Viscous photons in relativistic heavy ion collisions

TL;DR

This paper investigates how viscous hydrodynamics influences thermal photon production and anisotropy in relativistic heavy ion collisions, emphasizing the sensitivity of photon v2 to microscopic dynamics and initial conditions.

Contribution

It provides a detailed analysis of thermal photon production using viscous hydrodynamics, highlighting the impact of shear viscosity and initial state morphology on photon observables.

Findings

Photon v2 is highly sensitive to shear viscosity (eta/s).

Viscous effects significantly alter the photon spectrum and anisotropy.

Different initial conditions lead to measurable changes in photon observables.

Abstract

Theoretical studies of the production of real thermal photons in relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are performed. The space-time evolution of the colliding system is modelled using MUSIC, a 3+1D relativistic hydrodynamic simulation, using both its ideal and viscous versions. The inclusive spectrum and its azimuthal angular anisotropy are studied separately, and the relative contributions of the different photon sources are highlighted. It is shown that the photon v2 coefficient is especially sensitive to the details of the microscopic dynamics like the equation of state, the ratio of shear viscosity over entropy density, eta/s, and to the morphology of the initial state.