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Partonic Collectivity at RHIC

Partonic Collectivity at RHIC. ShuSu Shi for the STAR collaboration Lawrence Berkeley National Laboratory Central China Normal University. Outline. Introduction STAR Detectors v 2 Results and Discussions System size and Energy Dependence Multi-strange Hadron  and Ω

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Partonic Collectivity at RHIC

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

  2. Outline • Introduction • STAR Detectors • v2 Results and Discussions • System size and Energy Dependence • Multi-strange Hadron andΩ • Summary

  3. Introduction 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 T < T conf linear potential constant potential T > T conf r

  4. Elliptic Flow (v2) hadronic partonic Coordinate-Space Anisotropy Momentum-Space Anisotropy interactions • Strange hadron: less sensitive to late hadronic rescattering • Elliptic flow => • Early stage collision dynamics • Good probe of the early stage of the collision , Ω, Ξ, Λ D , K, p

  5. STAR Detectors TPC dE/dx PID: pion/kaon: pT ~ 0.6 GeV/c; proton pT ~ 1.0 GeV/c

  6. Particle Identification • 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 pT) STAR: preliminary

  7. Participant Plane • RP: the reaction plane • Defined by the impact parameter • Initial geometry: εstd • PP: the participant plane • Defined by the major axis of the created system • Initial geometry: εpart PHOBOS : NPA774: 523 (2006), PRC77, 014906 (2008) S. A. Voloshin, A. M. Poskanzer, A.Tang and G.Wang, PLB, 659 (2008), 537-541 • v2 from the event plane method is sensitive to the participant plane

  8. Ideal Hydro Test Ideal hydro: P. Huovinen, private communication • Ideal hydro fails to reproduce centrality dependence of the data. • Fluctuation of v2? Viscosity? Incomplete thermalization?

  9. 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: v2{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, 054906 (2007) εpart{2}: J. Y. Ollitrault, A. M. Poskanzer and S. A. Voloshin, PRC80, 014904 (2009)

  10. Centrality Dependence STAR Au + Au 200 GeV : PRC77, 054901 (2008) STAR: preliminary S. Voloshin, A. Poskanzer, PL B474, 27(00). D. Teaney, et. al., nucl-th/0110037 • 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 v2/part indicates stronger flow in more central collisions. • Hint: the system created in collisions at RHIC is not fully thermalized.

  11. Partonic Collectivity PHENIX πand p: nucl-ex/0604011v1 • Low pT (≤ 2 GeV/c): hydrodynamic mass ordering • High pT (> 2 GeV/c): number of quarks ordering • s-quark hadron: smaller interaction strength in hadronic medium • light- and s-quark hadrons: similar v2 pattern • => Collectivity developed at partonic stage!

  12. Summary • The v2 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?

  13. Backup

  14. v2 versus Minv method KS0 Assume Borghini et al. Phys. Rev. C70 (2006)4905

  15. Centrality Dependence STAR: preliminary STAR Au + Au 200 GeV : PRC77, 054901 (2008)

  16. Ideal Hydro Test Ideal hydro: P. Huovinen, private communication Au+Au at 200 GeV STAR Au + Au 200 GeV : PRC77, 054901 (2008) • Ideal hydro fails to reproduce centrality dependence of the data. • Fluctuation of v2? Viscosity? Incomplete thermalization?

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