identified baryon and meson distributions at large transverse momenta in 200 gev au+au collisions

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06/14/2006 Hard Probes 2006, Liju an 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 R CP , particle ratios Summary and Outlook Lijuan Ruan (for the STAR Collaboration) (Lawrence Berkeley National Laboratory)

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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 Presentation

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Page 1: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

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)

Page 2: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 2

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

Page 3: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 3

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

Page 4: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 4

• 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

Page 5: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 5

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

Page 6: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 6

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

Page 7: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 7

Particle identification

TOF

TPC

( ,p) ~12 GeV/c

M. Shao et al., NIMA 558, (419) 2006

Page 8: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 8

Spectra

peripheral

central

STAR Preliminary

STAR: nucl-ex/0606003

Page 9: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 9

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

Page 10: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 10

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

Page 11: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 11

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

Page 12: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 12

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.

Page 13: Identified baryon and meson distributions at large transverse momenta  in 200 GeV Au+Au collisions

06/14/2006 Hard Probes 2006, Lijuan Ruan 13

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