A-DEPENDENCE OF HEAVY FLAVOR PRODUCTION IN QCD

We calculate the A-dependence of charm and beauty production cross sec tions on nuclear targets taking into account the difference of quark a nd gluon distributions in free nucleons and in the nucleus. At compara tively low energies, if sigma similar to A(alpha), the value of alpha is slightly higher than unity. With the growth of the initial energy t he value of alpha decreases and becomes smaller than unity. We also ca lculate the values of alpha for different Feynman-x of the produced <Q (Q)over bar> pair and obtain that they decrease significantly in the b eam fragmentation region.