identified baryon and meson distributions at large transverse momenta in 200 gev au+au collisions
DESCRIPTION
Identified baryon and meson distributions at large transverse momenta in 200 GeV Au+Au collisions. L ijuan Ruan (for the STAR Collaboration) ( Lawrence Berkeley National Laboratory ). Outline: Motivation Detector and Analysis Technique Physics Results - PowerPoint PPT PresentationTRANSCRIPT
06/14/2006 Hard Probes 2006, Lijuan Ruan 1
Identified baryon and meson distributions at large transverse momenta in 200 GeV Au+Au collisions
Outline:• Motivation
• Detector and Analysis Technique
• Physics Results charged & p spectra up to 12 GeV/c from STAR
RCP, particle ratios
• Summary and Outlook
Lijuan Ruan (for the STAR Collaboration)(Lawrence Berkeley National Laboratory)
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p+p collisions and pQCD (AKK)
NLO pQCD calculations withAKK FF are consistent with pion data at high pT (> 2 GeV/c)
NLO pQCD calculations onlywith AKK FF (Nucl.Phys.B725:181-206,2005)consistent with the p+pbar data
AKK differ from KKP, in the way the light flavor FF are obtained
OPAL Collaboration : Eur. Phys. J. C 17 (2000) 207STAR Collaboration, PLB 637 (161) 2006
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Particle production in Au+Au collisions
1. p(pbar)/ ratio ~ 1 at pT~2 GeV/c.
2. Baryons (p, ) increase faster than mesons (, Ks, K) from peripheral to central collisions. consistent with the coalescence of constituent quarks at hadronization from a collective partonic system at intermediate pT. R.J. Fries, et al.,
Phys. Rev. Lett. 90 202303 (2003); R. C. Hwa, et al., Phys. Rev. C 70, 024905 (2004); V. Greco, et al., Phys. Rev. C 68, 034904(2003).
The high pT PID spectra will be presented to address the transition between coalescence and jet fragmentation.
STAR: Phys. Rev. Lett. 92 (2004) 052302
PHENIX: Phys. Rev. Lett. 91 (2003) 172301
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• In Au+Au collisions at RHIC: Fragmentation + Energy loss at pT > 6 GeV/c.
• Color charge dependence of energy loss: dE/dx(g) ≈ 9/4 dE/dx(q).
• Gluon jet contribution to protons is significantly larger than to pions at high pT in p+p collisions at RHIC. pbar vs
Color charge dependence of energy loss
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1. PID spectra, centrality dependence of pbar/p and pbar/ ratios, address the color charge dependence of energy lossTo further understand how the gluon jet/quark jet interact with the medium created in Au+Au collisions.
X.N. Wang: PRC58(2321)1998
Color charge dependence of energy loss
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STAR detector: TPC & MRPC-TOF
A new technology (TOF) ----Multi-gap Resistive Plate Chamber
adopted from CERN-Alice.1. Good timing resolution, (, K)
~1.6 GeV/c , p ~ 3 GeV/c
2. One tray (1/200 acceptance) for now, 120 trays in the future
Time Projection Chamber
1. Tracking2. Ionization energy loss (dE/dx)3. Coverage -1<<1
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Particle identification
TOF
TPC
( ,p) ~12 GeV/c
M. Shao et al., NIMA 558, (419) 2006
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Spectra
peripheral
central
STAR Preliminary
STAR: nucl-ex/0606003
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Nuclear modification factors RCP
In central Au+Au collisions:
1. At 1.5<pT<6 GeV/c, RCP(p+pbar) > RCP() , not consistent with binary scaling for proton production.
2. At pT>6 GeV/c, RCP(p+pbar) ~ RCP() . Jet fragmentation dominates over this pT region in Au+Au collisions.
I. Vitev, hep-ph/0603010.
STAR Preliminary
STAR: nucl-ex/0606003
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Anti-particle to particle ratios
1. -/+ are consistent with flat at unity in all pT, no significant centrality dependence.
2. pbar/p ratio: no significant centrality dependence, not consistent with the jet quenching prediction (X.N. Wang, PRC 58 (2321) 1998).
STAR Preliminary
STAR: nucl-ex/0606003
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Proton over pion ratios
At pT>5 GeV/c at RHIC at 200 GeV:1. p(pbar)/ are larger than the ratios from quark jet. gluon jet plays a
dominant role for protons production at RHIC. 2. p(pbar)/ (Au+Au) ~ p(pbar)/ (d+Au, p+p). No centrality dependence of
p(pbar)/ ratios. No clear color charge dependence of energy loss. 3. We expect pbar/ (Au+Au) < pbar/ (d+Au, p+p). (X.N. Wang, PRC 58 (2321) 1998)
R.J. Fries, et al., PRL 90 202303 (2003); R. C. Hwa, et al., PRC 70, 024905 (2004); DELPHI Collaboration, Eur. Phy. J. C 5, 585 (1998), Eur. Phy. J. C 17, 207 (2000).
STAR Preliminary
STAR: nucl-ex/0606003
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Summary
• The spectra of and p (pbar) from 200 GeV Au+Au collisions are presented up to pT=12 GeV/c.
• In central Au+Au collisions, at intermediate pT, RCP(p+pbar) > RCP() ; RCP(p+pbar) decreasing trend with pT, not consistent with binary scaling; the p(pbar)/ ratio~1 at pT 2~3 GeV/c.
• In central Au+Au collisions, at high pT, RCP(p+pbar) ~ RCP(), p(pbar)/ and pbar/p ratios approach the ratios in p+p and d+Au collisions.
Indicate that the partonic sources of protons and pions have similar energy loss. No clear color charge dependence of energy loss was observed.
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Discussion: energy loss in QCD matter • With the addition of collisional energy
loss in the recent calculation, the gluon jet quenching is a factor of 3 higher than quark jet quenching. (S. Wicks et al.,
nucl-th/0512076).
• Look into how gluon/quark jets interact with the medium. (Color Charge exchange: W. Liu, X.N. Wang, B. Zhang)
• Proper fragmentation functions are required.
• Systematically study the color charge dependence of energy loss measure p(pbar)/, pbar/p ratios in different energy by changing the g/q relative contribution to particle production in the future.
STAR Preliminary