Hard Processes on Nuclear Targets in Qcd

We calculate the A-dependence of open charm and beauty as well as DrellYan pair production cross sections on nuclear targets taking into account the difference of quark and gluon distributions in free and bound nucleons. The results are presented for both proton-nucleus and nucleus-nucleus collisions. For the case of heavy flavour production at comparatively low energies, if σ ∼ Aα, the values of α are slightly higher than unity. With increasing energy α decreases in all cases and becomes smaller than unity. We also show α as a function of Feynman-x of the produced QQ or l+l− pair and obtain that it decreases significantly in the beam fragmentation region. The sensitivity of our results to the used set of parton distributions is also discussed. September 1996 hep-ph/9609296 US-FT/37-96