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A-Dependence of Heavy Flavour Production in QCD

We calculate the A-dependence of charm and beauty production cross sections on nuclear targets taking into account the difference of quark and gluon distributions in free nucleons and in nucleus. At comparatively low energies, if $σ\sim A^α$, the value of $α$ is slightly higher than unity. With the growth of the initial energy the value of $α$ decreases and becomes smaller than unity. We also calculate the values of $α$ for different Feynman-$x$ of the produced $Q\overline{Q}$ pair and obtain that they decrease significantly in the beam fragmentation region.