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Anisotropic Flow at RHIC

Anisotropic Flow at RHIC. Jiayun Chen (for Collaboration) Institute of Particle Physics, HZNU, Wuhan, 430079, P.R.China Brookhaven National Lab, Upton, NY,11973, USA. Outline. Introduction and Motivation STAR Experiment Result and discussions Partonic Collectivity

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Anisotropic Flow at RHIC

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  1. Anisotropic Flow at RHIC Jiayun Chen (for Collaboration) Institute of Particle Physics, HZNU, Wuhan, 430079, P.R.China Brookhaven National Lab, Upton, NY,11973, USA

  2. 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 – QNP2009

  3. Azimuthal Anisotropy Coordinate-Space Anisotropy Momentum-Space Anisotropy interactions pressure gradient  collective flow • This is believed to be due to pressure gradients in the dense medium which lead to collective motion. • Directed flow (v1) at forward rapidities describes the “side-splash”, the foremost early collective motion of the system; • Elliptic flow (v2) demonstrated the development of collectivity • Provide insights into the EOS. Jiayun Chen for STAR Collaboration – QNP2009

  4. STAR Detector |η|<1.5 ZDC-SMD 2.5<|η|<4.0 Jiayun Chen for STAR Collaboration – QNP2009

  5. Partonic Collectivity • At low pT - mass dependence • At intermediate pT - 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/0604011v1 NQ inspired fit: X. Dong et al. Phy. Let. B 597 (2004) 328-332 Jiayun Chen for STAR Collaboration – QNP2009

  6. Ideal Hydro Test (1) Ideal hydro: P. Huovinen, private communication Au+Au at 200 GeV STAR preliminary Phys. Rev. C 77 (2008) 54901 • Ideal hydro fails to reproduce the data. • Fluctuation of v2? Viscosity ? Incomplete thermalization ? Jiayun Chen for STAR Collaboration – QNP2009

  7. Ideal Hydro Test (2) Au+Au at 200 GeV 0-80% Borghini & Ollitrault, PLB 642 227 (2006) • v4/v22 results suggest that ideal hydro limit is not reached. Jiayun Chen for STAR Collaboration – QNP2009

  8. 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 for STAR Collaboration – QNP2009

  9. flow antiflow Anti-flow/3rd flow component Directed flow (v1) and phase transition,QGP  v1(y) flat at mid-rapidity Phys. Rev. C 61 (2000), 024909. Jiayun Chen for STAR Collaboration – QNP2009

  10. PID Directed Flowv1 • First measurement of directed flow of antiprotons. • Proton directed flow "collapses". • Antiproton v1 has the same sign of that of pions - the collapse of proton v1 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 v1 slope for both charged kaon and kshort- consistent with "anti-flow" picture. STAR preliminary STAR preliminary Proton 0.4<pT<1.0 (GeV/c) Antiproton 0.4<pT<1.0 (GeV/c) Pion 0.15<pT<0.75 (GeV/c) Kaon 0.2<pT<0.6 (GeV/c) Jiayun Chen for STAR Collaboration – QNP2009

  11. Directed Flow v1 • Proton v1 slope is close to zero, if compared to others. • The models with shadowing effects (RQMD) cannot explain the v1 slope relative to that of pions. STAR preliminary Phys. Rev. Lett. 84 (2000) 2803; Phys. Lett. B 526 (2002) 309–314; Phys. Rev. C 71, 054905 (2005). Jiayun Chen for STAR Collaboration – QNP2009

  12. Charged hadrons Directed Flow v1 At mid-rapidity, all the results have comparable values. At forward rapidity, the trend of v1 from low energy is different from high energies. This is due to early longitudinal collision dynamics. V1 values lie on a common trend. STAR Preliminary STAR Preliminary STAR : PRL 92 (2004) 062301 PRL101（2008）252301 NA49: PRC68(2003)034903 Jiayun Chen for STAR Collaboration – QNP2009

  13. Summary We found that proton v1 is "collapsed". By comparing to anti-proton v1, such collapse is found not due to mass effect. The comparison of the ratio of proton v1 to that of pions, shows that the shadowing effect alone cannot explain the collapse of proton v1. Our finding is consistent with “anti-flow” phenomena. V1 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: v4/v22 data larger than ideal hydro prediction. Jiayun Chen for STAR Collaboration – QNP2009

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