Gluon Shadowing and Heavy Flavor Production off Nuclei

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Abstract
Gluon shadowing is the main source of the expected nuclear effects for production of heavy flavored hadrons. We develop a light-cone dipole approach aiming at simplifying the calculations of nuclear effects, as well as the cross section which does not need next-to-leading and higher order corrections. A substantial process dependence of gluon shadowing is found at the scale of charm mass manifesting a deviation from QCD factorization. The magnitude of the shadowing effect correlates with the symmetry properties and color state of the produced c-cbar pair. It is about twice as large as in DIS, but smaller than for charmonium production. The higher twist shadowing correction related to a nonzero size of the c-cbar pair is not negligible and steeply rises with energy. We predict an appreciable suppression by shadowing for charm production in heavy ion collisions at RHIC and a stronger effect at LHC. At the same time, we expect no visible difference between nuclear effects for minimal bias and central collisions, as is suggested by recent data from the PHENIX experiment at RHIC. We also demonstrate that at medium high energies when no shadowing is possible, final state interaction may cause a rather strong absorption of heavy flavored hadrons produced at large x_F.

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