ω     #events for Φ with
                                      with 3σsignal         3σsignal
          TOF+TPC                         7M                   2M

    TOF+TPC+SVT+ HFT                     800K                 150K

                            ICPAQGP, Zhangbu Xu (BNL)                        16
•   TPC+TOF =a tracking system+a TOF + a hadron blind detector+RICH+…
    with large acceptance

•   Charged hadron identification at high pT can be done with STAR TPC (+TOF)

•   At 62.4GeV Au+Au
     – h/p ratios depend on charge, centrality and pT
     – RCP of h and pions approach each at at pT~=5 GeV/c

•   Rapidity Asymmetry of pions follows closely that of inclusive hadrons

•   More and exciting results from high pT PID capability soon.

•   TOF+TPC+HFT STAR Upgrade: Vector Meson Resonances and thermal
    dileptons are sensitive tools to study new state of matter

                            ICPAQGP, Zhangbu Xu (BNL)                           17

    ICPAQGP, Zhangbu Xu (BNL)   18

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