Enhanced Direct Photon Production in Au+Au Collisions at 200 GeV in PHENIX

TL;DR

This paper reports the measurement of direct photon production in 200 GeV Au+Au collisions at RHIC, showing an enhancement over scaled p+p results and consistent with hot, dense medium formation models.

Contribution

It provides the first evidence of enhanced direct photon yield in Au+Au collisions at RHIC energies, supporting the formation of a hot quark-gluon plasma.

Findings

Significant excess of low-mass electron pairs in Au+Au collisions.

Enhanced direct photon yield compared to scaled p+p collisions.

Results consistent with hydrodynamical models of hot medium formation.

Abstract

The production of electron pairs with transverse momentum between 1 and 5 GeV/c and m< 300 MeV has been measured at mid-rapidity in 200 GeV p+p and Au+Au collisions by the PHENIX experiment at RHIC. A significant excess above the hadronic background was observed in both p+p and Au+Au collisions. Treating the excess as internal conversion of direct photons, the direct photon yield in Au+Au was found to be enhanced compared to the binary-scaled p+p yield. The enhancement is consistent with an exponential inverse slope of 221 +- 23 +- 18 MeV and predictions from hydrodynamical models with initial temperature between 300 and 600 MeV at formation times of 0.6-0.15 fm/c.