EQUATION OF STATE OF HADRONIC MATTER AND ELECTROMAGNETIC-RADIATION FROM RELATIVISTIC HEAVY-ION COLLISIONS

We study the radiation of thermal photons and dileptons likely to be p roduced in relativistic heavy ion collisions. We find that the thermal photon multiplicity scales with the charged pion multiplicity(dN(ch)/ dy) as (dN(ch)/dy)(alpha) with alpha similar to 1.2 for a transversely expanding system, contrary to the general belief of a quadratic depen dence. The scaling is shown to be valid, both for real and virtual pho tons. The coefficient of proportionality at a given energy shows, howe ver, strong dependance on the equation of state of hot hadronic matter produced in such collisions. (C) 1998 Elsevier Science B.V.