Directed Flow from Au+Au Collisions at 200 GeV

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

2. Outline 2 • Introduction and motivation • Date-set and Cuts • Directed flow results • ηdependence (proton, antiproton, pion) • Excitation function • Summary Jiayun Chen (2010 高能物理年会)

3. y x z • spatial • anisotropy • momentum anisotropy • sensitive to the EoS x z • peripheral collisions produce an asymmetric particle source in coordinate space x z Introduction • 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 flow antiflow 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. 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 Tracks used forTPC: 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 2.5< |η| < 4.0 η Symmetry ∈[- 5.0, 5.0] Jiayun Chen (2010 高能物理年会)

8. Charged hadron v1 Phys. Rev. Lett. 101, 252301 (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) 054905; Phys. Rev. C 81, 014904 (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) 034903 E895 : H. Liu et al., Phys. Rev. Lett. 84 (2000) 5488 Jiayun Chen (2010 高能物理年会)

13. Summary Jiayun Chen (2010 高能物理年会) • 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.

14. Back-up slides

15. resolution