RESCATTERING EFFECTS IN HEAVY FLAVOR PRODUCTION OFF NUCLEI

The absorptive corrections resulting from the rescattering of a heavy flavour (the so-called nuclear absorption) are usually calculated with a probabilistic formula valid only in the low energy limit. We extend this formula to all energies using a quantum field theoretical approa ch. For charmonium and bottonium we find that the absorptive correctio ns in the rigorous treatment are very similar to the ones in the proba bilistic approach. On the contrary, at sufficiently high energy, open charm and bottom are absorbed as much as charmonium and bottonium - in spite of the fact that their absorptive cross-sections are zero, and therefore they are not absorbed in the probabilistic model. At high en ough energies there are also absorptive corrections due to the shadowi ng of the nucleus structure function, which are present for all system s including Drell-Yan pair production. These shadowing corrections can cel in the low energy limit.