Collective Effects in a Medium and a Model of Compound Flow in Relativistic Heavy Ion Collisions

A new analytical approach is presented for analysis of two-particle azimuthal correlations in heavy ion collisions at relativistic energies. This approach suggests that elliptic flow measured by experiment has a compound structure, namely, that it may come from superposition of several components. General expressions have been derived for the two-particle correlation function isolating the contribution due to anisotropic flow. The model of compound flow takes into account the number of jets per event, average multiplicity per jet, dependence of jet yield on the orientation with respect to the reaction plane, and independent ”soft” particle production. These analytic calculations provide the framework for a consistent description of the elliptic flow measured via the single-particle distribution with respect to the reaction plane, jet yield per event, and the amplitude of flow-like modulation in the two-particle distribution in the relative azimuthal angle.