Directed Flow from Au+Au Collisions at 200 GeV
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Transcript of Directed Flow from Au+Au Collisions at 200 GeV
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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
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Outline
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Introduction
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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
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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.
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Summary
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Back-up slides
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resolution