Anisotropic Flow at the SPS and RHIC

The results on directed and elliptic flow for Pb + Pb at the full energy of the SPS (158 GeV/A) and from the first year of Au + Au at RHIC (sqrt{s_{_{NN}}=130 GeV) are reviewed. The different experiments agree well and a consistent picture has emerged indicating early time thermalization at RHIC.Comment: 4 pages. For the proceedings of the International Workshop on the Physics of the Quark-Gluon Plasma, Palaiseau, France, 4-7 Sept. 0

Directed and Elliptic Flow in Pb+Pb collisions at 40 and 158 AGeV

Directed and elliptic flow are reported for charged pions and protons as a function of transverse momentum, rapidity, and centrality in 40 and 158 AGeV Pb + Pb collisions. The standard method of correlating particles with an event plane is used. The directed flow of protons is small and shows little variation near to midrapidity, but rises fast towards projectile rapidity in the 40 AGeV data. For most peripheral collisions the flat region becomes negative resulting in $v_1$ changing sign three times. Elliptic flow doesn't seem to change very much from 40 AGeV to 158 AGeV. The difference is smaller than anticipated from the overall energy dependence from AGS to RHIC.Comment: Presented at 16th International Conference on Ultrarelativistic Nucleus-Nucelus Collisions, Quark Matter 2002 (QM 2002), Nantes, France, 18-24 Jul 2002, 4 pages, 3 figure

Forward-rapidity azimuthal and radial flow of identified particles for sNN\sqrt{s_{NN}} = 200 GeV Au+Au collisions

A strong azimuthal flow signature at RHIC suggests rapid system equilibration leading to an almost perfect fluid state. The longitudinal extent of the flow behavior depends on how this state is formed and can be studied by measuring the pseudorapidity and transverse momentum dependence of the second Fourier component ($v_{2}(p_{T})$) of the azimuthal angular distribution. We report on a measurement of identified-particle $v_{2}$ as a function of $p_{T}$ (0.5-2.0 GeV/c), centrality (0-25%, 25-50%), and pseudorapidity ($0\leq\eta<3.2$) for $\sqrt{s_{NN}} = 200 \rm GeV$ Au+Au collisions. The BRAHMS spectrometers are used for particle identification ($\pi$, K, p) and momentum determination and the BRAHMS global detectors are used to determine the corresponding reaction-plane angles. The results are discussed in terms of the rapidity dependence of constituent quark scaling and in terms of models that develop the complete (azimuthal and radial) hydrodynamic aspects of the forward dynamics at RHIC.Comment: 4 pages, 4 figures - To appear in the conference proceedings for Quark Matter 2009, March 30-April 4, Knoxville, Tennesse

Effect of flow fluctuations and nonflow on elliptic flow methods

We discuss how the different estimates of elliptic flow are influenced by flow fluctuations and nonflow effects. It is explained why the event-plane method yields estimates between the two-particle correlation methods and the multiparticle correlation methods. It is argued that nonflow effects and fluctuations cannot be disentangled without other assumptions. However, we provide equations where, with reasonable assumptions about fluctuations and nonflow, all measured values of elliptic flow converge to a unique mean v_{2,PP} elliptic flow in the participant plane and, with a Gaussian assumption on eccentricity fluctuations, can be converted to the mean v_{2,RP} in the reaction plane. Thus, the 20% spread in observed elliptic flow measurements from different analysis methods is no longer mysterious.Comment: one typo in Table I correcte

Collective phenomena in non-central nuclear collisions

Recent developments in the field of anisotropic flow in nuclear collision are reviewed. The results from the top AGS energy to the top RHIC energy are discussed with emphasis on techniques, interpretation, and uncertainties in the measurements.Comment: Review paper, 56 pages, as accepted for publicatio

Centrality dependence of directed and elliptic flow at the SPS

New data with a minimum bias trigger for 158 GeV/nucleon Pb + Pb have been analyzed. Directed and elliptic flow as a function of rapidity of the particles and centrality of the collision are presented. The centrality dependence of the ratio of elliptic flow to the initial space elliptic anisotropy is compared to models

Measurement of Event Plane Correlations in Pb-Pb Collisions at sNN\sqrt{s_{\mathrm{NN}}}=2.76 TeV with the ATLAS Detector

A measurement of correlations between event-plane angles $\Phi_n$ is presented as a function of centrality for Pb-Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=2.76$ TeV. These correlations are estimated from observed event-plane angles $\Psi_n$ obtained from charged particle or transverse energy flow measured over a large pseudorapidity range $|\eta|<4.8$, followed by a resolution correction that accounts for the dispersion of $\Psi_n$ relative to $\Phi_n$. Various correlators involving two or three event planes with acceptable resolution are measured. Significant positive correlations are observed for $4(\Phi_2-\Phi_4)$, $6(\Phi_2-\Phi_6)$, $6(\Phi_3-\Phi_6)$, $2\Phi_2+3\Phi_3-5\Phi_5$, $2\Phi_2+4\Phi_4-6\Phi_6$ and $-10\Phi_2+4\Phi_4+6\Phi_6$. However, the measured correlations for $2\Phi_2-6\Phi_3+4\Phi_4$ are negative. These results may shed light on the patterns of the fluctuation of the created matter in the initial state as well as the subsequent hydrodynamic evolution.Comment: 5 pages, 4 figures. Proceedings for Hard Probes 2012, Cagliari, Ital