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Directed Flow from Au+Au Collisions at 200 GeV

Jiayun Chen

(for Collaboration)

Institute of Particle Physics, CCNU, Wuhan

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• Introduction and motivation• Date-set and Cuts• Directed flow results

– η dependence (proton, antiproton, pion)

– Excitation function• Summary

Jiayun Chen (2010 高能物理年会 ) 2

Outline

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Introduction

z

x • Directed flow (v1) , sensitive to earliest collision stage (b > 0)

– pre-equilibrium at forward rapidity, at mid-rapidity perhaps different origin

• peripheral collisions produce an asymmetric particle source in coordinate space

1 cosv

• spatial anisotropy momentum anisotropy

• sensitive to the EoS

xy

z

z

x

Jiayun Chen (2010 高能物理年会 )

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Anti-flow/3rd flow component

flowantiflow

Directed flow (v1) and phase transition,QGP v1(y) flat at mid-rapidity

J. Brachmann, S. Soff, A. Dumitru, H. Stöcker, J. A. Maruhn, W. Greiner, L. V. Bravina, D. H. Rischke, PRC 61 (2000), 024909.

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Baryon stopping and space-momentum correlation

R. Snellings, H. Sorge, S. Voloshin, F. Wang, N. Xu, PRL 84 (2000), 2803.

space-momentum correlations, nucleus stoppingwiggle structure of v1(y) develops

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STAR detector

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Data-set and cuts

Tracks used for TPC : No. of fit hits [15, 50]∈Global DCA [0.0, 2.0]∈

No. of fit hits/No.of possible hits ∈[0.52, 1.05]

0.1 < pT < 12.0 GeV/c | η | < 1.3η Symmetry [- 3.0, 3.0]∈

Tracks used for FTPC:No. of fit hits [5, 11]∈Global DCA [0.0, 2.0]∈

No. of fit hits/No. of possible hits > 0.52

0.1 < pT < 8.0 GeV/c 2.5< | η | < 4.0η Symmetry [- 5.0, 5.0]∈

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Charged hadron v1

System-size independence was observed for charged hadron v1. Phys. Rev. Lett. 101, 252301 (2008)

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Pion v1 at RHIC

Phys. Rev. Lett. 84 (2000) 2803;Phys. Lett. B 526 (2002) 309;Phys. Rev. C 71 (2005) 054905;Phys. Rev. C 81, 014904 (2010).

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PID v1 at RHIC

Sizable difference between v1 of protons and anti-protons in mid-central collisions

Negative v1 slope for protons is observed in 30-80% centralities.

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PID v1 at RHIC

•The anti-flow has difficulties in explaining the centrality dependence of v1.•The observed v1 for protons is a convolution of directed flow of produced protons with that of transported protons.

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NA49 : C. Alt et al., Phys. Rev. C 68 (2003) 034903E895 : H. Liu et al., Phys. Rev. Lett. 84 (2000) 5488

Proton v1 excitation function

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• Directed flow for pions, anti-protons are found to have negative slope.

• Protons exhibit a flat shape around mid-rapidity. Sizable difference is seen between v1 of protons and anti-protons in 5-30% central collisions.

• Anti-flow can explain the negative slope, however, it has difficulties explaining the centrality dependence of the slope.

• Call for theoretical input to describe the data.

Jiayun Chen (2010 高能物理年会 ) 13

Summary

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Back-up slides

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resolution