Direct photon production in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV at STAR

TL;DR

This paper reports measurements of direct photon production in gold-gold collisions at 200 GeV, revealing an excess over scaled proton-proton references in the 1-4 GeV/c transverse momentum range, consistent with thermal and initial hard scattering models.

Contribution

First measurement of direct photon yield in Au+Au collisions at 200 GeV using dielectron continuum method, showing excess consistent with thermal radiation and hard scattering.

Findings

Observed excess in photon yield in 1-4 GeV/c range.

Results agree with models including thermal radiation and initial hard scattering.

Provides insight into the hot medium created in heavy-ion collisions.

Abstract

We present the direct photon production for $1<p_{T}<10$ GeV/$c$ derived from continuum in the dielectron invariant mass region $0.1<M_{ee}<0.3$ GeV/$c^{2}$ from one billion $\sqrt{s_{NN}}=200$ GeV Au+Au events taken in year 2010 and 2011. A clear excess in the invariant yield compared to the number of binary collision scaled $p+p$ reference is observed in the \pt~range 1-4 GeV/$c$. Model calculations with contributions from thermal radiation and initial hard parton scattering are consistent within uncertainties with the direct photon invariant yield.