Is there hydrodynamic flow at RHIC ?

TL;DR

This paper argues that azimuthal particle distribution alone cannot confirm hydrodynamic behavior at RHIC, proposing a correlation pattern to distinguish early-stage interactions like re-scattering and string melting.

Contribution

It introduces a spatial-dependent azimuthal multiplicity-correlation pattern to better identify early-stage interactions in heavy-ion collisions at RHIC.

Findings

Re-scattering and string melting interactions are evident in the correlation pattern.

Azimuthal distribution alone is insufficient to confirm hydrodynamic flow.

Early-stage interactions differ from elliptic flow driven by anisotropic expansion.

Abstract

It is argued that the observation of anisotropic azimuthal distribution of final state particles alone is insufficient to show whether the formed matter at RHIC behaves like hydrodynamic flow. Examining the intrinsic interaction (or correlation) of the formed matter should provide more definite judgement. To the end, a spatial-dependent azimuthal multiplicity-correlation pattern is suggested. It shows clearly in the pattern that there are two kinds of interactions at the early stage of Au + Au collisions at $\sqnn=200$ GeV generated by RQMD with hadron re-scattering and AMPT with string melting. This is out of the expectation from the elliptic flow driven by anisotropic expansion.