The production of photons in relativistic heavy-ion collisions

TL;DR

This paper demonstrates that an advanced hydrodynamical model with updated photon emission rates aligns well with experimental data, indicating thermal photons as the main source of photon anisotropy in heavy-ion collisions.

Contribution

It introduces a comprehensive event-by-event hydrodynamical model incorporating recent developments, viscosities, and their effects on photon emission in heavy-ion collisions.

Findings

Improved agreement with ALICE and PHENIX measurements.

Viscosities significantly affect photon momentum anisotropy.

Thermal photons are confirmed as dominant in direct photon production.

Abstract

In this work it is shown that the use of a hydrodynamical model of heavy ion collisions which incorporates recent developments, together with updated photon emission rates greatly improves agreement with both ALICE and PHENIX measurements of direct photons, supporting the idea that thermal photons are the dominant source of direct photon momentum anisotropy. The event-by-event hydrodynamical model uses IP-Glasma initial states and includes, for the first time, both shear and bulk viscosities, along with second order couplings between the two viscosities. The effect of both shear and bulk viscosities on the photon rates is studied, and those transport coefficients are shown to have measurable consequences on the photon momentum anisotropy.