The preliminary results for the single-photon spectrum obtained by the WA80 collaboration are analyzed. The data are well described by a scenario where a thermalized quark-gluon plasma is formed initially, which expands, cools, hadronizes, and undergoes a freeze-out. It is also seen that the data do not seem to favor the scenario where the matter is initially formed in a hot hadronic phase, which cools and undergoes freeze-out and does not involve a phase transition.

• Received 29 April 1994

DOI:https://doi.org/10.1103/PhysRevLett.73.2421