Photons from thermalizing matter in heavy ion collisions

TL;DR

This paper develops an analytic model for direct photon production during the thermalization phase in heavy ion collisions, comparing it with experimental data and providing predictions for future experiments.

Contribution

It introduces a new analytic formula for photon yield from thermalizing matter, relating the bottom-up thermalization scenario to the Glasma framework.

Findings

The model agrees with PHENIX data at 200 GeV.

Predictions for photon yields in various collision systems and energies.

Provides a framework for estimating thermal photon production without prompt contributions.

Abstract

We investigate the production of direct photons in heavy ion collisions within the modified bottom-up thermalization scenario, which we show to be related to the thermalizing Glasma framework. The dynamics of the parton system up to thermalization/equilibration can be described by two momentum scales, by means of which we express the photon invariant yield excluding the prompt pQCD contribution. We derive an analytic formula, which provides an estimate of photon production from thermalizing matter for a wide range of collision systems and energies. We compare the yield with that measured in the PHENIX Au+Au run04 and the combined run07+run10 data sets at root-s = 200GeV. We also make theory-data comparisons for Pb+Pb at 2760 GeV and d+Au at 200 GeV collision energies. Finally, we make predictions for the direct photon invariant yield from collisions of U+U, Cu+Au, $^3$He+Au at 200 GeV and Pb+Pb at 5020 GeV.