Thermal photons from heavy ion collisions: A spectral function approach

TL;DR

This paper calculates photon emission rates from a hot hadronic gas using a spectral function approach, integrating these with hydrodynamic models to compare with experimental data from SPS and RHIC, and making predictions for LHC.

Contribution

It introduces a second-order chiral reduction method to compute hadronic photon rates, linking theoretical calculations with experimental observables.

Findings

Computed hadronic photon rates using spectral functions.

Compared theoretical yields with SPS and RHIC data.

Provided predictions for photon production at LHC.

Abstract

We analyze the photon rates from a hadronic gas in equilibrium using chiral reduction formulas and a density expansion. The chiral reduction is carried to second order in the pion density which in principal includes all kinetic processes of the type $X\to \pi\gamma$ and $X\to \pi\pi\gamma$. The resulting rates are encoded in the form of vacuum correlation functions which are amenable to experiment. The hadronic rates computed in this work along with the known perturbative QGP rates are integrated over the space-time evolution of a hydrodynamic model tuned to hadronic observables. The resulting yields are compared to the recent photon and low mass dilepton measurements at the SPS and RHIC. Predictions for the LHC are made.