Observation of Direct Photons in Central 158 A GeV 208Pb+208Pb Collisions

Abstract

A measurement of direct photon production in 208Pb + 208Pb collisions at 158 A GeV 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 < 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.

5 pages, 3 figures, submitted to Physical Review Letters

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