1. Directed Flow from Au+Au Collisions at 200 GeV
Jiayun Chen
(for Collaboration)
Institute of Particle Physics, CCNU, Wuhan

2. Outline 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

3. Directed flow (v1) , sensitive to earliest collision stage (b > 0)
Introduction
peripheral collisions produce an asymmetric particle source in coordinate space
spatial
anisotropy
momentum
sensitive to the EoS x y z z x
Directed flow (v1) , sensitive to earliest collision stage (b > 0)
pre-equilibrium at forward rapidity, at mid-rapidity perhaps different origin
Jiayun Chen (2010 高能物理年会)

4. Anti-flow/3rd flow component
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),
Jiayun Chen (2010 高能物理年会)

5. Baryon stopping and space-momentum correlation
space-momentum correlations, nucleus stopping
wiggle structure of v1(y) develops
R. Snellings, H. Sorge, S. Voloshin, F. Wang, N. Xu, PRL 84 (2000), 2803.
Jiayun Chen (2010 高能物理年会)

6. STAR detector
Jiayun Chen (2010 高能物理年会)

7. Data-set and cuts η Symmetry ∈[- 3.0, 3.0] 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 | < 1.3
η 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 < | η | < 4.0
η Symmetry ∈[- 5.0, 5.0]
Jiayun Chen (2010 高能物理年会)

8. System-size independence was observed for charged hadron v1.
Phys. Rev. Lett. 101, (2008)
System-size independence was observed for charged hadron v1.
Jiayun Chen (2010 高能物理年会)

9. Pion v1 at RHIC Phys. Rev. Lett. 84 (2000) 2803;
Phys. Lett. B 526 (2002) 309;
Phys. Rev. C 71 (2005) ;
Phys. Rev. C 81, (2010).
Jiayun Chen (2010 高能物理年会)

10. 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.
Jiayun Chen (2010 高能物理年会)

11. 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.
Jiayun Chen (2010 高能物理年会)

12. Proton v1 excitation function
NA49 : C. Alt et al., Phys. Rev. C 68 (2003)
E895 : H. Liu et al., Phys. Rev. Lett. 84 (2000) 5488
Jiayun Chen (2010 高能物理年会)

13. Summary
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)

14. Back-up slides

15. resolution