Observation of Charmed-Baryon Production ine+e−Annihilation

A peak in the $p{K}^{-}{\pi }^{+}$ and $\overline{p}{K}^{+}{\pi }^{-}$ invariant-mass spectra at 2.285±0.006 GeV/${\mathit{c}}^2$ is observed, which is associated with the lowest-lying charmed baryon (${\Lambda }_c$). A cross section times branching ratio of 0.037±0.012 nb at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=5.2\mathrm{}$ GeV is measured with a substantial fraction of the events produced with an equal recoiling mass. New measurements of inclusive $p$ and $\Lambda$ cross sections are also presented, allowing an estimate of the branching ratio $B({\Lambda }_c\to p{K}^{-}{\pi }^{+})=0.022\mathrm{}\pm 0.010$.