Initial temperature and EoS of quark matter from direct photons

TL;DR

This paper uses hydrodynamical models to analyze direct photon spectra from RHIC collisions, estimating the initial temperature and equation of state of quark-gluon plasma.

Contribution

It introduces a 3+1D hydrodynamical model to extract initial temperature and EoS parameters from photon data, advancing understanding of quark matter evolution.

Findings

Initial temperature of at least 519 MeV

Equation of state with c_s= 0.36

Consistent with previous hadronic spectra fits

Abstract

The time evolution of the quark gluon plasma created in gold-gold collisions of the Relativistic Heavy Ion Collider (RHIC) can be described by hydrodynamical models. Distribution of hadrons reflects the freeze-out state of the matter. To investigate the time evolution one needs to analyze penetrating probes, such as direct photon spectra. Distributions of low energy photons was published in 2010 by PHENIX. In this paper we analyze a 3+1 dimensional solution of relativistic hydrodynamics and calculate momentum distribution of direct photons. Using earlier fits of this model to hadronic spectra, we compare photon calculations to measurements and find that the initial temperature of the center of the fireball is at least 519+-12 MeV, while for the equation of state we get c_s= 0.36+-0.02.