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Directed Flow for Au+Au Collisions at STAR

Directed Flow for Au+Au Collisions at STAR. 十三届全国中高能核物理大会暨第七届全国中高能核物理专题研讨会. Jiayun Chen ( 陈佳赟 ) (for Collaboration) Institute of Particle Physics, HZNU , Wuhan, 430079, P.R.China. Outline. Introduction and Motivation STAR Experiment Result and discussions

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Directed Flow for Au+Au Collisions at STAR

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  1. Directed Flow for Au+Au Collisions at STAR 十三届全国中高能核物理大会暨第七届全国中高能核物理专题研讨会 Jiayun Chen (陈佳赟) (for Collaboration) Institute of Particle Physics, HZNU, Wuhan, 430079, P.R.China

  2. Outline • Introduction and Motivation • STAR Experiment • Result and discussions • Indentified Particles’ (PID) Directed Flow from 200GeV • Charged hadron’s Directed Flow from 9.2GeV • Summary and outlook 2009.11.5-2009.11.7. USTC

  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 Azimuthal Anisotropy • Directed flow (v1) , sensitive to earliest collision stage (b > 0) • pre-equilibrium at forward rapidity, at mid-rapidity perhaps different origin 2009.11.5-2009.11.7. USTC

  4. 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. 2009.11.5-2009.11.7. USTC

  5. 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. 2009.11.5-2009.11.7. USTC

  6. STAR Detector |η|<1.5 ZDC-SMD 2.5<|η|<4.0 2009.11.5-2009.11.7. USTC

  7. 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) 2009.11.5-2009.11.7. USTC

  8. Pion’s Directed Flow v1 • Pion’s directed flow compare with RQMD, UrQMD, AMPT and QGSM model. • After scaling by the factor, the pion v1 from UrQMD and QGSM model seems have the same trend with the data. Phys. Rev. Lett. 84 (2000) 2803; Phys. Lett. B 526 (2002) 309–314; Phys. Rev. C 71, 054905 (2005); arXiv:0910.1400v2 2009.11.5-2009.11.7. USTC

  9. Ratio of Directed Flow v1 Slope • 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); arXiv:0910.1400v2. 2009.11.5-2009.11.7. USTC

  10. 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. Charged hadrons Directed Flow v1 STAR Preliminary STAR Preliminary STAR : PRL 92 (2004) 062301 PRL101（2008）252301 NA49: PRC68(2003)034903 2009.11.5-2009.11.7. USTC

  11. 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. 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. V1 results from 9.2GeV are similar to those obtained at SPS from collisions at similar energies. Summary 2009.11.5-2009.11.7. USTC

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