open questions in the “perfect fluid”
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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?. - PowerPoint PPT PresentationTRANSCRIPT
Aihong Tang The Berkeley School 05
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Open Questions in the “Perfect Fluid”Open Questions in the “Perfect Fluid”
Aihong Tang
Aihong Tang The Berkeley School 05
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Outline
• v2/ scaling • “Elliptic flow” in pp and dAu• v1 wiggle• Puzzle at intermediate pt
• Photon flow
Aihong Tang The Berkeley School 05
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vv22// scaling scaling
Universal curve?
Aihong Tang The Berkeley School 05
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v2/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?
Aihong Tang The Berkeley School 05
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““vv22”in pp and dAu”in pp and dAu
Don’t ask again, we have done it. Case closed.
Aihong Tang The Berkeley School 05
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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 pt in central collisions, azimuthal correlation in AuAu could be dominated by nonflow.
€
ubQ* AA
≈ vbv pMAA + ubQ
* pp
STAR, nucl-ex/0409033 PRC accepted.
Aihong Tang The Berkeley School 05
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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 pt .
Aihong Tang The Berkeley School 05
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Directed FlowDirected Flow
What wiggle #$!?
Aihong Tang The Berkeley School 05
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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 v1 wiggle.
Aihong Tang The Berkeley School 05
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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
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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 v1 flat at middle rapidity.
Aihong Tang The Berkeley School 05
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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.
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Chasing the wiggle : where we are?
Charged particles (mostly pions) !
STAR Preliminary
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Puzzles at intermediate PPuzzles at intermediate Ptt
Recombination and/or Energy loss, is that all?
Aihong Tang The Berkeley School 05
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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
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Puzzles at Itermediate pt
Can we at least get the sign of v4 right?
Hard shell
W.-S.
Hard sphere
STAR, nucl-ex/0409033 PRC accepted.
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Does direct photon flow?Does direct photon flow?
Show me the light !
Aihong Tang The Berkeley School 05
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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
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Summary
• vv22// scaling needs to be tested with different system sizes scaling needs to be tested with different system sizes and collision energies.and collision energies.
• There are some collectivities in dAu collisions, especially at There are some collectivities in dAu collisions, especially at Au side, however the “flow” is much weaker (a few hundred Au side, however the “flow” is much weaker (a few hundred times less) than that is in AuAu.times less) than that is in AuAu.
• vv11 wiggle - let’s see how the identified particle analysis says. wiggle - let’s see how the identified particle analysis says.
• vv22 at intermediate pt is still too large to be fit in models. The at intermediate pt is still too large to be fit in models. The magnitude of magnitude of vv44 and its sign needs special attention. and its sign needs special attention.
• Photon flow - Be more open mind. Photon flow - Be more open mind.