xF-dependence of J/Ψ suppression in pA collisions

Coherence effects are important in the description of collisions with extended objects as nuclei. At fixed target energies and small xF, the coherence length of the fluctuation containing the cc̄ is small and the usual nuclear absorption model is valid. However, at higher energies and/or xF the nucleus is seen as a whole by the fluctuation. In this case, the total, not the absorptive, cc̄−N cross section controls the suppression and also shadowing of gluons appears. We propose that the growth of the coherence length can explain the xF-dependence of present experimental data. For this, we need a ratio of absorptive over total cc̄−N cross section of 0.2.