Heavy Ion Tea

Direct Photons from STAR
Martijn Russcher (Utrecht University)

Abstract: Direct photons are a very clean probe of the matter which is formed in ultra-relativistic heavy-ion collisions. They leave the medium without any further interaction and therefore allow for a study of the earliest stages of the collision. Direct photon production in p+p is a precision test of perturbative QCD and it can be used in d+Au to study initial state effects in the gold nucleus. Both measurements are essential to interpret the results from Au+Au collisions at RHIC. A study of mid-rapidity direct photon and neutral pion production in d+Au and p+p collisions will be presented. The results have been obtained with the Barrel Electro-Magnetic Calorimeter from STAR and will be compared to a pQCD calculation.