Inclusive charm production in Υ(nS) decay

Based on the nonrelativistic QCD (NRQCD) factorization formalism, we calculate the inclusive charm production rate in Υ(nS) decay at leading order in the strong coupling constant αs and the relative velocity v of the b quark in the quarkonium rest frame. The branching fractions for Υ(nS) to charm for n=1, 2, and 3 are all around 7%-9%. About 60% of the branching fraction into charm is from annihilation of the color-singlet bb̄ pair into γ*→cc̄. Most of the remaining branching fraction is from annihilation of the color-singlet bb̄ pair decaying into cc̄gg. We also compute the momentum distributions of the charm quark and charmed hadrons in the decays. The virtual-photon contribution to the charm-quark momentum distribution is concentrated at the end point while the cc̄gg contribution is broad. The momentum distributions for charmed hadrons are obtained by convolving the charm-quark momentum distribution with charm fragmentation functions. This makes the momentum distributions for charmed hadrons softer than that for the charm quark. This effect is particularly significant in the virtual-photon contribution.