Abstract : In the framework of the experimental research for the quark and gluons plasma formation in ultrarelativistic heavy ion collisions, data obtained by the NA50 collaboration at SPS-CERN are analysed. The segmented target used by NA50 experiment is described and analysed in terms of vertex identification efficiency and reinteractions recognition. The absolute J/Psi, Psi' and Drell-Yan process cross-sections in 158 GeV/c per nucleon Pb-Pb interactions are extracted. The transverse energy dependence of the production yield of J/Psi and Drell-Yan process is established. The comparison of these cross-sections with the ones measured in lighter systems and the comparison of the E_T dependence of J/Psi production with the Glauber model prediction show an anormalous J/Psi suppression which depends of the centrality of the collisions. The anomalous suppression observed in Pb-Pb interactions is confronted to theorical models proposed by several authors, describing charmonium bound states formation and interactions in confined or deconfied media.