Direct photon production from hadronic sources in high-energy heavy-ion collisions

TL;DR

This study investigates low transverse momentum direct photon production from hadronic sources in high-energy heavy-ion collisions using a microscopic transport model, highlighting the dominance of bremsstrahlung processes and minimal in-medium effects.

Contribution

It incorporates various hadronic sources and in-medium effects into the HSD transport approach to analyze direct photon emission in heavy-ion collisions.

Findings

Bremsstrahlung processes dominate photon production.

In-medium effects have minimal impact on spectra.

Uncertainties in background subtraction are significant.

Abstract

The low $p_T$ direct photon production from a variety of the hadronic sources is studied within the microscopic HSD transport approach for p+C, p+Pb and Pb+Pb collisions at 160 A GeV. The direct photon emission from elementary hadronic scatterings as well as meson-meson bremsstrahlung are incorporated. The influence of in-medium effects such as a collisional broadening of the vector-meson spectral functions on the photon emission rate is found to be hardly observable in the final spectra which are dominated by bremsstrahlung type processes. The uncertainties in the subtraction of the 'background' from the photon decay of hadronic resonances inside the hot and dense fireball is investigated, additionally. Our findings are relevant for the interpretation and extraction of experimental data on direct photon production at low $p_T$.