Transverse momentum of $\text{J}\text{ψ}$ produced in pCu, pU, ¹⁶OCu, ¹⁶OU and ³²SU collisions at 200 GeV per nucleon

Muon pairs produced in PbPb interactions at 158 GeV/c per nucleon and in p-A interactions at 400 GeV/c, together with older S-U results obtained at 200 GeV/c are used to study the transverse momentum and transverse mass distributions of the J/Ψ.

Muon pairs produced in Pb–Pb interactions at 158 GeV/c per nucleon are used to study the transverse momentum distributions of the J/ψ, ψ′ and dimuons in the mass continuum. In particular, the dependence of these distributions on the centrality of the Pb–Pb collision is investigated in detail.

In recent years, the J/ψ signal in heavy-ion collisions at the CERN SPS has attracted much attention as a potential quark–gluon plasma signature. This review discusses the prediction of J/ψ suppression and the systematics of this signature as a function of the transverse energy of the collision and the transverse momentum of the J/ψ. Since J/ψ suppression was already present in hadron–nucleus interactions, hadronic models of absorption by nucleons and scattering with comoving secondaries soon emerged. After a discussion of J/ψ and other related production data in $\text{pp,}\text{pA}$, and AB interactions, hadronic suppression models are introduced and compared with the CERN SPS data. Plasma model predictions are also given for CERN SPS collisions as well as for the future RHIC and LHC heavy-ion colliders.

The NA50 collaboration has measured J/ψ, ψ′ and Drell Yan pair production in PbPb interactions at 158 GeV/c per nucleon at the CERN SPS. Final results from the 1995 run and preliminary ones from the higher statistics 1996 run are presented.

A anomalous J/ψ suppression (relative to the Drell-Yan process) has been observed with respect to the suppression pattern established in experiments NA38 and NA51 with proton, oxygen and sulfur beams. The 1996 data allow a detailed study of the suppression pattern in the PbPb sample itself, showing a discontinuity around an E_T value (the neutral transverse electromagnetic energy) of 50 GeV. The ψ′ is also suppressed relative to Drell-Yan, with a pattern very similar to the one observed in SU collisions. Finally, the p_T distributions of dimuons are presented. The average p_T² of the J/ψ in PbPb collisions does not increase any more with E_T above 100 GeV.

A reexamination of hadronic comover scattering indicates that this mechanism cannot explain the observed ψ suppression in Pb+Pb interactions. The possibility of quark-gluon plasma formation is therefore considered.

We have studied the production of J/ψ, ψ′ and prompt muon pairs in the mass continuum from a sample of sulfur-uranium interactions at 200 GeV/c per nucleon. We report, in this letter, results obtained for the transverse momentum distributions and their dependence on the transverse energy released in the collision, used as an estimator of the centrality of the nucleus-nucleus interaction.