image absorption in heavy ion collisions II Original Research Article

Using the methods introduced in a previous paper, we consider the dissociation of J/ψ by the lowest-lying pseudoscalar and vector mesons in the hadronic fireball formed in heavy ion collisions, assumed to be a hadron gas at temperature T. Absorption by nuclear matter is accounted for as well. We compare with the S–U and Pb–Pb data presented by the NA50 Collaboration. From data at low centrality we find T=165–185 MeV, close to the predicted temperature of the transition to quark–gluon plasma and to the temperatures measured by hadron abundances. We extrapolate to higher centralities with the approximation of scaling the energy density of the fireball with the average baryon density per unit transverse area. Using the energy–temperature relation of the hadron gas made by the same pseudoscalar and vector mesons, the fall off of J/ψ production shown by the NA50 data can be marginally reproduced only for the highest temperature, T0=185 MeV. If we use the energy–temperature relation of a Hagedorn gas with limiting temperature TH=180 MeV, predictions fall short from reproducing the data. These results suggest that a different mechanism is responsible for the J/ψ suppression at large centralities, which could very well be the formation of quark–gluon plasma.