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Strange Hadron Elliptic Flow at STAR

Strange Hadron Elliptic Flow at STAR. Yan Lu Uni. of Science and Technology of China. STAR Asian meeting, Pusan Uni., May 6-10, 2009. Outline. Introduction and motivation Elliptic flow Strange hadron We learned from published data Experiments

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Strange Hadron Elliptic Flow at STAR

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  1. Strange Hadron Elliptic Flow at STAR Yan Lu Uni. of Science and Technology of China STAR Asian meeting, Pusan Uni., May 6-10, 2009

  2. Outline • Introduction and motivation Elliptic flow Strange hadron We learned from published data • Experiments • Results and discussions System size and centrality dependence Ideal hydrodynamic limit with transport model approach • Summary STAR regional meeting, 2009 May 6-9., Pusan Uni.

  3. Anisotropy Parameter v2 coordinate-space-anisotropy  momentum-space-anisotropy y py px x Sensitive to the early stage!

  4. Flow of Strange Hadrons (GeV) • freeze-out of multi-strange hadrons - at higher temperature Tfo - with lower collective velocity T • small cross section of strange hadrons with non-strange hadrons • sensitivity to the early, partonic stage STAR: Nucl. Phys. A715, 458c (2003) Phys. Rev. Lett. 92, 112301 (2004) Phys. Rev. Lett.92, 182301 (2004) STAR regional meeting, 2009 May 6-9., Pusan Uni.

  5. Little History for Dataset STAR data available for strange hadron elliptic flow analysis Published: 130 GeV Au+Au Run I 200 GeV Au+Au Run II (2M, minibias) 62.4 GeV Au+Au Run IV (6.2M) 200 GeV Au+Au Run IV (20M, centrality dependence ) More data: 200 GeV Cu+Cu Run V (24M) 62.4 GeV Cu+Cu Run V (12.5M) 200 GeV Au+Au Run VII (60M, phi and Omega) STAR regional meeting, 2009 May 6-9., Pusan Uni.

  6. We learned from minibias H. Masui, ATHIC2008 • Mass ordering of v2 • collective flow • Sizable v2 for multi-strange hadrons • small hadronic cross section • Number of Quark (NQ) scaling • vs (mT - mass)/nq • Partonic collectivity • Deconfinement PHENIX: Phys. Rev. Lett. 98, 162301 (2007) STAR: Phys. Rev. Lett. 99, 112301 (2007), Phys. Rev. C77, 054901 (2008) Hydro results: Pasi Huovinen, private communication; P. Huovinen and P. V. Ruuskanen, Annu. Rev. Nucl. Part. Sci. 56, 133 (2006) STAR regional meeting, 2009 May 6-9., Pusan Uni. 6

  7. Motivation of Systematic Study Beam energy System size Centrality - Systematic study will gain information on interplay of collectivity, deconfinement and thermalization as a function of beam energy and collision centralities. - Determine parameters for partonic EoS. STAR regional meeting, 2009 May 6-9., Pusan Uni.

  8. Centrality dependence Phys. Rev. C77, 054901 (2008) 200 GeV Au+Au • Scale by eccentricity to remove initial geometry effect. • For a given centrality bin, a scaling with mT-m and nq. • Larger v2/(nqpart) indicates stronger partonic flow in more central collisions. STAR regional meeting, 2009 May 6-9., Pusan Uni.

  9. Energy dependence Phys. Rev. C77, 054901 (2008) • Partonic collectivity and deconfinement at 62.4 GeV Au+Au • Similar centrality dependence for 62.4 GeV and 200 GeV. Yan Lu STAR regional meeting, 2009 May 6-9., Pusan Uni.

  10. Thermalization? In case of thermalization:  e v2 Phys. Rev. C77, 054901 (2008) Low density limit: 1 dN  e v 2 S dy 2 part is for the participant zone. S. Voloshin, A. Poskanzer, PLB 474, 27, 2000. Data: S. Voloshin, nucl-ex/ 0701038 Hydro: Kolb, Sollfrank, Heinz, PRC 62 (2000) 054909 • Thermalization only possible for most central collisions. STAR regional meeting, 2009 May 6-9., Pusan Uni. Yan Lu

  11. Move to new data for analysis STAR regional meeting, 2009 May 6-9., Pusan Uni.

  12. Experiments • Large acceptance • Main TPC; |η| < 1, full azimuth • Au + Au at 200 GeV • 60 M events • Centrality: 0 - 80 % • Cu + Cu at 200 GeV • 24 M events • Centrality: 0 - 60 % • 0 - 20 and 20 - 60 % • Cu + Cu at 62.4 GeV • 12.5 M events • Centrality: 0 - 60 % • Event plane • TPC: Au + Au collisions • Systematic errors: FTPC • Forward TPC: Cu + Cu collisions • 2.5 < |η| < 4 • Rapidity gap could reduce “non-flow” effects significantly in Cu + Cu collisions STAR preliminary STAR regional meeting, 2009 May 6-9., Pusan Uni. Yan Lu

