Gluon shadowing in heavy flavor production off nuclei

Abstract

Gluon shadowing which is the main source of nuclear effects for production of heavy flavored hadrons, remains unknown. We develop a light-cone dipole approach aiming at simplifying the calculations of nuclear shadowing for heavy flavor production, 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 ̄ c pair. It is about twice as large as in DIS [B.Z. Kopeliovich et al., Phys. Rev. D 62 (2000) 054022], but smaller than for charmonium production [B.Z. Kopeliovich et al., Nucl. Phys. A 696 (2001) 669]. The higher twist shadowing correction related to a nonzero size of the c ̄ c 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 [PHENIX Collaboration, K. Adcox et al., nucl-ex/0202002]. 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 .