Anisotropic flow at RHIC - selected topics Aihong Tang Aihong Tang, CCAST 04 Beijing

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 04 Beijing

Directed flow Do we see wiggle ? Aihong Tang, CCAST 04 Beijing

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) 024909. L.P. Csernai, D. Roehrich PLB 458, 454 (1999) M.Bleicher and H.Stocker, PLB 526,309(2002) Aihong Tang, CCAST 04 Beijing

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 04 Beijing

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) Aihong Tang, CCAST 04 Beijing

Directed flow at RHIC - 62 GeV No Wiggle in Nch v1 ! STAR Preliminary Aihong Tang, CCAST 04 Beijing

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 04 Beijing

Directed flow at RHIC - Limiting fragmentation STAR Preliminary Aihong Tang, CCAST 04 Beijing

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 04 Beijing

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 04 Beijing

In S. Voloshin’s language Aihong Tang, CCAST 04 Beijing

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 04 Beijing

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 04 Beijing

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

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 04 Beijing

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 04 Beijing

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

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. Aihong Tang, CCAST 04 Beijing

High pt v2 : jet quenching v2{RP} v2{4} J. Adams et al. [STAR collaboration], Nucl-ex/0407007 Persistent v2 up to 7 GeV/c in pt. Aihong Tang, CCAST 04 Beijing

Intermediate pt v2 : energy loss model J. Adams et al. [STAR collaboration], nucl-ex/0407007 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 04 Beijing

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 04 Beijing

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 04 Beijing

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 04 Beijing

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