J/psi and psi ' production in p, O and S induced reactions at SPS energies

The production of the J/psi and psi' charmonia states has been studied, thr ough their dimuon decay, in proton, Oxygen and Sulphur induced reactions, b y the NA38 experiment at the ERN SPS. The proton data was collected with be ams of 200 and 450 GeV, while the ion beams had an energy of 200 GeV per in cident nucleon. The J/psi production cross-section per nucleon-nucleon coll ision exhibits a remarkably continuous pattern, as a function of the produc t of the mass numbers of the interacting nuclei, from pp up to S-U reaction s. The same pattern is observed within S-U collisions, as a function of the collision centrality. While in p-A interactions both charmonia states exhi bit the same A-dependence, in S-U collisions the psi' production is very st rongly suppressed. (C) 1999 Published by Elsevier Science B.V. All rights r eserved.