Partonic Collectivity at RHIC ShuSu Shi for the STAR collaboration Lawrence Berkeley National Laboratory Central China Normal University

DNP 2009, Oct , Hawaii2  Introduction  STAR Detectors  v 2 Results and Discussions  System size and Energy Dependence  Multi-strange Hadron  and Ω  Summary Outline

DNP 2009, Oct , Hawaii3 T < T conf T > T conf constant potential linear potential r V(r,T)  The potential between quarks is a function of distance. It also depends on the temperature.  At low temperature, the potential increases linearly with the distance between quarks  quarks are confined  At high temperature (RHIC), the confinement potential is ‘melted’  quarks are deconfined Introduction

DNP 2009, Oct , Hawaii4 Elliptic Flow (v 2 ) Coordinate-Space Anisotropy Momentum-Space Anisotropy  Strange hadron: less sensitive to late hadronic rescattering  Elliptic flow => Early stage collision dynamics  Good probe of the early stage of the collision partonic hadronic D , Ω, Ξ, Λ , K, p interactions

DNP 2009, Oct , Hawaii5 TPC dE/dx PID: pion/kaon: p T ~ 0.6 GeV/c; proton p T ~ 1.0 GeV/c STAR Detectors

DNP 2009, Oct , Hawaii6 6 Reconstructed by decay topology  Daughter hadrons are identified by dE/dx in TPC Signal to background ratio ~ 1 – 20 (depends on colliding system, particle type and p T ) Particle Identification STAR: preliminary

DNP 2009, Oct , Hawaii7 Participant Plane  RP: the reaction plane  Defined by the impact parameter  Initial geometry: ε std  PP: the participant plane  Defined by the major axis of the created system  Initial geometry: ε part  v 2 from the event plane method is sensitive to the participant plane PHOBOS : NPA774: 523 (2006), PRC77, (2008) S. A. Voloshin, A. M. Poskanzer, A.Tang and G.Wang, PLB, 659 (2008),

DNP 2009, Oct , Hawaii8 Ideal Hydro Test  Ideal hydro fails to reproduce centrality dependence of the data. Fluctuation of v 2 ? Viscosity? Incomplete thermalization? Ideal hydro: P. Huovinen, private communication

DNP 2009, Oct , Hawaii9 System and Energy Dependence Au+Au and Cu+Cu  Minimum bias events  200 and 62.4 GeV Event plane  Au+Au: TPC Systematic: FTPC, 5%  Cu+Cu: FTPC Systematic: v 2 {AA-pp}, 5% NQ scaling  De-confinement at RHIC  Partonic collectivity Scaled by eccentricity  Remove the initial geometry Stronger collective flow in larger system STAR: preliminary STAR Au + Au 62.4 GeV : PRC75, (2007) ε part {2}: J. Y. Ollitrault, A. M. Poskanzer and S. A. Voloshin, PRC80, (2009)

DNP 2009, Oct , Hawaii10 Centrality Dependence  Au+Au and Cu+Cu at 200 GeV  NQ scaling for each centrality bin => partonic collectivity  Collectivity: Driven by number of participants, NOT by eccentricity.  Larger v 2 /  part indicates stronger flow in more central collisions. Hint: the system created in collisions at RHIC is not fully thermalized. STAR: preliminary STAR Au + Au 200 GeV : PRC77, (2008) S. Voloshin, A. Poskanzer, PL B474, 27(00). D. Teaney, et. al., nucl-th/

DNP 2009, Oct , Hawaii11  Low p T (≤ 2 GeV/c): hydrodynamic mass ordering  High p T (> 2 GeV/c): number of quarks ordering  s-quark hadron: smaller interaction strength in hadronic medium  light- and s-quark hadrons: similar v 2 pattern => Collectivity developed at partonic stage! Partonic Collectivity PHENIX π and p : nucl-ex/ v1

DNP 2009, Oct , Hawaii12  The v 2 of the multi-strange hadrons ϕ, Ω  Partonic collectivity at RHIC!  The observed NQ scaling  De-confinement at RHIC! Test thermalization at RHIC Heavy flavor measurements  Thermalization at RHIC? Summary

DNP 2009, Oct , Hawaii13 Backup

DNP 2009, Oct , Hawaii14 Assume Borghini et al. Phys. Rev. C70 (2006)4905 KS0KS0 v 2 versus M inv method

DNP 2009, Oct , Hawaii15 Centrality Dependence STAR: preliminary STAR Au + Au 200 GeV : PRC77, (2008)

DNP 2009, Oct , Hawaii16 Ideal Hydro Test Ideal hydro: P. Huovinen, private communication  Ideal hydro fails to reproduce centrality dependence of the data. Fluctuation of v 2 ? Viscosity? Incomplete thermalization? Au+Au at 200 GeV STAR Au + Au 200 GeV : PRC77, (2008)