A Systematic Study on Direct Photon Production from Central Heavy Ion Collisions

TL;DR

This paper systematically analyzes direct photon production in central heavy-ion collisions at RHIC, considering thermal, hard, and bremsstrahlung sources, and evaluates their relative contributions and effects of energy loss.

Contribution

It provides a comprehensive study including all photon sources in heavy-ion collisions with realistic thermodynamic modeling and energy loss effects.

Findings

Thermal photons from quark-gluon plasma and hadron gas are significant.

Primordial elementary scatterings dominate at high transverse momentum.

Secondary photons from jet processes and energy loss are non-negligible.

Abstract

We investigate the production of direct photons in central Au-Au collisions at the relativistic Heavy-Ion Collider (RHIC) at 200 GeV per nucleon, considering all possible sources. We treat thermal photons emitted from a quark-gluon plasma and from a hadron gas, based on a realistic thermodynamic expansion. Hard photons from elementary nucleon-nucleon scatterings are included: primordial elementary scatterings are certainly dominant at large transverse momenta, but also secondary photons from jet fragmentation and jet-photon conversion cannot be ignored. In both cases we study the effect of energy loss, and we also consider photons emitted from bremsstrahlung gluons via fragmentation.