Soft Photons from transport and hydrodynamics at FAIR energies

TL;DR

This paper investigates direct photon production in uranium-uranium collisions at FAIR energies using a hybrid transport and hydrodynamic model, highlighting differences in photon flow to distinguish phase transition scenarios.

Contribution

It introduces a hybrid transport-hydrodynamics approach to calculate photon spectra at FAIR energies, comparing hadronic and phase transition scenarios.

Findings

Photon spectra are dominated by Bremsstrahlung in both scenarios.

Photon flow differences may help distinguish phase transition types.

Hydrodynamic phase inclusion affects photon emission patterns.

Abstract

Direct photon spectra from uranium-uranium collisions at FAIR energies (E(lab) = 35 AGeV) are calculated within the hadronic Ultra-relativistic Quantum Molecular Dynamics transport model. In this microscopic model, one can optionally include a macroscopic intermediate hydrodynamic phase. The hot and dense stage of the collision is then modeled by a hydrodynamical calculation. Photon emission from transport-hydro hybrid calculations is examined for purely hadronic matter and matter that has a cross-over phase transition and a critical end point to deconfined and chirally restored matter at high temperatures. We find the photon spectra in both scenarios to be dominated by Bremsstrahlung. Comparing flow of photons in both cases suggests a way to distinguish these two scenarios.