Latest results from NA50 on J/ψ suppression in Pb-Pb collisions at 158 GeV/c

The main goal of the NA50 experiment is to study the J/psi suppression pattern in Pb-Pb interactions, at 158 GeV/c per nucleon at the CERN SPS, We present here the results from the 1996 and 1998 data taking periods. We used new event selection procedures, different analysis techniques and different event centrality estimators and we can now confirm and extend our preavious observation that the J/psi is anomalously suppressed when going from peripheral to central Pb-Pb collisions. We observe that in peripheral collisions the J/psi cross section per nucleon-nucleon collision agrees with the pattern inferred from a wide range of measurements with lighter systems, from p-p to S-U. When the collisions become more central a clear departure from this behaviour is observed. The 1996 data show a sudden drop in the J/psi production yield for transverse energy values above 40 GeV. The 1998 data provide a big improvement in the study of the most central region, where a second change in the pattern becomes visible. This suppression pattern is confirmed by an independent analysis which uses the zero degree energy (E-ZDC) as centrality estimator.