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Yan Lu for STAR collaboration Department of Modern Physics

System Size Dependence of Strange Hadron Elliptic Flow from 200 GeV Au + Au and Cu + Cu collisions. Yan Lu for STAR collaboration Department of Modern Physics University of Science and Technology of China. Quark Matter 2008 The 20 th International Conference on

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Yan Lu for STAR collaboration Department of Modern Physics

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  1. System Size Dependence of Strange Hadron Elliptic Flow from 200 GeV Au + Au and Cu + Cu collisions Yan Lu for STAR collaboration Department of Modern Physics University of Science and Technology of China Quark Matter 2008 The 20th International Conference on Ultra-relativistic Nucleus-Nucleus Collisions February 4–10, Jaipur, India

  2. Outline • Motivation • Data analysis • Results and Discussion • Summary and Outlook Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  3. Low density limit: 1 dN  e v 2 S dy In case of thermalization:  e v2 2 part is for the participant zone. Thermalization? ‘We argue that the centrality dependence of elliptic flow should be a good indicator of the degree of equilibration reached in the action. ’ S. Voloshin, A. Poskanzer, PLB 474, 27, 2000. Data: S. Voloshin, nucl-ex/ 0701038 Hydro: Kolb, Sollfrank, Heinz, PRC 62 (2000) 054909 • Possible thermalization only for the most central collisions. Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  4. Partonic Collectivity at RHIC minimum bias ‘They are made via coalescence of seemingly thermalized quarks in central Au+Au collisions, the observations imply hot and dense matter with partonic collectivity has been formed at RHIC’ STAR: Phys. Rev. Lett., 99, 112301(07), nucl-ex/0703033 Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  5. Collectivity nq scaling Local Thermalization  Why System Size and Centrality Dependence? • versus • - Systematic study for identified hadrons will gain information on interplay of collectivity, NQ scaling and thermalization as a function of collision system size and centrality. • Determine parameters for partonic EoS. Centrality System Size Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  6. System: Au+Au collision • Energy : sNN = 200 GeV • Event sample: ~22 M events • Centrality: 0 – 80 %, 0 – 10%, 10 – 40%, 40 – 80% • System: Cu+Cu collision • Energy : sNN = 200 GeV • Event sample: ~21 M events • Centrality: 0 – 60 %, 0 – 20%, 20 – 60% Dataset and Cuts multiplicity collision centrality • Event cuts: |Vertex z| < 30cm • FTPC track cuts: 6 =< nFitHits < 12, nHitsFit/nHitsPoss > 0.52 • pT > 0.1, 2.5 < || < 4.0, Dca < 2.0 cm Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  7. PID and v2 Methods • v2 vs. minv method (background subtraction technique): - used for K0S, Λ, Ξ, , and  analysis and for Au+Au and Cu+Cu datasets • flow method - Event Plane method used for Au+Au and Cu+Cu datasets - non-flow systematic: Lee-Yang Zero method for Au+Au and Event Plane method with FTPC reaction plane for Cu+Cu Lee-Yang Zero method: R. S. Bhalerao, N. Borghini, J.-Y.Ollitrault, Nucl. Phy. A 727 (2003) 373-426 Event Plane method: A. M. Poskanzer, S. A. Voloshin, Phys. Rev. C58, 1671 (1998) Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  8. Transverse kinetic energy: mT – m = (pT)2 + m2 - m Centrality Dependence ofIdentified v2 STAR Preliminary Transverse momentum 200 GeV Au+Au • All centralities: mass ordering at low pTmT-m scaling at low mT-m. • All centralities: baryon v2 > meson v2 at intermediate pT or mT-m. Hydro: P. Huovinen, private communications, 2007 Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  9. Centrality Dependence of Number-of-Quark Scaling nq: number of quark within a hadron STAR Preliminary 200 GeV Au+Au • nq scaling is observed at all centrality bins. Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  10. (c) Eccentricity Scaling(?) 200 GeV Au+Au 200 GeV Au+Au • Not observe the part scaling claimed by PHENIX. • Divided v2 by <v2>ch instead of part, it appears that the scaling works better. • Scale by part to remove initial geometry effect. • Larger v2/part indicates stronger flow in more central collisions. STAR Preliminary PHENIX: Phys. Rev. Lett 98, 162301 (2007) Phys. Lett. B 503, 58 (2001) Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  11.   p   pT-integrated v2/part STAR Preliminary • v2/part versus Npart  data: increasing trend indicates stronger flow in more central collisions.  hydro: little sensitivity to the collision centrality as expected in equilibrium scenario. • v2/part for a given centrality  hydro: a clear hadron mass dependence.  data: not clear due to large errors. • Above Npart ~ 170, integrated v2 consistent with hydro prediction indicates local thermalization. 200 GeV Au+Au Charge particle data: STAR, Phys. Rev. C 72, 014904, 2005. Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  12. System Size Dependence STAR Preliminary PHENIX: Phys. Rev. Lett 98, 162301 (2007) See S. S. Shi’s poster • A given colliding system: clear scaling with nq. • System size dependence: - No part scaling claimed by PHENIX - v2 seems to fall at lower pT in Cu+Cu than in Au+Au Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  13. Summary • We report azimuthal anisotropy parameter v2 of strange and multi-strange hadrons from Au+Au and Cu+Cu collisions at 200 GeV. Detailed centrality dependence is presented up to pT ~ 6 GeV/c. • At low pT region, collectivity is observed at all centrality bins under study.  it follows a mT-m scaling. • Not observe the part scaling. larger v2/part indicatesstronger flow in more central collisions and larger system. • v2/part increase with Npart, reaching hydro prediction in central Au+Au collisions. indicate thermalization in central Au+Au collisions. Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  14. Future: More systematic measurements for , : partonic EoS parameters Heavy quark collectivity: early thermalization of light quarks