  13. Particle identification • Reconstructed by weak decay topology • Daughter hadrons are identified by dE/dx in TPC • Signal to background ratio ~ 3 - 20 STAR regional meeting, 2009 May 6-9., Pusan Uni. Yan Lu

  14. Test hydro in smaller system Ideal hydro: P. Huovinen, private communication STAR preliminary • pT < 2 GeV/c • Smaller v2 for heavier hadrons as expected from Hydrodynamics. • pT > 2 GeV/c • Sizable v2(Ξ) even in small system. • Ideal hydro fails to reproduce centrality dependence • Fluctuation of v2? • Viscosity ? • Incomplete thermalization ? STAR regional meeting, 2009 May 6-9., Pusan Uni. Yan Lu

  15. Number-of-quark scaling • Number of Quark (NCQ) scaling works well in all centrality bins • Partonic flow ! D. Molnar and S. Voloshin, PRL91, 092301 (2003) R. J. Fries et. al., PRC68, 044902 (2003) V. Greco et. al, PRC68, 034904 (2003) J. Jia and C. Zhang, PRC75, 031901(R) (2007)... STAR regional meeting, 2009 May 6-9., Pusan Uni. 15

  16. Energy dependence • v2 in Cu + Cu (Au +Au) at 200 and 62.4 GeV are comparable within statistical errors v2 at Cu + Cu 62.4 GeV ~ 12.5 M events - Same procedure used for 200 GeV. - Event plane resolution is 0.088 ± 0.004 in 0 - 60 %, about factor 2 smaller than that in 200 GeV due to lower multiplicity. STAR Au + Au 200 GeV : PRC77, 054901 (2008) Au + Au 62.4 GeV : PRC75, 054906 (2007) STAR regional meeting, 2009 May 6-9., Pusan Uni. 16

  17. System Size Dependence I • Stronger collective flow in Au+Au than Cu+Cu Au + Au : PRC77, 054901 (2008) STAR regional meeting, 2009 May 6-9., Pusan Uni. 17

  18. System Size Dependence II STAR preliminary Au + Au : PRC77, 054901 (2008) • v2 seems solely depending on initial geometry and number of participant in 200 GeV collisions • v2∝ v2(ε, Npart) STAR regional meeting, 2009 May 6-9., Pusan Uni. 18

  19. Run VII  and  PHENIX π and p: nucl-ex/0604011v1 NQ inspired fit: X. Dong et al. Phy. Let. B 597 (2004) 328-332 Final word on partonic collectivity at RHIC! STAR regional meeting, 2009 May 6-9., Pusan Uni. 19

  20. Ideal Hydrodynamical Limit hydro limit • Knudsen number • degrees of equilibration • Reach hydro limit when K -> 0 • Transport model results (symbols) can be reproduced by the formula below • K0 = 0.7, cs2 = 1/3 v2 Knudsen number K C. Gombeaud and J.-Y. Ollitrault, PRC77, 054904 (2008) σ : parton cross section cs : speed of sound S : transverse area (obtained by Glauber MC) STAR regional meeting, 2009 May 6-9., Pusan Uni. 20

  21. STAR preliminary STAR preliminary ΞΛp K π Ideal Hydro Limit • Ideal Hydro Limit • Event in central Au + Au collisions, fitting results indicate that the system is still away from hydro limit PHENIX π, K and p: nucl-ex/0604011v1 CGC eccentricity: H.J. Drescher and Y. Nara, PRC 76 041903 (2007), H.J. Drescher and Y.Nara, PRC 75 034905 (2007) STAR regional meeting, 2009 May 6-9., Pusan Uni. 21

  22. Summary • Elliptic flow (v2) for K0S, Λ and Ξ have been measured in Cu + Cu 200 GeV at STAR • Number of Quark (NQ) scaling of v2 • Strange hadrons follow the NQ scaling in Cu + Cu • Centrality dependence of v2/ε in Au + Au & Cu + Cu 200 GeV • Stronger collective flow for more central collisions • Transport model fit with finite Knudsen number • Hydrodynamic limit has not been reached at RHIC within the transport model approach Beam energy scan STAR regional meeting, 2009 May 6-9., Pusan Uni. 22

  23. Thanks! STAR regional meeting, 2009 May 6-9., Pusan Uni. 23

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