# Pseudo-Critical Enhancement of Thermal Photons in Relativistic Heavy-Ion Collisions

## TL;DR

This paper investigates thermal photon production in heavy-ion collisions, introducing a pseudo-critical enhancement scenario to better match experimental data and analyzing the effects of different evolution models on photon emission.

## Contribution

It proposes a pseudo-critical enhancement of thermal emission rates and assesses its impact on photon spectra and flow in heavy-ion collisions.

## Key findings

- Pseudo-critical enhancement improves agreement with experimental photon data.
- Hydrodynamic evolution significantly affects photon emission profiles.
- Enhanced rates lead to better understanding of QGP properties.

## Abstract

We compute the spectra and elliptic flow of thermal photons emitted in ultrarelativistic heavy-ion collisions (URHICs) at RHIC and LHC. The thermal emission rates are taken from complete leading-order rates for the QGP and hadronic many-body calculations including baryons and antibaryons, as well as meson-exchange reactions (including Bremsstrahlung). We first update previous thermal fireball calculations by implementing a lattice-QCD based equation of state and extend them to compare to recent LHC data. We then scrutinize the space-time evolution of Au-Au collisions at RHIC by employing an ideal hydrodynamic model constrained by bulk- and multistrange-hadron spectra and elliptic flow, including a non-vanishing initial flow. We systematically compare the evolutions of temperature, radial flow, azimuthal anisotropy and four-volume, and exhibit the temperature profile of thermal photon radiation. Based on these insights, we put forward a scenario with a "pseudo-critical enhancement" of thermal emission rates, and investigate its impact on RHIC and LHC direct photon data.