Non-equilibrium photons from the bottom-up thermalization scenario

TL;DR

This paper calculates the photon spectra during the bottom-up thermalization process in heavy-ion collisions, showing that thermalizing glasma photons dominate the excess photon yield at high energies, with analytical solutions incorporating non-equilibrium effects.

Contribution

It provides analytical calculations of photon spectra during all stages of the bottom-up thermalization, including non-equilibrium effects, and compares results with experimental data.

Findings

Thermalizing glasma photons dominate excess photon production.

Analytical solutions incorporate far-from-equilibrium dynamics.

Good agreement with LHC and RHIC photon data.

Abstract

In this work, I calculate the $p_\perp$ resolved spectra for the three stages of the \textit{bottom-up} scenario, which are comparable to the thermal contribution, particularly at higher values of the saturation scale $Q_S^2$. Analytical solutions are obtained by including a parametrization of scaling solutions from far-from-equilibrium classical statistical lattice simulations into a small angle kinetic rate. Furthermore, a theoretically motivated ansatz is used to account for near-collinear enhancement of the low-$p_\perp$ radiation. The system is phenomenologically constrained using the charge hadron multiplicities from LHC and RHIC as in previous parametric estimates and fair agreement with the data available for photons was found. I find that for this realistic set of parameters, the contribution from the thermalizing glasma dominates the excess photons.