The study of the Cabibbo-favored semileptonic decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{e}^{+}{\nu }_e$ is reported using a $4.5{\mathrm{fb}}^{-1}$ data sample of $e^{+}{e}^{-}$ annihilations collected at center-of-mass energies ranging from 4.600 GeV to 4.699 GeV with the BESIII detector at the BEPCII collider. The branching fraction of the decay is measured to be $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{e}^{+}{\nu }_e)=(3.56\pm 0.11_{\mathrm{stat}}\pm 0.07_{\mathrm{syst}})\%$, which is the most precise measurement to date. Furthermore, we perform an investigation of the internal dynamics in ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{e}^{+}{\nu }_e$. We provide the first direct comparisons of the differential decay rate and form factors with those predicted from lattice quantum chromodynamics (LQCD) calculations. Combining the measured branching fraction with a $q^2$-integrated rate predicted by LQCD, we determine $|V_{cs}|=0.936\pm 0.017_{\mathcal{B}}\pm 0.024_{\mathrm{LQCD}}\pm 0.007_{{\tau }_{{\mathrm{\Lambda }}_c}}$.

• Received 28 July 2022
• Accepted 1 November 2022

DOI:https://doi.org/10.1103/PhysRevLett.129.231803

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Published by the American Physical Society