Exploring Particle Anisotropy in Collisions

1. vn in PHENIX John Chin-Hao ChenRIKEN Brookhaven Research Center INT Ridge Workshop2012/05/08 John C.-H. Chen

2. vn: particle anisotropy • The colliding area is “almond” like shape due to overlap of two colliding nuclei. • The particle angular distribution: dN/d(f-y) =N0(S(1+2vncosn(f-y))) • v2 = elliptic flow John C.-H. Chen

3. Many information coming from flow • Equation of State (EOS) • shear viscosity (η), • specific viscosity (η/s) of sQGP • and their temperature dependence • Key to understand the QGP! John C.-H. Chen

4. Fluctuation matters • Nucleon distribution is not smooth, or initial state fluctuation -> finite vodd • Azimuthal symmetry of the colliding area no longer available • vodd is possible • We can “measure” the fluctuations directly John C.-H. Chen

5. v3, reason for ridge and shoulder? • Ridge sits at Df ~ 0, shoulder sits at Df~2p/3, 4p/3 • A 3-peak structure! • v3 (Fourier Coefficient of thecos3Df term) gives a natural 3-peak structure • Is v3 the explanation? John C.-H. Chen

6. How do we measure vn? • Reaction plane method • Use forward detector to determine the n-th reaction plane, Yn • dN/df 1+S2vncos n(f-Yn) • vn = <cos n(f-Yn)> • Two particle correlation method • central-central or central-forward correlation • dNpair/dDf 1+S(2vnAvnBcosnDf) John C.-H. Chen

7. John C.-H. Chen

8. Reaction plane method • vn {Yn} = <cos(n(f-Fnave))> / Res(Yn) • Fnave is the average of the raw reaction plane between north and south sub-events • Res(Yn) is the reaction plane resolution John C.-H. Chen

9. Correlation factor • Res(Yn), Resolution of reaction plane measures cosine of dispersion of Y estimator (F) from truth • Res(Y2) = <cos(2(Y2(N/S) – YRP))> = sqrt(<cos2(Y2N – Y2S)>) • Key Quantity: cosine of dispersion (Raw vn of YA wrt YB) • <cos j (YmN – YnS)> John C.-H. Chen

10. Reaction plane correlation (i) A: RXN North [1.0-2.8] B: BBC South [3.1-3.9] C: MPC North [3.1-3.7] D: MPC South [3.1-3.7] • <cos j (FmA – FnB)> • N-th reaction plane (Fn) correlates across large rapidity (|hA-hB|~5, |hC-hD|~7) • N = 1 (F1) has negative correlation due to conservation of momentum PRL 107 252301 (2011) John C.-H. Chen

11. Reaction plane correlation (II) A: RXN North [1.0-2.8] B: BBC South [3.1-3.9] C: MPC North [3.1-3.7] D: MPC South [3.1-3.7] • F2 correlates with F1 • F2 correlates with F4 • F2does not correlate with F3 • F1correlates negatively with F3, • some intrinsic v3 not coming from fluctuation? PRL 107 252301 (2011) John C.-H. Chen

12. vn(Yn) vs pT PRL 107 252301 (2011) • All vn increases with pT • v3 is independent from centrality John C.-H. Chen

13. Characterize the initial state anisotropy • Glauber initial state condition • use en to measure the initial state anisotropy John C.-H. Chen

14. vn vs en • vn follows the trend of en • Initial state anisotropy translate to final state momentum anisotropy John C.-H. Chen

15. v3(2p) vs v3(Y3) • v3 measured by two particle correlation method (0.3<|Dh|<0.7) is consistent with, but slightly higher than the reaction plane method • Contributions from non-flow (jet contribution) in this Dh range John C.-H. Chen

16. vn vs theory PRL 107 252301 (2011) • All theory predicts v2 well • v3 adds in additional discrimination power • Data favors Glauber + h/s = 1/4p John C.-H. Chen

17. Jet shape with higher vn modulated background subtraction 200GeV Au+Au 0-20%, inc. g-had. • When v3 modulation is included, the double peak structure in away-side disappears. John C.-H. Chen

18. v2 of Identified particles • v2 of identified particles are measured • (v2/nq) are the same for all particles • Flow exists at partonic level John C.-H. Chen

19. High pT PID v2 arxiv:1203.2644 • new detector TOFw and Aerogel enhance PID capability • Dedicated reaction plane detector • Extend to high pT John C.-H. Chen

20. NQS breaks? arxiv:1203.2644 • NQS holds at 0-20% • Obviously breaks at 20-60% at KET/nq > 1.0 GeV John C.-H. Chen

21. KET/nq scaling vs centrality • With finer centrality bins, the centrality dependence is clear • KET/nq scaling works at 0-10% • It starts breaking at 10-20% at KET/nq~ 1.0 GeV Arxiv:1203.2644 John C.-H. Chen

22. PID v3 @ 200 GeV Au+Au • Mass ordering at low pT • Baryon/meson splitting at intermediate pT John C.-H. Chen

23. NQS of PID v3 • Similar (v3/nq) scaling exists in v3 • v3 also shown in partonic level John C.-H. Chen

24. QCD phase transition • QGP is created at RHIC at 200 GeV • RHIC is flexible in beam energy • Down to 7.7 GeV • Can we find the critical point? • Any significant feature? John C.-H. Chen

25. vn{yn} at 39 GeV • Inclusive charged hadrons • Significant values of v3 and v4 • Trend similar to vn at 200 GeV John C.-H. Chen

26. Beam energy dependence of vn • Various beam energy: 39, 62, 200 GeV • No significant beam energy dependence • Hydro dynamical behavior down to 39 GeV John C.-H. Chen

27. PID v2 @ 62.4 and 39 GeV • NQS scaling still works at 39 GeV! John C.-H. Chen 27

28. v2 measurement in broad energy range • At 7.7 GeV, the v2 value is significantly lower than 200 GeV • A possible transition between 7.7 and 39 GeV? John C.-H. Chen

29. Saturation function of vn • Not only v2 is saturated, but also the v3 and v4, starting from 39 GeV John C.-H. Chen

30. summary • vn has been measured systematically in PHENIX • vn is independent from beam energy between 39 GeV to 200 GeV • KET/nq scaling work on PID v2 from 39-200 GeV • But the KET/nq scaling breaks at large KET/nq in mid-central collisions John C.-H. Chen