The evolution of cross section ratio ψ′/J/ψ from p-A to S-U interactions. Direct photon emission in correlation with φ and J ψ

J ψ and ψ′ production cross sections are studied for several proton induced reactions and in SU collisions, in the NA38 experiment, by measuring the resonances' decays in the muon pair channel. Whereas in p-A interactions the ψ′/J/ψ ratio remains constantin going from p-p and p-d collisions to p-W and p-U, with a mean value of 1.76% ± 0.04%, in the SU data it exhibits half of this value and decreases as centrality of the collision increases. Also studied are the differences between the γ π⁰ ratio yields correlated with the J ψ mass range and other dimuon masses; no significant effect is seen.