Speaker
Description
Direct photons are a very important probe to study the properties of the medium created by heavy ion collisions, since they are produced throughout the collision history and carry out information about the medium at the point of their production, without strong interaction. While high pT direct photons originating from initial hard scattering serve as a test for pQCD, low pT photons contain rich information about a hot and dense QCD medium produced in the collisions. In particular, thermal photons are of keen interest since they allow us to direct access to the thermodynamic properties of the medium. Their contribution is expected to be very large typically below 3GeV/c . PHENIX has observed for the first time an enhanced yield below 3GeV/c in Au+Au as expected, but v2 of the enhanced yield is unexpectedly large. The mechanism to produce a large direct photon yield with a large v2 is not understood yet. PHENIX has made systematic measurements of direct photons with different collision energies and species. These systematic measurements could help understand photon production mechanism in the hot QCD medium. In this presentation, we will report the latest status of the direct photon measurements.
