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Open Questions in the “Perfect Fluid”

Open Questions in the “Perfect Fluid”. Aihong Tang. Outline. v 2 /  scaling “Elliptic flow” in pp and dAu v 1 wiggle Puzzle at intermediate p t Photon flow. v 2 /  scaling Universal curve?. v 2 /eccentricity : universal curve?. Why crossing, not approaching?.

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Open Questions in the “Perfect Fluid”

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

  2. Outline • v2/ scaling • “Elliptic flow” in pp and dAu • v1 wiggle • Puzzle at intermediate pt • Photon flow Aihong Tang The Berkeley School 05

  3. v2/ scalingUniversal curve? Aihong Tang The Berkeley School 05

  4. v2/eccentricity : universal curve? Why crossing, not approaching? Phobos, Phys. Rev. Lett(89), 222301 (2002) How does a lighter system like CuCu fit in this curve? STAR, Phys. Rev. C(66), 034904 (2002) NA49,Phys. Rev. C(68), 034903 (2003) Aihong Tang The Berkeley School 05

  5. “v2”in pp and dAuDon’t ask again, we have done it. Case closed. Aihong Tang The Berkeley School 05

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

  7. How does elliptic flow evolve from pp to dAu, and 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 pt . Correlation in dAu increases as a function of multiplicity, which is a pattern that is opposite to that in AuAu collisions. STAR, nucl-ex/0409033 PRC accepted. Aihong Tang The Berkeley School 05

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

  9. Wiggle : RQMD RQMD v2.4 Positive space-momentum correlation, no QGP necessary  v1 wiggle. R.Snellings, H.Sorge, S.Voloshin, F.Wang, N. Xu, PRL (84) 2803(2000) 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. Aihong Tang The Berkeley School 05

  11. Wiggle : phase transition flow antiflow Anti-flow/3rd flow component, with QGP  v1 flat at middle rapidity. 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) 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. Aihong Tang The Berkeley School 05

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

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

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

  16. Puzzles at Itermediate pt 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) Aihong Tang The Berkeley School 05

  17. Puzzles at Itermediate pt Hard shell W.-S. Hard sphere STAR, nucl-ex/0409033 PRC accepted. Can we at least get the sign of v4 right? Aihong Tang The Berkeley School 05

  18. Does direct photon flow?Show me the light ! 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 : v2 = 0 (widerly accepted, but never confirmed !) Argument B: Strong space-momentum correlation cause photons to be emitted out-of-plane : v2 < 0 Aihong Tang The Berkeley School 05

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

  21. Summary • v2/ 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. • v1 wiggle - let’s see how the identified particle analysis says. • v2 at intermediate pt is still too large to be fit in models. The magnitude of v4 and its sign needs special attention. • Photon flow - Be more open mind. Aihong Tang The Berkeley School 05

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