On elliptic flow and the blast-wave model

TL;DR

This paper reviews extensions of the blast-wave model for non-central heavy-ion collisions, explaining how anisotropies influence elliptic flow and discussing model limitations and comparisons with experimental data.

Contribution

It provides a comprehensive review of blast-wave model extensions, clarifies the physics of anisotropic flow, and compares models with data to assess their validity.

Findings

Second-order anisotropy affects elliptic flow

Model comparisons highlight limitations in reproducing all data

Multiple particle species comparisons are essential for meaningful analysis

Abstract

Extensions of the blast-wave model for the description of non-central collisions are reviewed and the physics behind them is explained and illustrated. It is shown how the second-order anisotropy in expansion velocity together with the anisotropy in the shape or the density profile of the fireball determine the elliptic flow of the produced hadrons. Ambiguities and limitations of the models are discussed and different models are compared among themselves and with example data. It is concluded that model results should always be compared to $v_2(p_t)$ from several identified species in order to receive meaningful results about the freeze-out stage of the fireball and that even such a comparison may not be conclusive as the models may not be able to reproduce all relevant data.