Probabilistic versus Field-theoretical Description of Heavy Flavour 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 approach. For charmonium and bottonium we find that the absorptive corrections in the rigorous treatment are very similar to the ones in the probabilistic 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 enough energies there are also absorptive corrections due to the shadowing of the nucleus structure function, which are present for all systems including Drell-Yan pair production. These shadowing corrections cancel in the low energy limit. a Work supported by INTAS 93-79. b Permanent address: Department of High-Energy Physics, University of St. Petersburg, St. Petersburg, 198904 Russia. c Now at II. Institut für Theoretische Physik, Universität Hamburg, Luruper Chaussee 149, D-22761, Germany. d Laboratoire associé au Centre National de la Recherche Scientifique URA D0063.