Study of the Decay $\Lambda_c \to \Lambda l^+ \nu_{l}

Using the CLEO II detector at CESR, we observe 500 $\Lambda l^+$ pairs consistent with the semileptonic decay $\Lambda_c \to \Lambda l^+ \nu_{l}$. We measure $\sigma (e^+ e^- \to \Lambda_c X) \dot {cal B}(\Lambda_c^+ \to \Lambda l \nu_{l}) =4.77 \pm 0.25 \pm 0.66$pb. Combining with the charm semileptonic width and the lifetime of the $\Lambda_c$, we also obtain ${\cal B}(\Lambda_c \to p K^- \pi^+)$. We find no evidence for $\Lambda l^+ \nu_{l}$ final states in which there are additional $\Lambda_c^+$ decay products. We measure the decay asymmetry parameter of $\Lambda_c \to \Lambda l^+ \nu_{l}$ to be $\alpha_{\Lambda_c} =-0.89\pm{^{0.17}_{0.11}}\pm{^{0.09}_{0.06}}.