Parameterizing Smooth Viscous Fluid Dynamics With a Viscous Blast Wave

TL;DR

This paper evaluates how well viscous blast wave models can replicate fluid dynamic simulations of high-energy nuclear collisions, focusing on temperature and shear viscosity, and provides methods to improve fit accuracy.

Contribution

It systematically compares viscous blast wave fits to fluid dynamic simulations and develops correction maps to enhance parameter extraction accuracy.

Findings

Blast wave fits accurately reproduce shear viscosity.

Temperatures are often underpredicted, especially in peripheral collisions.

Maps from true to fitted parameters help improve fit results.

Abstract

Blast wave fits are widely used in high energy nuclear collisions to capture essential features of global properties of systems near kinetic equilibrium. They usually provide temperature fields and collective velocity fields on a given hypersurface. We systematically compare blast wave fits of fluid dynamic simulations for Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV and Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV with the original simulations. In particular, we investigate how faithful the viscous blast wave introduced in \cite{Yang:2022yxa} can reproduce the given temperature and specific shear viscosity fixed at freeze-out of a viscous fluid dynamic calculation, if the final spectrum and elliptic flow of several particle species are fitted. We find that viscous blast wave fits describe fluid dynamic pseudodata rather well and reproduce the specific shear viscosities to good accuracy. However, extracted temperatures tend to be underpredicted, especially for peripheral collisions. We investigate possible reasons for these deviations. We establish maps from true to fitted values. These maps can be used to improve raw fit results from viscous blast wave fits. Although our work is limited to two specific, albeit important, parameters and two collision systems, the same procedure can be easily generalized to other parameters and collision systems.