Saturation of elliptic flow and shear viscosity

TL;DR

This paper investigates how shear viscosity affects elliptic flow in relativistic heavy-ion collisions, showing that minimal viscosity models better match experimental data up to moderate transverse momentum, but do not reproduce flow saturation at high momentum.

Contribution

It demonstrates that causal dissipative hydrodynamics with minimal shear viscosity can accurately describe elliptic flow data up to higher transverse momentum than ideal hydrodynamics, highlighting the importance of viscosity.

Findings

Viscous hydrodynamics reduces elliptic flow compared to ideal models.

Minimal shear viscosity ($/s=0.08$) explains PHENIX data up to $p_T\u22483.6$ GeV.

Ideal hydrodynamics fits data only up to $p_T$ GeV.

Abstract

Effect of shear viscosity on elliptic flow is studied in causal dissipative hydrodynamics in 2+1 dimensions. Elliptic flow is reduced in viscous dynamics. Causal evolution of minimally viscous fluid ($\eta/s$=0.08), can explain the PHENIX data on elliptic flow in 16-23% Au+Au collisions up to $p_T\approx$3.6 GeV. In contrast, ideal hydrodynamics, can explain the same data only up to $p_T\approx$1.5 GeV. $p_T$ spectra of identified particles are also better explained in minimally viscous fluid than in ideal dynamics. However, saturation of elliptic flow at large $p_T$ is not reproduced.