A DEPENDENCES OF THE CROSS-SECTIONS FOR HARD PROCESSES IN QCD

The A dependences of the cross sections for heavy-quark production, as well as those for the production of Drell-Yan lepton pairs, are compu ted with allowance for distinctions between parton distributions in fr ee and bound nucleons. This is done for both proton-nucleus and nucleu s-nucleus collisions. If the resulting cross sections are parametrized as sigma similar to A(alpha), the values of alpha for heavy-quark pro duction at moderately low energies prove to be slightly greater than u nity. With increasing initial energy, the exponent alpha decreases mon otonically down to values that are less than unity. It is also shown t hat alpha is a function of the Feynman variable x(F) of the product <Q (Q)over bar> or l(+)l(-) pair. The sensitivity of these results to the set of parton distributions that is used in the present study is disc ussed.