Inclusive Λ+c production in e+e− annihilations at √s=10.54  GeV and in Υ(4S) decays

We present measurements of the total production rates and momentum distributions of the charmed baryon Λ + c in e + e − → hadrons at a center-of-mass energy of 10.54 GeV and in Υ ( 4 S ) decays. In hadronic events at 10.54 GeV, charmed hadrons are almost exclusively leading particles in e + e − → c ¯ 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 ⟨ x p ⟩ = 0.574 ± 0.009 and a total rate of N q ¯ q Λ c = 0.057 ± 0.002 ( exp  . ) ± 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, p K − π + . In Υ ( 4 S ) decays we measure a total rate of N Υ Λ c = 0.091 ± 0.006 ( exp  . ) ± 0.024 ( BF ) per Υ ( 4 S ) 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