1. Mass, Quark-number, Energy Dependence of v 2 and v 4 in Relativistic Nucleus- Nucleus Collisions Yan Lu University of Science and Technology of China Many thanks to the organizers.

2. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 2 publication  Phys. Rev. C 75, 054906 (2007)  One of principle authors for STAR collaboration  Most of work done as Ph.D student in CCNU.

3. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 3 Outline  Introduction and Motivation  Experiments  Results and Discussions  Summary

4. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 4 Goal of Heavy Ion Collision QGP is taken to be a (locally) thermalized state of matter in which quarks and gluons are deconfined, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic volumes. RHIC white papers - 2005, Nucl. Phys. A757, STAR: p102; PHENIX: p184. Time Initial conditions Initial hard interactions Hot and dense matter Hadronization and chemical freeze-out Kinetic freeze-out

5. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 5 QGP signature: collective flow In high-energy nuclear collisions, interaction among constituents and density distribution will lead to: pressure gradient  collective flow  Pressure gradient only depends on the density gradient and interactions Experiments: Fourier expansion of the azimuthal p T distribution Reaction plane azimuthal angel Important flow parameters: x z Non-central Collisions Reaction plane: x-z plane

6. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 6 y x pypy pxpx coordinate-space-anisotropy  momentum-space-anisotropy Elliptic flow v 2  Azimuthal anisotropy of density gradient.  Interactions  anisotropy in momentum space.  Self-quench: elliptic flow is sensitive to the early stage.

7. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 7 Results at RHIC Phys. Rev. Lett. 91, 092301, 2003; Nucl. Phys. A 757, 102, 2005, p38  At low p T, the heavier hadron, the smaller v 2 – mass ordering.  At intermediate p T, v 2 depends on number of constituent quark – n q -scaling. Partonic collectivity and de-confinement at RHIC.

8. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 8 Motivation - Gain information on interplay of collectivity, NQ scaling as a function of collision centrality and energy. - Determine parameters for partonic EoS. CollectivityEnergy dependence  n q -scaling

9. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 9 STAR detector  Acceptance: full azimuthal coverage; pseudo-rapidity coverage |  | < 1  Advantage for event-wise correlations.

10. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 10 Particle Identification I  TPC dE/dx PID: pion/kaon: p T ~ 0.6 GeV/c; proton p T ~ 1.2 GeV/c  TOF PID: pion/kaon: p T ~ 1.8 GeV/c; proton p T ~ 3 GeV/c

11. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 11 Particle Identification II  PID extends to high p T.

12. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 12 Event Plane Method  Estimation of the true reaction plane using elliptic flow itself. - flow vector where sum over all particles. - event plane angle  v 2 calculation A. M. Poskanzer, S. A. Voloshin, Phys. Rev. C58, 1671 (1998) Flat distribution.

13. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 13 62.4 GeV Au+Au results  0-80% minimum bias.  Omega, lack of hadronic interaction consistent with mass-ordering.  Achievement of partonic collectivity in 62.4 GeV Au+Au.

14. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 14 Number-of-Quark Scaling  Number-of-Quark Scaling is observed in 62.4 GeV Au+Au.  Better scaling in transverse kinetic energy scale. Kinetic energy: m T – m 0 =  (p T ) 2 + m 0 2 - m 0

15. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 15 Centrality Dependence  v 2 is larger in more peripheral collisions due to larger .  mass-ordering is observed for all centrality intervals.

16. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 16 More Central, stronger flow  Divide  to remove initial geometry effect.  At a given centrality, v 2 follows Number-of-Quark Scaling.  v 2 /  is larger in more central collisions, indicating stronger flow in more central collisions.

17. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 17 v4v4  v 4 scale with 1.2 (v 2 ) 2 ~ (n q ) 2 for meson and baryon.  v 4 tested the constituent quark degree freedom to higher order.

18. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 18 Energy Dependence  Similar v 2 for 62.4 and 200 GeV.  10-15% smaller at SPS than at RHIC.  Onset of limiting behavior toward RHIC energy.

19. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 19 Summary  We report azimuthal anisotropy parameter v 2 of , , p, , ,  from Au+Au collisions at 62.4 GeV. 0%-10%, 10%-40% and 40%-80% centrality bins are presented.  At low p T, mass-ordering is observed.  At intermediate p T, Number-of-Constituent-Quark scaling is observed.  Stronger flow is observed in more central collisions.  Magnitude of v 2 is similar for 62.4 GeV and 200 GeV, 10-15% higher than 17.3 GeV at SPS.

20. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 20 Thanks!

21. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 21 QCD phase diagram Baryon Density

22. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 22 Analysis Method: v 2 vs. m inv V0 reconstruction 68.95% 63.9% v 2 vs. m inv Method assume Robustness: Away-peak points constrain Near-peak points constrain Borghini et al. Phys. Rev. C70 (2004) 064905

23. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 23 y x pypy pxpx coordinate-space-anisotropy  momentum-space-anisotropy Anisotropy Parameter v 2 Initial/final conditions, EoS, degrees of freedom

24. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 24 Goal of Heavy Ion Collision QGP is taken to be a (locally) thermalized state of matter in which quarks and gluons are deconfined, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic volumes. RHIC white papers - 2005, Nucl. Phys. A757, STAR: p102; PHENIX: p184. Time Initial conditions Initial hard interactions Partonic matter — QGP Hadronization and chemical freeze-out Kinetic freeze-out

25. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 25 Relativistic Heavy Ion Collider RHIC BRAHMS PHOBOS PHENIX STAR AGS TANDEMS v = 0.99995  c = 186,000 miles/sec Au + Au at 200 GeV Brookhaven National Laboratory (BNL), Upton, NY

26. 吕 第 10 届粒子物理大会, 南京, April 26-29, 2008 26 Collision Geometry x z Non-central Collisions Au + Au  s NN = 200 GeV Uncorrected Charge particle multiplicity  collision centrality Reaction plane: x-z plane