A Circumstantial Evidence for the Possible Production of QGP in the 158A GeV/c Central Pb+Pb Collisions

Abstract

Hadron and string cascade model (JPCIAE) with the hypothesis without introducing the quark-gluon plasma (QGP), is employed to study the direct photon and $π^0$ transverse momentum distributions for central $^{208}$Pb+$^{208}$Pb collisions at 158A GeV/c . JPCIAE model, is based on LUND model, especially on the envent generator PYTHIA, and can be used to simulate the relativistic nucleus-nucleus collisions where PYTHIA is called to deal with hadron-hadron collisions. In our work, the theoretical results of transverse momentum distribution for both the direct photon and the $π^0$ particle are lower than the data of WA98 experiment. However, JPCIAE model can ever explain successfully the results of WA80 and WA93 experiments of central S+Au collisions at 200A GeV/c where no evidence of direct photon excess. Having considered the results of WA80 and WA93 experiments can be explained but WA98's can't, that might provide a circumstantial evidence for the possible production of QGP in the high-energy central Pb+Pb collisions.