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

We present measurements of the total production rates and momentum distributions of the charmed baryon $Λ_c^+$ in $e^+e^- \to$ hadrons at a center-of-mass energy of 10.54 GeV and in $Υ(4S)$ 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 $Λ_c^+$ 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 $\left< x_p \right> = 0.574\pm$0.009 and a total rate of $N_{Λc}^{q\bar{q}} = 0.057\pm$0.002(exp.)$\pm$0.015(BF) $Λ_c^+$ per hadronic event, where the experimental error is much smaller than that due to the branching fraction into the reconstructed decay mode, $pK^-π^+$. In $Υ(4S)$ decays we measure a total rate of $N_{Λc}^Υ = 0.091\pm$0.006(exp.)$\pm$0.024(BF) per $Υ(4S)$ decay, and find a much softer momentum distribution than expected from B decays into a $Λ_c^+$ plus an antinucleon and one to three pions.

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