Constraining the viscous freeze-out distribution function with data obtained at the BNL Relativistic Heavy Ion Collider (RHIC)

TL;DR

This paper examines the viscous correction to the particle distribution function during freeze-out in heavy ion collisions, using RHIC data to challenge the standard quadratic ansatz and propose a more accurate momentum dependence.

Contribution

It introduces a data-driven analysis that constrains the form of the viscous correction, suggesting a momentum dependence between linear and quadratic, improving modeling accuracy.

Findings

Standard quadratic ansatz is disfavored by RHIC data.

Data favors a momentum dependence between linear and quadratic.

Results impact the modeling of viscous effects in heavy ion collision simulations.

Abstract

We investigate the form of the viscous correction to the equilibrium distribution function in the context of a Cooper-Frye freeze out prescription for viscous hydrodynamic simulations of relativistic heavy ion collisions. The standard quadratic ansatz used by all groups for the case of shear viscosity is found to be disfavored by experimental data for v4/(v2)^2 at the Relativistic Heavy Ion Collider, and is unlikely to be correct for the hadron resonance gas present at freeze out. Instead, data for v2(pt) along with v4/(v2)^2 favor a momentum dependence between linear and quadratic.