xF-dependence of J/Ψ suppression in pA collisions.

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