NUCLEAR SHADOWING EFFECTS ON CHARMONIUM PRODUCTION IN QCD

It is shown that the effects on charmonium production of the modification of nucleon parton distributions inside nuclei are similar in the factorization approach based on nonrelativistic QCD and in the color evaporation model. In the first model, a separate study of the color octet and color singlet contributions to the yields of the various charmonium states as well as the contributions of these states to the total J/ψ production is performed. It is found that a clear x_F dependence of these contributions which, together with an overall normalization given by absorption of the pre-resonant state inside the nuclear medium, can reproduce experimental data a for moderate x_F. However, at large x_F, there is bigger suppression that cannot be fit by this overall normalization together with the shadowing of structure functions.