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DNP2004, Zhangbu Xu (BNL) 1
Charged pion pT spectra in Au+Au
collisions at 62.4 GeV
Zhangbu Xu
BNL
for the STAR Collaboration
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DNP2004, Zhangbu Xu (BNL) 2
Time Projection Chamber: 45 padrow, 2 meters (radius), dE/dx)8%, -1<Multi-gap Resistive Plate Chamber TOFr: 1 tray (~1/200), (t)=85ps
Hadron identification: STAR Collaboration, nucl-ex/0309012
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DNP2004, Zhangbu Xu (BNL) 3
A New Hadron-Blind Detector
Electron identification: TOFr |1/ß-1| < 0.03 TPC dE/dx electrons!!!
nucl-ex/0407006 Hadron identification: STAR Collaboration, nucl-ex/0309012
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DNP2004, Zhangbu Xu (BNL) 4
dE/dx at higher pT
Momentum: GeV/cdE/dx of K,p) separation: 2
10~
3 p
Log10(p)
Log
10(d
E/d
x)
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DNP2004, Zhangbu Xu (BNL) 5
-(K+p) Separation
• Worst Contamination: 1-3% at 50% Eff , 10% at 70-90% Eff
STAR Preliminary
•3 Gauss fits: dE/dx()>1.3*dE/dx(K)dE/dxas normal Gauss: =1, mean=0-(K+p) Separation: ~1.5-2
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DNP2004, Zhangbu Xu (BNL) 6
Preliminary pion Spectra
• TPC: – Pion: 0-~0.6GeV/c
– Kaon: 0.2-~0.6GeV/c
– Proton: 0.2-~1 GeV/c
TOF: Pion: 0.2-~1.6GeV/c Kaon: 0.2-~1.6GeV/c Proton: 0.2-~3 GeV/c
TPC+TOF: Pion: 0.-~10 GeV/c Kaon: 0.2-~3GeV/c Proton: 0.2-~5 GeV/c
+/ - ratio is about 1pbar/p ~=0.5
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DNP2004, Zhangbu Xu (BNL) 7
h/ ratios
• h/ peripheral<central but approach each other at pT>5GeV/c for both negative and positive
• (K+p)/ Positive=2*Negative50% higher in central than in peripheral
• (h++h-)/(++ -) about 20% higher in central than in peripheral
+/ - ratio is about 1.
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DNP2004, Zhangbu Xu (BNL) 8
Nucl. Mod. Factor
• RCP h+- 20% higher than +- pT=3-4 GeV/cconsistent with h/pi ratio
• Vitev prediction at dN/dy=650
• TOFr agrees with dE/dx +-
• ISR pp parametrization same as PHENIX
• Estimated Syst. Error: 5-10%
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DNP2004, Zhangbu Xu (BNL) 9
Higher
Better dE/dx resolution: longer track, shorter drift distance
STAR Preliminary
0.5<||<0.9
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DNP2004, Zhangbu Xu (BNL) 10
Conclusions• TPC+TOF =a tracking system+a TOF + a hadron
blind detector+RICH+…• Charged pion identification at high pT can be done
with STAR TPC (+TOF)• At 62.4GeV Au+Au, h/ratios depend on charge,
centrality and pT– Central collisions: decrease with pT to approach peripheral value
(at pT=6-7GeV/c) – Central Collisions: (h+/+)-(h-/-)~=1 (pT=3GeV/c)
• RCP of h and different by ~20%• Study dependence around mid-rapidity• More to come!!!