  When studying the initial state and evolution of the matter created in
relativistic heavy ion collisions, high-pT direct photons are a powerful probe.
They are created in initial hard processes and in parton fragmentation, and
possibly in interactions of partons with the hot and dense medium. We present
systematic measurements of high-pT direct photon production in \sqrt{s_{NN}} =
200 GeV p+p and Au+Au collisions. The nuclear modification factor of direct
photons is shown for 5 < pT < 18 GeV/c, and at very high transverse momenta it
seems to be below unity in the most central Au+Au collisions.
