aihong tang the berkeley school 05 1 open questions in the “perfect fluid” aihong tang

Aihong Tang The Berkeley School 05

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Open Questions in the “Perfect Fluid”Open Questions in the “Perfect Fluid”

Aihong Tang


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Outline

• v2/ scaling • “Elliptic flow” in pp and dAu• v1 wiggle• Puzzle at intermediate pt

• Photon flow


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vv22// scaling scaling

Universal curve?


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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?


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““vv22”in pp and dAu”in pp and dAu

Don’t ask again, we have done it. Case closed.


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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.


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How does elliptic flow evolve from pp to dAu, and AuAu collisions ?


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 .


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Directed FlowDirected Flow

What wiggle #$!?


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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.


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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.


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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.


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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?


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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?


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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)


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Puzzles at Itermediate pt

Can we at least get the sign of v4 right?

Hard shell

W.-S.

Hard sphere



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Does direct photon flow?Does direct photon flow?

Show me the light !


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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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Does direct photon flow?

Phenix, nucl-ex/0503003


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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.

aihong tang the berkeley school 05 1 open questions in the “perfect fluid” aihong tang

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