anisotropic flow at rhic - selected topics

Aihong Tang, CCAST 04 Beijing

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QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Anisotropic flow at RHIC - selected topics

Aihong Tang


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are needed to see this picture. Outline

Directed flow

The evolution of “elliptic flow”

Azimuthal correlations in dAu

Anisotropy and correlations at large pt

Summary


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Directed flow

Do we see wiggle ?


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Directed flow (v1) and 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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Directed flow (v1) and baryon stopping

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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are needed to see this picture. Directed flow at RHIC - 200 GeV

Shows no sign of a “wiggle” (although does not exclude the magnitude as predicted)

nucl-ex/0310029, PRL 92 062301(2004)


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No Wiggle in Nch v1 !



STAR Preliminary


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v1{3} and v1{EP1,EP2} give the same result.

STAR Preliminary

v1{EP1,EP2} from M. Oldenburg


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are needed to see this picture. Directed flow at RHIC - Limiting fragmentation

STAR Preliminary


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The evolution of “elliptic flow”

How does “elliptic flow” evolve from elementary collisions (p+p) through collisions involving

cold nuclear matter (d+Au), and then on to hot, dense heavy ion collisions (Au+Au) ?


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are needed to see this picture. We need a fair comparison of “v2” on three different systems

•V2 does not scale --- need to find a multiplicity (or Nbinary) independent

quantity to compare azimuthal correlations between two different systems.

€

M 2 e in(φ1 −φ2 ) = M • M e in(φ1 −φ2 ) = M • uQ* = Mδ2

~

Multiplicity independent

Scaling !


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are needed to see this picture. In S. Voloshin’s language

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ubQ* = vbv p + δbp

AA( )M

AA

€

δbpAA ≈

δbppp

Ncoll≈δbpppM pp

M AA

€

Q = uii∈"pool"

∑ ; ui = e i2φi

v p - Flow in a particle pt/eta "bin"

vb - Average flow for particles used

("pool partiles") to define RP

δbppp - Azimuthal correlations in pp

( uaub* , u = e i2φ )

€

Then non - flow/flow contribution ratio in AA

would be :

δbppp

Ncoll: v2

2

Could be significant for peripheral

(Ncoll ~ 5,v ~ 0.08) or very central

(Ncoll ~ 200,v ~ 0.01) collisions

€

ubQ* AA

≈ vbv pMAA + ubQ

* pp


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are needed to see this picture. In J.-Y Ollitrault & N. Borghini’s language

Log(G(z)) then should scale linearly with the number of pp collisions, so should cumulants, which is the coefficient of z of Log(G(z)).

It is good for extracting v2, but it does not scale. If we change it to

)1()(1

*

∏=

−++=

M

j

inin

n Mzeez

zGjj φφ

The format of generating function used in cumulant analyses is:

)1()(1

*∏=

−++=M

j

ininn

jj zeezzG φφ

Then for a system that is superposition of two independent system 1 and 2, and only “nonflow” correlations are present, we have

)(2)(1)( zGzGzG =So if a Nucleus-Nucleus is a simple superposition of N independent pp collisions, then

€

G(z) = Gpp (z)[ ]N

In the case of a second order cumulant, this is

€

M 2 e in(φ1 −φ2 ) = M • M e in(φ1 −φ2 ) = M • uQ* = Mδ2

~


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are needed to see this picture. How does “elliptic” flow evolve from pp to dAu, and AuAu collisions ?

STAR Preliminary

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


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Azimuthal correlations in dAu collisions

How does “Cronin effect” affect azimuthal correlations in dAu collisions ?


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are needed to see this picture.Azimuthal correlations in dAu collisions : centrality dependence

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 .

STAR Preliminary


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are needed to see this picture.Azimuthal correlations in dAu collisions : asymmetry

More collective motion at pt above 2 GeV/c in the deuteron side and pt < 1 GeV/c in the Au side.

Hard (relative) particles in deutron side correlate with soft particle in Au side - as expected from Cronin effect.

€

Au −1.<η < −0.5( )d 0.5 <η <1( )

STAR Preliminary


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Anisotropy and correlation at large pt

Jet quenching ? Recombination and/or fragmentation ?


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High pt azimuthal correlations : jet quenching

J. Adams et al. [STAR collaboration], Nucl-ex/0407007

Stronger suppression is found in the back-to-back high-pt particle correlations for particles emitted out-of-plane compared to those emitted in-plane.


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High pt v2 : jet quenching

J. Adams et al. [STAR collaboration], Nucl-ex/0407007

v2{2}

v2{RP}

v2{4}

Persistent v2 up to 7 GeV/c in pt.


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v2 curve from Woods-Saxon and Hard Sphere areour calculations based on ideas of X.N.-Wang and Jiayong Jia.

200 GeV data

Hard shellHard shell

Hard sphereHard sphere

Woods-SaxonWoods-Saxon

Intermediate pt v2 : energy loss model

J. Adams et al. [STAR collaboration], nucl-ex/0407007

Energy loss alone can not explain large v2 at intermediate pt.


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Intermediate pt v2 : Recombination and fragmentation

R+F fits the trend, but misses the magnitude a little a bit. Uncertainties in the calculation need to be checked !

(Chiho Nonaka)


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Intermediate pt v4

Hard shell

W.-S.

Hard sphere

Energy loss model misses both the sign and magnitude of v4. A challenge for theoretical explanations. (R+F?)

STAR Preliminary


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are needed to see this picture. Summary

No wiggle is found in Nch v1 at 62 GeV.

Viewed in the projectile frame, v1 at RHIC agrees with NA49 result.

The evolution of “elliptic flow” is discussed. Nonflow is found dominated in peripheral AuAu events and at high pt in central events.

The azimuthal correlation in dAu is consistent with what is expected from Cronin effect.

Anisotropy and correlations at large pt are consistent with “jet quenching”. However the large v2 and v4 from intermediate pt still needs theoretical explanations.


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anisotropic flow at rhic - selected topics

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