Directed Flow from AuAu Collisions at 200 Ge

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

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

Introduction y x z • peripheral collisions produce an asymmetric particle source in coordinate space • spatial anisotropy ® momentum anisotropy • sensitive to the Eo. S • Directed flow (v 1) , sensitive to earliest collision stage (b > 0) x z – pre-equilibrium at forward rapidity, at midrapidity perhaps different origin Jiayun Chen (2010 高能物理年会) 3

Anti-flow/3 rd flow component flow antiflow Directed flow (v 1) and phase transition, QGP v 1(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) 4

Baryon stopping and spacemomentum correlation space-momentum correlations, nucleus stopping wiggle structure of v 1(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) 5

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

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 < p. T < 12. 0 Ge. V/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 < p. T < 8. 0 Ge. V/c 2. 5< | η | < 4. 0 η Symmetry ∈[- 5. 0, 5. 0] Jiayun Chen (2010 高能物理年会) 7

Charged hadron v 1 Phys. Rev. Lett. 101, 252301 (2008) System-size independence was observed for charged hadron v 1. Jiayun Chen (2010 高能物理年会) 8

Pion v 1 at RHIC Phys. Rev. Lett. 84 (2000) 2803; Phys. Lett. B 526 (2002) 309; Phys. Rev. C 71 (2005) 054905; Jiayun Chen (2010 高能物理年会) Phys. Rev. C 81, 014904 (2010). 9

PID v 1 at RHIC Sizable difference between v 1 of Negative v 1 slope for protons is protons and anti-protons in midobserved in 30 -80% centralities. central collisions Jiayun Chen (2010 高能物理年会) 10

PID v 1 at RHIC • The anti-flow has difficulties in explaining the centrality dependence of v 1. • The observed v 1 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) 11

Proton v 1 excitation function NA 49 : C. Alt et al. , Phys. Rev. C 68 (2003) 034903 E 895 : H. Liu et al. , Phys. Rev. Lett. 84 (2000) 5488 Jiayun Chen (2010 高能物理年会) 12

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 v 1 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

Back-up slides 14

resolution 15