Excess pions in Drell-Yan and deep inelastic scattering experiments

Recent data on Drell-Yan processes induced by protons on nuclear targets gives non trivial information about nuclear effects. A very simple model for excess pions in nuclei reproduces the main features of these data, and also of those coming from deep inelastic experiments. This simple scheme gives an unified treatment of nuclear effects highlighting its importance in the deuteron and provides a precise prediction for future p - p and p - d Drell-Yan experiments. (orig.)