High Precision J/psi and Upsilon-production data and the Nuclear Glue

We use the high statistics E-772 data on the nuclear dependence of the production of quarkonia $(J/\psi$ and $\Upsilon)$ and dimuons at large transverse momentum $(p_T)$ in $p$-$A$ collisions to get information about the gluonic EMC effect. We find a satisfactory quantitative agreement of the theoretical predictions with the data although none of the models of the EMC effect we consider could account for the entire data. Since all the qualitative features are understood none the less in terms of perturbative QCD with nuclear dependent parton densities, our results suggest that these data can now be used for a better determination of the nuclear parton densities. Our conslusions are shown to be insensitive to the hadronisation mechanism for the quarkonia.