UC Berkeley

We present measurements of the total production rates and momentum distributions of the charmed baryon Λc+ in e+e-→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-→cc̄ events, allowing direct studies of c-quark fragmentation. We measure a momentum distribution for Λc+ 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 xp=0.574±0.009 and a total rate of NΛcqq̄=0.057±0.002(exp.)±0.015(BF)Λc+ 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 NΛcΥ=0.091±0. 006(exp.)±0.024(BF) per Υ(4S) decay, and find a much softer momentum distribution than expected from B decays into a Λc+ plus an antinucleon and one to three pions. © 2007 The American Physical Society.