1. Anisotropic flow at RHIC - selected topics
Aihong Tang
Aihong Tang, CCAST Beijing

2. Aihong Tang, CCAST 04 Beijing
Outline
Directed flow
The evolution of “elliptic flow”
Azimuthal correlations in dAu
Anisotropy and correlations at large pt
Summary
Aihong Tang, CCAST Beijing

3. Directed flow Do we see wiggle ?
Aihong Tang, CCAST Beijing

4. Directed flow (v1) and phase transition
Anti-flow/3rd flow component, with QGP  v1 flat at middle rapidity.
flow
antiflow
Brachmann, Soff, Dumitru, Stocker, Maruhn, Greiner Bravina, Rischke , PRC 61 (2000) L.P. Csernai, D. Roehrich PLB 458, 454 (1999) M.Bleicher and H.Stocker, PLB 526,309(2002)
Aihong Tang, CCAST Beijing

5. Directed flow (v1) and baryon stopping
Positive space-momentum correlation, no QGP necessary  v1 wiggle.
RQMD v2.4
R.Snellings, H.Sorge, S.Voloshin, F.Wang, N. Xu, PRL (84) 2803(2000)
Aihong Tang, CCAST Beijing

6. Directed flow at RHIC - 200 GeV
Shows no sign of a “wiggle” (although does not exclude the magnitude as predicted)
nucl-ex/ , PRL (2004)
Aihong Tang, CCAST Beijing

7. Directed flow at RHIC - 62 GeV
No Wiggle in Nch v1 !
STAR
Preliminary
Aihong Tang, CCAST Beijing

8. Directed flow at RHIC - 62 GeV
v1{3} and v1{EP1,EP2} give the same result.
STAR Preliminary
v1{EP1,EP2} from M. Oldenburg
Aihong Tang, CCAST Beijing

9. Directed flow at RHIC - Limiting fragmentation
STAR Preliminary
Aihong Tang, CCAST Beijing

10. Aihong Tang, CCAST 04 Beijing
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) ?
Aihong Tang, CCAST Beijing

11. 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.
Scaling !
Multiplicity independent
Aihong Tang, CCAST Beijing

12. In S. Voloshin’s language
Aihong Tang, CCAST Beijing

13. In J.-Y Ollitrault & N. Borghini’s language
The format of generating function used in cumulant analyses is:
It is good for extracting v2, but it does not scale. If we change it to
Then for a system that is superposition of two independent system 1 and 2, and only “nonflow” correlations are present, we have
So if a Nucleus-Nucleus is a simple superposition of N independent pp collisions, then
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)).
In the case of a second order cumulant, this is
Aihong Tang, CCAST Beijing

14. How does “elliptic” flow evolve from pp to dAu, and AuAu collisions ?
AuAu (flow + non-flow)
STAR
Preliminary
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.
dAu (“some flow”)
pp (non-flow)
Aihong Tang, CCAST Beijing

15. Aihong Tang, CCAST 04 Beijing
Azimuthal correlations in dAu collisions How does “Cronin effect” affect azimuthal correlations in dAu collisions ?
Aihong Tang, CCAST Beijing

16. 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
Aihong Tang, CCAST Beijing

17. Azimuthal correlations in dAu collisions : asymmetry
STAR Preliminary
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.
Aihong Tang, CCAST Beijing

18. Aihong Tang, CCAST 04 Beijing
Anisotropy and correlation at large pt Jet quenching ? Recombination and/or fragmentation ?
Aihong Tang, CCAST Beijing

19. High pt azimuthal correlations : jet quenching
J. Adams et al. [STAR collaboration], Nucl-ex/
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.
Aihong Tang, CCAST Beijing

20. High pt v2 : jet quenching
v2{RP}
v2{4}
J. Adams et al. [STAR collaboration], Nucl-ex/
Persistent v2 up to 7 GeV/c in pt.
Aihong Tang, CCAST Beijing

21. Intermediate pt v2 : energy loss model
J. Adams et al. [STAR collaboration], nucl-ex/
200 GeV data
Hard shell
Hard sphere
Woods-Saxon
v2 curve from Woods-Saxon and Hard Sphere are
our calculations based on ideas of X.N.-Wang and Jiayong Jia.
Energy loss alone can not explain large v2 at intermediate pt.
Aihong Tang, CCAST Beijing

22. Intermediate pt v2 : Recombination and fragmentation
(Chiho Nonaka)
R+F fits the trend, but misses the magnitude a little a bit. Uncertainties in the calculation need to be checked !
Aihong Tang, CCAST Beijing

23. Aihong Tang, CCAST 04 Beijing
Intermediate pt v4
STAR Preliminary
Hard shell
W.-S.
Hard sphere
Energy loss model misses both the sign and magnitude of v4. A challenge for theoretical explanations. (R+F?)
Aihong Tang, CCAST Beijing

24. Aihong Tang, CCAST 04 Beijing
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.
Aihong Tang, CCAST Beijing

25. Aihong Tang, CCAST 04 Beijing
THE END
Aihong Tang, CCAST Beijing