  15. Backup slides! Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  16. y py px x y z x Reaction plane: z-x plane Elliptic flow beam impact parameter Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  17. v2 vs minv method SIG + BG • analysis method: v2 vs. minv • motivated by Borghini et al. [nucl-th/0407041] • advantages over standard method: • only one fit per pT bin - smaller systematic uncertainties • method used for K0S, Λ, Ξ, , and  analysis • standard method and v2 vs. minv method give consistent results BG BG (SIG+BG) SIG (SIG+BG) v2TOT(minv) Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  18. TPC FTPC FTPC Systematic Errors Evaluation • Standard method (Event Plane method): - flow vector - event plane angle A. M. Poskanzer, S. A. Voloshin, Phys. Rev. C58, 1671 (1998) Sensitive to non-flow. • Lee-Yang Zero method: - measure flow using genuine correlations among all particles. - flow determined from first minimum r0 of generating function. • FTPC Reaction Plane: - Similar to Event Plane method - Correlate particles in TPC region with FTPC reaction plane. Suppress non-flow. all particles arbitrary variable Quark Matter 2008, Feb. 4 – 10, Jaipur, India R. S. Bhalerao, N. Borghini, J.-Y.Ollitrault, Nucl. Phy. A 727 (2003) 373-426

  19. Non-flow systematics • 200 GeV Au+Au 10-40%. • h± (yellow bands): decreasing trend. • PID: no clear pT and PID dependence. • v2{LYZ} < v2{EP}: ~10% effect. • 200 GeV Cu+Cu 0-60%. • v2{EP, FTPC} < v2{EP, TPC}. • larger effect at higher pT. • v2 from two methods consistent for  within large errors. Quark Matter 2008, Feb. 4 – 10, Jaipur, India

  20. System Size and Centrality Dependence PHENIX: Phys. Rev. Lett 98, 162301 (2007) STAR Preliminary • A given centrality of a colliding system: clear scaling with nq. • A given system: stronger flow in more central collisions. • Not observe the part scaling claimed by PHENIX, which is independent on colliding system . Quark Matter 2008, Feb. 4 – 10, Jaipur, India

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