Quarkonium production and suppression in Pb+Pb and p+A collisions at SPS energies

We present the results on charmonium production as measured by experiment NA50 at the CERN-SPS in p+A and Pb+Pb collisions. The J/ψ / Drell-Yan and ψ′ / Drell-Yan cross-section ratios as a function of centrality are obtained from Pb+Pb data samples collected at 158 GeV per nucleon in the 1998 run and, under improved experimental conditions, in 2000. The recent very high precision NA50 proton-nucleus results allow to determine the J/ψ nuclear absorption only from proton induced reactions, and to calculate the expected J/ψ yield in Pb+Pb collisions at 158 GeV. The J/ψ expected production obtained in this way is compared to the NA50 results in Pb+Pb collisions, as well as to the NA38 results for S+U reactions.