Direct Photon Production in 158 A GEV 208PB+208PB Collisions

A measurement of direct photon production in ²⁰⁸Pb+²⁰⁸Pb collisions at 158 A GeV has bee carried out in the CERN WA98 experiment. The invariant yield of direct photons in central collisions is extracted as a function of transverse momentum in the interval 0.5 < p_T < 4 GeV/c. A significant direct photon signal, compared to statistical and systematical errors, is seen at p_T > 1.5 GeV/c. The results constitute the first observation of direct photons in ultrarelativistic heavy-ion collisions which could be significant for diagnosis of quark gluon plasma formation.