THERMAL PARTICLE AND PHOTON PRODUCTION IN PB+PB COLLISIONS WITH TRANSVERSE FLOW

Particle and photon production is analyzed in the presence of transver se flow using two approximations to describe the properties of the had ronic medium, one containing only pi,rho,omega, and eta mesons (simpli fied equation of state) and the other containing hadrons and resonance s from the particle data table. Both are considered with and without i nitial quark gluon plasma formation. In each case the initial temperat ure is;fixed by requiring dN(ch)/dy similar to 550 in the final state. It is shown that most observables are very sensitive to the equation of state. This is particularly evident when comparing the results of t he simplified equation of state in the scenarios with and without phas e transition. The hadronic gas scenario leads to a substantially highe r rate for the p(T) distribution of all particles. In the complete equ ation of state with several hundreds of hadronic resonances, the diffe rence between the scenarios with and without phase transition is rathe r modest. Both photon and particle spectra, in a wide p(T) range, show very similar behavior. It is therefore concluded that from the p(T) s pectra it will be hard to disentangle quark gluon plasma formation in the initial state. It is to be stressed, however, that there are conce ptual difficulties in applying a pure hadronic gas equation of state a t SPS energies. The phase transition scenario with a quark gluon plasm a present in the initial state seems to be the more natural one.