Direct photon production in high-energy heavy-ion collisions

Direct thermal photons in the p(t) range of 0 - 5 GeV/c are expected to provide a sensitive probe of the hot dense matter formed in the early stage of relativistic heavy ion collisions. The production of single photons in 158 AGeV Pb+Pb interactions has been studied with the 10080 detector lead glass calorimeter of the WA98 experiment at CERN. Neutral pi(0) cross section has been measured via its two-photon decay branch. At pt >=similar to 1GeV/c single photon yields of similar to 20% of the decay photon yields are observed consistently with different photon identification criteria both for the peripheral and central events.