Anisotropic flow from Lee-Yang zeroes: a practical guide

We present a new method to analyze anisotropic flow from the genuine correlation among a large number of particles, focusing on the practical implementation of the method.Comment: 4 pages; contribution to Quark Matter 2004, Oakland, January 11-17, 200

Event-plane correlators

Correlators between event planes of different harmonics in relativistic heavy-ion collisions have the potential to provide crucial information on the initial state of the matter formed in these collisions. We present a new procedure for analyzing such correlators, which is less demanding in terms of detector acceptance than the one used recently by the ATLAS collaboration to measure various two-plane and three-plane correlators in Pb-Pb collisions at LHC. It can also be used unambiguously for quantitative comparison between theory and data. We use this procedure to carry out realistic simulations within the transport model AMPT. Our theoretical results are in excellent agreement with the ATLAS data, in contrast with previous hydrodynamic calculations which only achieved qualitative agreement. We present predictions for new correlators, in particular four-plane correlators, which can easily be analyzed with our new method.Comment: 6 pages, 3 figures. v2: Further explanations added; results unchange

Determining initial-state fluctuations from flow measurements in heavy-ion collisions

We present a number of independent flow observables that can be measured using multiparticle azimuthal correlations in heavy-ion collisions. Some of these observables are already well known, such as v2{2} and v2{4}, but most are new--in particular, joint correlations between v1, v2 and v3. Taken together, these measurements will allow for a more precise determination of the medium properties than is currently possible. In particular, by taking ratios of these observables, we construct quantities which are less sensitive to the hydrodynamic response of the medium, and thus more directly characterize the initial-state fluctuations of the event shape, which may constrain models for early-time, non-equilibrium QCD dynamics. We present predictions for these ratios using two Monte-Carlo models, and compare to available data.Comment: 4 pages, 1 figure, figure data included with source; v3: Mistake in the Glauber calculation (Fig. 1) corrected after publication. Noticeable differences in panels 3, 6 and 7 of Fig.1. Conclusions unchange

Eccentricity fluctuations and elliptic flow at RHIC

Fluctuations in nucleon positions can affect the spatial eccentricity of the overlap zone in nucleus-nucleus collisions. We show that elliptic flow should be scaled by different eccentricities depending on which method is used for the flow analysis. These eccentricities are estimated semi-analytically. When $v_2$ is analyzed from 4-particle cumulants, or using the event plane from directed flow in a zero-degree calorimeter, the result is shown to be insensitive to eccentricity fluctuations.Comment: 5 pages, 3 eps figure

Determination of the reaction plane in ultrarelativistic nuclear collisions

In the particles produced in a nuclear collision undergo collective flow, the reaction plane can in principle be determined through a global event analysis. We show here that collective flow can be identified by evaluating the reaction plane independently in two separate rapidity intervals, and studying the correlation between the two results. We give an analytical expression for the correlation function between the two planes as a function of their relative angle. We also discuss how this correlation function is related to the anisotropy of the transverse momentum distribution. Email contact: [email protected]: Saclay-T93/026 Email: [email protected]

Characterization and analysis of azimuthally sensitive correlations

A unified framework for describing the azimuthal dependence of two-particle correlations in heavy-ion collisions is introduced, together with the methods for measuring the corresponding observables. The generalization to azimuthal correlations between more than two particles is presented.Comment: 7 pages; talk given at Hot Quarks 2004, Taos (NM), July 18-24,200