Inclusive Lambda_c Production in e^+e^- Annihilations at sqrt{s}=10.54 GeV and in Upsilon(4S) Decays

Abstract

We present measurements of the total production rates and momentum distributions of the charmed baryon ${\Lambda }_c^{+}$ in $e^{+}{e}^{-}\to$ hadrons at a center-of-mass energy of 10.54 GeV and in ${\rm Y}(4S)$ decays. In hadronic events at 10.54 GeV, charmed hadrons are almost exclusively leading particles in $e^{+}{e}^{-}\to c\bar{c}$ events, allowing direct studies of $c$-quark fragmentation. We measure a momentum distribution for ${\Lambda }_c^{+}$ baryons that differs significantly from those measured previously for charmed mesons. Comparing with a number of models, we find none that can describe the distribution completely. We measure an average scaled momentum of $⟨x_p⟩=0.574\pm$0.009 and a total rate of $N_{\Lambda c}^{q\bar{q}}=0.057\pm$0.002(exp.)$\pm$0.015(BF) ${\Lambda }_c^{+}$ per hadronic event, where the experimental error is much smaller than that due to the branching fraction into the reconstructed decay mode, $p{K}^{-}{\pi }^{+}$. In ${\rm Y}(4S)$ decays we measure a total rate of $N_{\Lambda c}^{{\rm Y}}=0.091\pm$0.006(exp.)$\pm$0.024(BF) per ${\rm Y}(4S)$ decay, and find a much softer momentum distribution than expected from B decays into a ${\Lambda }_c^{+}$ plus an antinucleon and one to three pions.

16 pages, 10 postscript figues, version published in Phys. Rev. D with minor changes to text and some figs