Photons from Pb-Pb collisions at ultrarelativistic energies

Abstract

High energy photon emission rate from matter created in Pb+Pb collisions at CERN SPS energies is evaluated. The evolution of matter from the initial state up to freeze-out has been treated within the framework of (3+1) dimensional hydrodynamic expansion. We observe that the photon spectra measured by the WA98 experiment are well reproduced with hard QCD photons and photons from a thermal source with initial temperature $\ensuremath{\sim}200\mathrm{MeV}.$ The effects of the spectral changes of hadrons with temperature on the photon emission rate and on the equation of state are studied. Photon yield for Au+Au collisions at RHIC energies is also estimated.