Charm-anticharm asymmetries in photoproduction from heavy-quark recombination

The asymmetries between charm and anticharm mesons observed in fixed-target photoproduction experiments are an order of magnitude larger than the asymmetries predicted by conventional perturbative QCD. We show that these charm meson asymmetries can be explained by a heavy-quark recombination mechanism for heavy meson production. In this process, a charm quark combines with a light antiquark from the hard-scattering process and they subsequently hadronize into a state including the charm meson. This recombination mechanism can be calculated within perturbative QCD up to some nonperturbative constants. After using symmetries of QCD to reduce the number of free parameters to two, we obtain a good fit to all the data on the asymmetries for charmed mesons from the E687 and E691 experiments.