Leading-particle effect from heavy-quark recombination.

The leading particle effect in charm hadroproduction is an enhancement of the cross section for a charmed hadron D in the forward direction of the beam when the beam hadron has a valence parton in common with the D. The large D(+)/D(-) asymmetry observed by the E791 experiment is an example of this phenomenon. We show that the heavy-quark recombination mechanism provides an economical expla-nation for this effect. In particular, the D(+)/D(-) asymmetry can be fit reasonably well using a single parameter whose value is consistent with a recent determination from charm photoproduction.