Charmonia production at SPS energies

Abstract

We present the final results of experiment NA50 on charmonia production in Pb-Pb interactions at 158 A GeV. A strong increasing suppression is observed with increasing centrality, for both the J/ψ and ψ ′ resonances. We also present new developments regarding the J/ψ and ψ ′ normal nuclear absorption determinations deduced from proton-nucleus data only. Their comparison with Pb-Pb results allows us to conclude that the J/ψ anomalous suppression sets in at mid-centralities while the S-U results show a reasonable agreement with the p-A behavior. The ψ ′ suffers a significantly stronger suppression already in S-U interactions, which continuously increases in the Pb-Pb system, and is completely incompatible with the expected behavior deduced from p-A collisions.