Direct photon calculations in heavy-ion collisions at s(NN)**1/2 = 62.4 - 200 AGeV in a (3+1) dimensional hybrid approach

TL;DR

This paper compares direct photon spectra from heavy-ion collisions at various energies using a hybrid model combining transport and hydrodynamics, finding good agreement with experimental data when including a Quark-Gluon-Plasma phase.

Contribution

It introduces a (3+1)D hybrid approach combining microscopic transport and hydrodynamics to calculate direct photon spectra in heavy-ion collisions.

Findings

Hybrid model agrees with PHENIX data for QGP phase

Viscosity and thermalization impact photon yields

Effective description of high-density collision stages

Abstract

Direct photon spectra from central Au+Au- and Cu+Cu-collisions at sqrt(s_NN) = 62.4, 130 and 200 AGeV are calculated within the microscopic transport model UrQMD and a micro+macro hybrid model. In the latter approach, the high-density part of the transport evolution is replaced by an ideal 3+1-dimensional hydrodynamic calculation. We study the impact of viscosity and full local thermalization and compare the calculations to measurements obtained by the PHENIX collaboration. We find a reasonable agreement with the experimental data for calculations involving a Quark-Gluon-Plasma phase.