Thermal Radiation from an Analytic Hydrodynamic Model with Hadronic and QGP Sources in Heavy-Ion Collisions

TL;DR

This paper presents an analytic hydrodynamic model for thermal photon production in heavy-ion collisions, incorporating QGP and hadronic sources, and compares it with experimental data to study initial temperatures.

Contribution

It extends a relativistic hydrodynamic solution to include a quark-hadron transition, providing an analytic model for thermal photon emission in heavy-ion collisions.

Findings

Model shows good agreement with PHENIX photon spectra data.

Enables analysis of initial temperature dependence on collision centrality.

Provides a benchmark for future thermal radiation studies.

Abstract

In high-energy heavy-ion collisions, a nearly perfect fluid is formed, known as the strongly coupled quark-gluon plasma (QGP). After a short thermalization period, the evolution of this medium can be described by the equations of relativistic hydrodynamics. As the system expands and cools, the QGP undergoes a transition into hadronic matter, marking the onset of quark confinement. Direct photons offer insights into an essential stage of evolution, spanning from the onset of thermalization to the suppression of thermal photon production, which occurs within the hadronic phase. This paper builds upon and extends a previously published solution of relativistic hydrodynamics, incorporating an equation of state that falls within the same class as that predicted by lattice QCD. Based on this solution, a completely analytic model is constructed to describe thermal photon production, accounting for the quark-hadron transition. The model is tested against PHENIX measurements of non-prompt direct photon spectra in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. Good agreement is observed between the model predictions and the experimental data, enabling the investigation of the centrality dependence of the initial temperature. These results provide a benchmark for future theoretical and experimental studies of thermal radiation in heavy-ion collisions.