High-pT Direct-Photon Results from PHENIX

TL;DR

This paper reports on high-transverse-momentum direct-photon measurements from the PHENIX experiment, showing consistency with QCD predictions in p+p collisions and no suppression in Au+Au collisions, supporting energy loss models.

Contribution

First measurements of high-pT direct photons in p+p and Au+Au collisions at RHIC, confirming scaling and supporting energy loss explanations for hadron suppression.

Findings

p+p results agree with NLO pQCD calculations

Direct-photon yields scale with number of nucleon-nucleon collisions

No strong suppression observed for direct photons in Au+Au collisions

Abstract

Direct-photon measurements in p+p and Au+Au collisions at sqrt{s_{NN}} = 200 GeV from the PHENIX experiment are presented. The p+p results are found to be in good agreement with next-to-leading-order (NLO) perturbative QCD calculations. Direct-photon yields in Au+Au collisions scale with the number of inelastic nucleon-nucleon collisions and don't exhibit the strong suppression observed for charged hadrons and neutral pions. This observation is consistent with models which attribute the suppression of high-pT hadrons to energy loss of quarks and gluons in the hot and dense medium produced in Au+Au collisions at RHIC.