Direct Photon Production in 158 A GeV $^{208}$ PB+$^{208}$ PB Collisions

A measurement of direct photon production in Pb+Pb collisions at 158 AGeV has been 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 < pT < 4 GeV/c. A significant direct photon signal, compared to statistical and systematical errors, is seen at pT > 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.