Charmonium suppression - Interplay of hadronic and partonic degrees of freedom

Last year the E866-group of the Fermilab measured the cursive Greek chi_F dependence of J/Ψ and Ψ′ suppression in pA collisions. We discuss two of the effects found in that experiment with regard to color coherence effects: the different suppression of the J/Ψ and the Ψ′ at cursive Greek chi_F < 0 and the significant suppression of both at large cursive Greek chi_F. The small cursive Greek chi_F regions is dominated by fully formed charmonium states and thus enables us to discuss the formation time and the cross section of the different charmonium states. In the large cursive Greek chi_F region the interaction of the charmonium states with nuclear matter has to be described by partonic degrees of freedom, because in that kinematic domain the formation time is much larger than the nuclear radii. The understanding of this region will be crucial for the interpretation of the data of the future heavy ion colliders RHIC and LHC.