Anisotropic Flow at RHIC Jiayun Chen (for Collaboration) Institute of Particle Physics, HZNU, Wuhan, , P.R.China Brookhaven National Lab, Upton, NY,11973, USA
Jiayun Chen for STAR Collaboration – QNP Outline Introduction and Motivation STAR Experiment Result and discussions Partonic Collectivity Ideal Hydrodynamic Indentified Particles’ (PID) Directed Flow Summary and outlook
Jiayun Chen for STAR Collaboration – QNP This is believed to be due to pressure gradients in the dense medium which lead to collective motion. Directed flow (v 1 ) at forward rapidities describes the “side-splash”, the foremost early collective motion of the system; Elliptic flow (v 2 ) demonstrated the development of collectivity Provide insights into the EOS. Coordinate-Space Anisotropy Momentum-Space Anisotropy interactions pressure gradient collective flow Azimuthal Anisotropy
Jiayun Chen for STAR Collaboration – QNP STAR Detector 2.5<|η|<4.0 |η|<1.5 ZDC-SMD
Jiayun Chen for STAR Collaboration – QNP Partonic Collectivity 1)At low p T - mass dependence 2)At intermediate p T - clear difference between baryons and mesons 3) Hadrons with u-, d-, s-quarks show similar collectivity Final word on partonic collectivity at RHIC! PHENIX π and p: nucl-ex/ v1 NQ inspired fit: X. Dong et al. Phy. Let. B 597 (2004)
Jiayun Chen for STAR Collaboration – QNP STAR preliminary Ideal Hydro Test (1) Ideal hydro: P. Huovinen, private communication Ideal hydro fails to reproduce the data. Fluctuation of v 2 ? Viscosity ? Incomplete thermalization ? Au+Au at 200 GeV Phys. Rev. C 77 (2008) 54901
Jiayun Chen for STAR Collaboration – QNP Ideal Hydro Test (2) v 4 /v 2 2 results suggest that ideal hydro limit is not reached. Borghini & Ollitrault, PLB (2006) Au+Au at 200 GeV 0-80%
Jiayun Chen for STAR Collaboration – QNP Stopping and space-momentum correlation R. Snellings, H. Sorge, S. Voloshin, F. Wang, N. Xu, PRL 84 (2000), space-momentum correlations, nucleus stopping wiggle structure of v 1 (y) develops
Jiayun Chen for STAR Collaboration – QNP Anti-flow/3rd flow component flow antiflow Directed flow (v 1 ) and phase transition,QGP v 1 (y) flat at mid-rapidity Phys. Rev. C 61 (2000),
Jiayun Chen for STAR Collaboration – QNP PID Directed Flow v 1 First measurement of directed flow of antiprotons. Proton directed flow "collapses". Antiproton v 1 has the same sign of that of pions - the collapse of proton v 1 is not a mass effect. Kaon has a smaller k/p cross section than that of pions, thus it suffers less shadowing effect, yet we found negative v 1 slope for both charged kaon and kshort- consistent with "anti-flow" picture. Proton 0.4<p T <1.0 (GeV/c) Antiproton 0.4<p T <1.0 (GeV/c) Pion 0.15<p T <0.75 (GeV/c) Kaon 0.2<p T <0.6 (GeV/c) STAR preliminary
Jiayun Chen for STAR Collaboration – QNP Directed Flow v 1 Proton v 1 slope is close to zero, if compared to others. The models with shadowing effects (RQMD) cannot explain the v 1 slope relative to that of pions. Phys. Rev. Lett. 84 (2000) 2803; Phys. Lett. B 526 (2002) 309–314; Phys. Rev. C 71, (2005). STAR preliminary
Jiayun Chen for STAR Collaboration – QNP Charged hadrons Directed Flow v 1 At mid-rapidity, all the results have comparable values. At forward rapidity, the trend of v 1 from low energy is different from high energies. This is due to early longitudinal collision dynamics. V 1 values lie on a common trend. STAR : PRL 92 (2004) PRL101 ( 2008 ) NA49: PRC68(2003) STAR Preliminary
Jiayun Chen for STAR Collaboration – QNP Summary We found that proton v 1 is "collapsed". By comparing to anti-proton v 1, such collapse is found not due to mass effect. The comparison of the ratio of proton v 1 to that of pions, shows that the shadowing effect alone cannot explain the collapse of proton v 1. Our finding is consistent with “anti-flow” phenomena. V 1 results from 9.2GeV are similar to those obtained at SPS from collisions at similar energies Partonic collectivity at RHIC done! Test of local thermalization is the next step. Ideal hydro limit: v 4 /v 2 2 data larger than ideal hydro prediction.