1. Aihong Tang The Berkeley School 05 1 Open Questions in the “Perfect Fluid” Aihong Tang

2. Aihong Tang The Berkeley School 05 2 Outline v 2 /  scaling “Elliptic flow” in pp and dAu v 1 wiggle Puzzle at intermediate p t Photon flow

3. Aihong Tang The Berkeley School 05 3 v 2 /  scaling v 2 /  scaling Universal curve?

4. Aihong Tang The Berkeley School 05 4 v 2 /eccentricity : universal curve? Phobos, Phys. Rev. Lett(89), 222301 (2002) STAR, Phys. Rev. C(66), 034904 (2002) NA49,Phys. Rev. C(68), 034903 (2003) Why crossing, not approaching? How does a lighter system like CuCu fit in this curve?

5. Aihong Tang The Berkeley School 05 5 “v 2 ”in pp and dAu “v 2 ”in pp and dAu Don’t ask again, we have done it. Case closed.

6. Aihong Tang The Berkeley School 05 6 How does elliptic flow evolve from pp to dAu, and AuAu collisions ? dAu (“some flow”)pp (non-flow)AuAu (flow + non-flow) In VERY peripheral collisions, azimuthal correlation in AuAu could be dominated by non-flow. At high p t in central collisions, azimuthal correlation in AuAu could be dominated by nonflow. STAR, nucl-ex/0409033 PRC accepted.

7. Aihong Tang The Berkeley School 05 7 How does elliptic flow evolve from pp to dAu, and AuAu collisions ? STAR, nucl-ex/0409033 PRC accepted. Correlation in dAu increases as a function of multiplicity, which is a pattern that is opposite to that in AuAu collisions. In high multiplicity events, the Cronin effect is expected to produce more collective motion among soft particles in order to generate a particle with higher p t.

8. Aihong Tang The Berkeley School 05 8 Directed Flow Directed Flow What wiggle #$!?

9. Aihong Tang The Berkeley School 05 9 Wiggle : RQMD RQMD v2.4 R.Snellings, H.Sorge, S.Voloshin, F.Wang, N. Xu, PRL (84) 2803(2000) Positive space-momentum correlation, no QGP necessary  v 1 wiggle.

10. Aihong Tang The Berkeley School 05 10 Wiggle : uRQMD Marcus Bleicher, Horst Stocker PLB 526, (2002) 309-314 The non-interacting strings employed in the UrQMD approach result in a smaller space-momentum correlations and thus in a smaller “anti-flow” around midrapidity.

11. Aihong Tang The Berkeley School 05 11 Wiggle : phase transition flow antiflow Brachmann, Soff, Dumitru, Stocker, Maruhn, Greiner Bravina, Rischke, PRC 61 (2000) 024909. L.P. Csernai, D. Roehrich PLB 458, 454 (1999) M.Bleicher and H.Stocker, PLB 526,309(2002) Anti-flow/3rd flow component, with QGP  v 1 flat at middle rapidity.

12. Aihong Tang The Berkeley School 05 12 Wiggle : to summarize Nucleon wiggle, Both RQMD and UrQMD give NO wiggle for central collisions (b~3fm), and both give a wiggle at peripheral collisions (b~8-11fm). Only the one-fluid hydro model gives a wiggle for central collisions but only IF there is a phase transition of first order. Pion wiggle, Different model give different results.

13. Aihong Tang The Berkeley School 05 13 Chasing the wiggle : where we are?

14. Aihong Tang The Berkeley School 05 14 Chasing the wiggle : where we are? Charged particles (mostly pions) ! STAR Preliminary

15. Aihong Tang The Berkeley School 05 15 Puzzles at intermediate P t Puzzles at intermediate P t Recombination and/or Energy loss, is that all?

16. Aihong Tang The Berkeley School 05 16 Puzzles at Itermediate p t Althogh R+F reproduces the centrality dependence, still it misses the magnitude. What is the uncertainty in models? A.Tang (for the STAR Collaboration) J. Phys. G : Nucl. Part. Phys. 31 s35-39 (2005) C. Nonaka et al., J. Phys. G : Nucl. Part. Phys. 31 s429-435 (2005)

17. Aihong Tang The Berkeley School 05 17 Puzzles at Itermediate p t Can we at least get the sign of v 4 right? Hard shell W.-S. Hard sphere STAR, nucl-ex/0409033 PRC accepted.

18. Aihong Tang The Berkeley School 05 18 Does direct photon flow? Does direct photon flow? Show me the light !

19. Aihong Tang The Berkeley School 05 19 Does direct photon flow? Argument A: phtons are produced isotropically in the momentum space, they do free stream after being produced : v 2 = 0 (widerly accepted, but never confirmed !) Argument B: Strong space-momentum correlation cause photons to be emitted out-of-plane : v 2 < 0

20. Aihong Tang The Berkeley School 05 20 Does direct photon flow? Phenix, nucl-ex/0503003

21. Aihong Tang The Berkeley School 05 21 Summary v 2 /  scaling needs to be tested with different system sizes and collision energies.v 2 /  scaling needs to be tested with different system sizes and collision energies. There are some collectivities in dAu collisions, especially at Au side, however the “flow” is much weaker (a few hundred times less) than that is in AuAu. There are some collectivities in dAu collisions, especially at Au side, however the “flow” is much weaker (a few hundred times less) than that is in AuAu. v 1 wiggle - let’s see how the identified particle analysis says.v 1 wiggle - let’s see how the identified particle analysis says. v 2 at intermediate pt is still too large to be fit in models. The magnitude of v 4 and its sign needs special attention.v 2 at intermediate pt is still too large to be fit in models. The magnitude of v 4 and its sign needs special attention. Photon flow - Be more open mind.Photon flow - Be more open mind.