v4 for identified particles at RHIC from viscous hydrodynamics

TL;DR

This paper investigates the ratio of azimuthal flow harmonics v4 to v2 squared for identified particles in RHIC collisions using viscous hydrodynamics, revealing how viscosity and freeze-out corrections affect this ratio.

Contribution

It introduces a modified viscous correction to the distribution function that restores the flatness of v4/(v2)^2 as a function of transverse momentum.

Findings

Viscous effects depend little on particle species.

Standard viscous correction destroys the flatness of the ratio.

Modified correction restores the flatness of v4/(v2)^2.

Abstract

Using ideal and viscous hydrodynamics, the ratio of azimuthal moments v4/(v2)^2 is calculated for pions, protons, and kaons in sqrt{s}=200 A*GeV Au+Au collisions. For any value of viscosity here is little dependence on particle species. Ideal hydrodynamics and data show a flat curve as a function of pt. Adding viscosity in the standard way destroys this flatness. However, it can be restored by replacing the standard quadratic ansatz for delta f (the viscous correction to the distribution function at freeze-out) with a weaker momentum dependence.