PHENIX measurements of low momentum direct photons from large ion collisions as a function of beam energy and system size

Abstract

PHENIX has discovered a large yield of low momentum direct photons along with a large azimuthal anisotropy in Au+Au collisions at sNN=200GeV. The large yield suggests early emission at high temperature, while the large anisotropy points towards late emission when the radial flow of the matter is fully developed, but the temperature is already reduced. This apparent contradiction poses a significant challenge to models that aim to calculate thermal photon production. To further constrain the sources of the low pT photons, PHENIX has analyzed data from Au+Au collisions at lower beam energies of 62.4 and 39 GeV, as well as data from smaller Cu+Cu collision system at 200 GeV. Here we present the first preliminary results from these analyses.