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

TL;DR

This paper measures the production rates and momentum distributions of Lambda_c+ baryons in electron-positron collisions at 10.54 GeV and in Upsilon(4S) decays, revealing differences from meson distributions and challenging existing models.

Contribution

It provides the first detailed measurements of Lambda_c+ production and momentum spectra in these processes, highlighting discrepancies with theoretical models.

Findings

Lambda_c+ production rate in hadronic events is 0.057 per event.

Average scaled momentum <x_p> is 0.574.

Lambda_c+ momentum distribution is softer 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 $\Upsilon(4S)$ 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 $\left< x_p \right> = 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, $pK^-\pi^+$. In $\Upsilon (4S)$ decays we measure a total rate of $N_{\Lambda c}^{\Upsilon} = 0.091\pm$0.006(exp.)$\pm$0.024(BF) per $\Upsilon(4S)$ 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.