11th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions

PHENIX presents the simultaneous measurement of high pt (8-18 GeV/c) direct γ and π0 production in d+Au collisions at 200 GeV. The analysis is performed for different events samples selected by event activity. The direct γ-to-π0 ratio is independent of event activity, except for events with the highest activity where the ratio is slightly enhanced. Final state effects are expected to be small for direct photons and initial state effects are expected to be similar for direct γ and π0. Therefore, the new PHENIX results suggest that π0 production is suppression in the final state of the most central d+Au collisions. Expressed as nuclear modification factor RxA, this suppression is about 20%. Here RxA is determined in a model independent way, by quantifying the effective number of binary collisions from the ratio of direct photons measured in d+Au compared to p+p collisions. To establish if the suppression is linked to energy loss, PHENIX is currently analyzing p+Au and 3He+Au collisions. In this talk the latest results will be presented.