Direct Photons at RHIC

TL;DR

This paper reviews direct-photon measurements at RHIC, highlighting experimental techniques and findings related to photon yields and correlations in proton-proton and gold-gold collisions, with implications for understanding quark-gluon plasma properties.

Contribution

It provides new measurements of direct-photon yields using electromagnetic calorimetry and virtual photon conversion methods at RHIC energies.

Findings

Photon yields measured for pT > 4 GeV/c in p+p and Au+Au collisions.

Photon-hadron azimuthal correlations analyzed to study photon production mechanisms.

Evidence suggests thermal photons from QGP contribute significantly in Au+Au collisions.

Abstract

A brief overview of direct-photon measurements in p+p and Au+Au collisions at sqrt(s_NN) = 200 GeV with the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) is given. Direct-photon yields for pT > 4 GeV/c and photon-hadron azimuthal correlations were determined with the aid of an electromagnetic calorimeter. By detecting e+e- pairs from the internal conversion of virtual photons direct-photon yields were measured between 1 < pT < 4 GeV/c. In Au+Au collisions thermal photons from a quark-gluon plasma (QGP) are expected to contribute significantly to the total direct-photon yield in this range.