Effect of an anisotropic escape mechanism on elliptic flow in relativistic heavy-ion collisions

TL;DR

This paper investigates how anisotropic escape mechanisms contribute to elliptic flow in relativistic heavy-ion collisions, suggesting that surface bias effects significantly influence observed flow and may lead to underestimation of QCD matter viscosity.

Contribution

It introduces a model that isolates anisotropic escape effects without hydrodynamic expansion, highlighting their substantial role in elliptic flow.

Findings

Surface bias effects significantly contribute to elliptic flow.

Neglecting hydrodynamics isolates the escape mechanism's impact.

Viscosity estimates may be underestimated due to these effects.

Abstract

We study the effect of anisotropic escape mechanism on elliptic flow in relativistic heavy-ion collisions. We use Glauber model to generate initial conditions and ignore hydrodynamic expansion in the transverse direction. We employ Beer-Lambert law to allow for the transmittance of produced hadrons in the medium and calculate the anisotropy generated due to the suppression of particles traversing through the medium. In order to separate non-flow contribution due to surface bias effects, we ignore hydrodynamic expansion in the transverse direction and consider purely longitudinal boost-invariant expansion. We calculate the transverse momentum dependence of elliptic flow, generated from anisotropic escape mechanism due to surface bias effects, for various centralities in $\sqrt{s_{NN}}=200$ GeV Au$+$Au collisions at RHIC and $\sqrt{s_{NN}}=2.76$ TeV Pb$+$Pb collisions at LHC. We find that the surface bias effects have a sizable contribution to the total elliptic flow observed in heavy-ion collisions indicating that the viscosity of the QCD matter extracted from hydrodynamic simulations may be underestimated.