Anisotropy Parameters in Au+Au Collisions at √sNN = 200 GeV at RHIC: Results from the STAR Collaboration

1. PID v2 and v4 from Au+Au Collisions at √sNN = 200 GeV at RHIC N. Li for the STAR Collaboration Lawrence Berkeley National Laboratory, Berkeley Institute of Particle Physics, Wuhan, China

2. Outline • Motivation • Analysis • Results • Summary Na Li 25th Winter Workshop on Nuclear Dynamics

3. Motivation • Formation of QGP in high-energy • nuclear collisions: • De-confinement • Collectivity • Local thermalization • Important questions • We study with dataset of highest statistics Na Li 25th Winter Workshop on Nuclear Dynamics

4. Anisotropy Parameters spatial space anisotropy • Azimuthal correlation with • the reaction plane. • Built up in the early stage, • therefore supplies the • early information of matter • generated in the collision. momentum space anisotropy Na Li 25th Winter Workshop on Nuclear Dynamics

5. Hydro ReCo & Coalescence pQCD Motivation (cont.) • Study the PID dependence of v2 and v4. • Study Number-of-Quark scaling. • Range? • v4/v22 : a probe of ideal hydro behavior. STAR: Phys. Rev. C 77 (2008) 54901 R. S. Bhalerao et.al PLB 627, 49; Borghini and Ollitrault, PLB 642, 227 Na Li 25th Winter Workshop on Nuclear Dynamics

6. Anisotropy Parameter v2 STAR: Phys. Rev. C 77 (2008) 54901 • How about the • higher order • anisotropic flow • such as v4? • Baryon and meson elliptic flow follow the number of • quark ( Nq) scaling. • Indicates that partonic flow builds up at RHIC. Na Li 25th Winter Workshop on Nuclear Dynamics

7. Anisotropy Parameter v2 v4 STAR: Aihong Tang, Proc. 24th Winter Workshop on Nuclear Dynamics Peter Kolb, PRC 68, 031902 • v4 : 4th harmonic • If system reaches local thermal equilibrium, according to ideal hydro dynamic calculation, v4/v22 approaches 0.5 at high pT region. • Directly related to the degree of thermalization of the medium. Hydro, Boltzmann calculations: J. –Y. Ollitrault Na Li 25th Winter Workshop on Nuclear Dynamics

8. Dataset and Cuts • System: Au+Au collision • Energy : sNN = 200 GeV • Event sample : ~60 M events • Year: 2007 • Pseudorapidity range: TPC : -1.0 < η < 1 FTPC : -4.0 < η < -2.5 (east) 2.5 < η < 4.0 (west) Tracks used for TPC event plane: No. of fit hits > 15 No. of fit hits/No. of possible hits >0.52 0.1 < pT < 2.0 GeV/c |η| < 1.0 Tracks used for FTPC event plane: 6 =< No. of fit hits < 12 No. of fit hits/No. of possible hits > 0.52 0.1 < pT < 2.0 GeV/c 2.5< |η| < 4.0 Na Li 25th Winter Workshop on Nuclear Dynamics

9. TPC Event Plane 2nd harmonic event plane (a) STAR preliminary (c) Event plane angle (Rad) (b) • Detector bias is removed by applying • phi weights to the tracks. • Phi weights are generated by • inverting the normalized phi • distributions of detected tracks for a • large event sample. STAR preliminary Na Li 25th Winter Workshop on Nuclear Dynamics

10. FTPC Event Plane J.Barrette et al. Phys. Rev. C56 (1997)3254 • The event plane distribution is • not flat after phi weight • correction due to several • acceptance effect of FTPC. • Add additional shift correction. • Large η gap is used to reduce • the non-flow effect. Phi weight Phi weight + Shift STAR preliminary Event plane angle (Rad) Na Li 25th Winter Workshop on Nuclear Dynamics

11. Invariant Mass Method STAR preliminary STAR preliminary KS0 Assume Borghiniet al. Phys. Rev. C70 (2006)4905 Na Li 25th Winter Workshop on Nuclear Dynamics

12. Pion and Proton Identification TPC: pi/K ~ 0.7 GeV/c pi+K/p ~1.1 GeV/c pi/p ~ > 3GeV/c relativistic rise Cuts used for identification: No. of fit hits > 15 No. of fit hits/No. of possible hits >0.52 pT < 1 (GeV/c) -2 < nσπ (p) < 2 pT > 2.5 (GeV/c)0 < nσπ < 1 -1 < nσp < 0 M. Shao, et al., Nuclear Instruments and Methods in Physics Research A 558 (2006) 419-429 • pion purity: over 95% • proton purity: 70% • The effect on proton v2 will be about 10%. Using Run 4 data result Na Li 25th Winter Workshop on Nuclear Dynamics

13. v2{TPC} and v2{FTPC} Au+Au 200GeV (minibias) STAR preliminary STAR preliminary • v2(pT) have been measured for , p, KS0 and . • Non-flow effect reduced considerably by using the • FTPC event plane. Na Li 25th Winter Workshop on Nuclear Dynamics

14. Number of Quark (Nq) Scaling STAR preliminary STAR preliminary • The number of quark scaling for , KS0 and  holds • up to (mT – m)/nq ~ 1 GeV/c2. • Protons seem to deviate from the scaling at lower pT. Na Li 25th Winter Workshop on Nuclear Dynamics

15. v4{TPC} STAR preliminary STAR preliminary • v4(pT) has been measured for , KS0 and . • The Nq scaling for v4 is observed at (mT - m)/nq < 1 GeV/c2, • similar to that of v2. Na Li 25th Winter Workshop on Nuclear Dynamics

16. Test of Ideal Hydro Predictions STAR preliminary • v4 /v22 is about 1 at pT ~ 2 GeV/c, larger than the value • 0.5 expected from ideal fluid calculations. Na Li 25th Winter Workshop on Nuclear Dynamics

17. Summary • FTPC event plane is used in STAR in order to reduce the • non-flow effect. Run 7 high statistics data used in this • analysis. • Proton and anti-proton seems to deviate from the • number of quark scaling at (mT - m)/nq ~ 1 GeV/c2 . • The number of quark scaling has been observed for v4 at • (mT - m)/nq < 1 GeV/c2. • Mesons and baryons (, KS0 and ) have similar v4/(v2)2 • ratios. It is close to unity at pT > 1 GeV/c, higher than • ideal hydrodynamic model predictions. Na Li 25th Winter Workshop on Nuclear Dynamics

18. BACK UP Na Li 25th Winter Workshop on Nuclear Dynamics

19. Number of Quark (Nq) Scaling STAR preliminary STAR preliminary Na Li 25th Winter Workshop on Nuclear Dynamics