Thermal photon production in high-energy nuclear collisions.

We use a boost-invariant one-dimensional (cylindrically symmetric) fluid dynamics code to calculate thermal photon production in the central rapidity region of S+Au and Pb+Pb collisions at SPS energy ([radical][ital s] =20 GeV/nucleon). We assume that the hot matter is in thermal equilibrium throughout the expansion, but consider deviations from chemical equilibrium in the high temperature (deconfined) phase. We use equations of state with a first-order phase transition between a massless pion gas and quark gluon plasma, with transition temperatures in the range 150[le][ital T][sub [ital c]][le]200 MeV.