Identified particle transverse momentum distributions

in 200 GeV Au+Au collisions at RHIC

刘海东中国科技大学

Haidong Liu (USTC) 2

Main contribution Identified charged hadron spectra

PRL 97 (2006) 152301 (cited by 61 articles )

nucl-ex 0606003 (cited by 26 articles)

Light nuclei spectra and v2 J. Phys. G: Nucl. Part Phys. 34(2007) S1087-s1091 (cited by

3 articles ) International Journal of Modern Physics E ， Vol: 16 Issue:

10 (2007) Page: 3280 - 3285 Anti-baryon phase space density study

nucl-ex/0610035 Submitted to PLB

Haidong Liu (USTC) 3

Outline

Motivation Detectors and measurement Results (RHIC run 4 AuAu 200

GeV)

Haidong Liu (USTC) 4

Heavy-ion collisions at RHIC

Time

initial state

pre-equilibrium(high Q2 interactions)

QGP andhydrodynamic expansion

hadronization

freeze-out

Physics: 1) Parton distributions in nuclei 2) Initial conditions of the collision 3) A new state of matter – Quark-Gluon Plasma and its properties 4) Hadronization and freeze-out

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Particles production

Charged hadron (pions and protons) production Low pT – hydrodynamic Intermediate pT – partonic

coalescence High pT – jet fragmentation

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pQCD: Color charge and flavor dependence of parton energy loss

dE/dx(c/b)<dE/dx(uds)< dE/dx(g)

S. Wicks et al., NPA 784(2007)426

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X.N. Wang: PRC58(2321)1998.

Study the PID spectra and pbar/p ratios can help to further understand how the g/q jets interact with the medium

Parton energy loss in HIJING

HIJING calculation

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Different mechanisms govern hadron formation in the different kinematic region

Different hadron species may have different sources

Those sources (g/q) may have different behavior when propagating the medium

To study those behaviors,PID in large pT range is required!

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STAR detectors: TPC & TOFr

A new technology (TOF) ----Multi-gap Resistive Plate Chamber

1. Good timing resolution (<100ps)2. Two trays (TOFr+TOFp) for run 4,

acceptance~0.01, 120 trays (TOFr) in the future

Time Projection Chamber

1. Tracking2. Ionization energy loss (dE/dx)

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PID – Hadrons

TPC

Relativistic rising of dE/dx

High pT

High performance of time resolution

Low & intermediate pT2.5<pT<3.0

PID up to 12 GeV/c

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Pion & proton spectra

PID up to 12 GeV/c

STAR Collaboration PRL 97 (2006) 152301PAs: H. Liu, O. Barannikova, L. Ruan and Z. Xu

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Nuclear Modification factor

In central Au+Au collisions:

At 1.5<pT<7 GeV/c, RCP(p+pbar) > RCP() , RCP(p+pbar) shows obvious decreasing trend.

At 4<pT<12 GeV/c, both and p are strongly suppressed. They approach to each other at about 0.3

Curve:I. Vitev, PLB 639 (2006) 38.pT

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Color charge and flavor dependence of parton energy loss

High pT Rcp measurements: , p(pbar), e, , 0

pT

Nucl-ex/0607012 PRL 96 (2006) 202301

Rcp(RAA)~0.2 for all these particles!

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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, parton energy loss underpredicts the ratios (X.N. Wang, PRC 58 (2321) 1998).

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Proton over pion ratios

1. The p(pbar)/ ratios in Au+Au collisions show strong centrality dependence.

2. In central Au+Au collisions, the p(pbar)/ ratios reach maximum value at pT~2-3 GeV/c, approach the corresponding ratios in p+p, d+Au collisions at pT>5 GeV/c.

3. In general, parton energy loss models underpredict p/ ratios. R.J. Fries, et al., Phys. Rev. Lett. 90 202303 (2003); R. C. Hwa, et al., Phys. Rev. C 70, 024905 (2004); DELPHI Collaboration, Eur. Phy. J. C 5, 585 (1998), Eur. Phy. J. C 17, 207 (2000).

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B/M enhancement at intermediate pT

1) The relative baryon enhancement is clearly observed in the p/pi ratios at

intermediate pT, the similar behavior can also be seen in the /Ks0

ratios. At the same pT region, the NQ scaling of v2 has also been observed. This can

be explained by the parton coalescence phenomena.2) In general, parton energy loss models underpredict p/ ratios. R.J. Fries, et al., Phys. Rev. Lett. 90 202303 (2003); R. C. Hwa, et al., Phys. Rev. C 70, 024905 (2004); DELPHI Collaboration, Eur. Phy. J. C 5, 585 (1998), Eur. Phy. J. C 17, 207 (2000).

STAR Nucl-ex/0601042

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Summary

First time to extend PID pt range up to 12 GeV/c for charged pion, kaon and (anti-)proton

First time to observe the similar suppressions for high pt mesons and baryons, which challenges the standard parton energy loss model

Further test the coalescence model in the intermediate pt range

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