The study of the Cabibbo-favored semileptonic decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{\mu }^{+}{\nu }_{\mu }$ is reported using $4.5{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected at center-of-mass energies ranging from 4.600 to 4.699 GeV. The branching fraction of the decay is measured to be $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{\mu }^{+}{\nu }_{\mu })=(3.48\pm 0.14_{\mathrm{stat}}\pm 0.10_{\mathrm{syst}})\%$, 3 times more precise than the prior world average result. Tests of lepton flavor universality using ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{\ell }^{+}{\nu }_{\ell }$ ($\ell =e$, $\mu$) decays are reported for the first time, based on measurements of the differential decay rates and the forward-backward asymmetries in separate four-momentum transfer regions. The results are compatible with Standard Model predictions. Furthermore, we improve the determination of the form-factor parameters in ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{\ell }^{+}{\nu }_{\ell }$ decays, which provide stringent tests and calibration for lattice quantum chromodynamics calculations.

• Received 5 June 2023
• Accepted 17 July 2023

DOI:https://doi.org/10.1103/PhysRevD.108.L031105

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Published by the American Physical Society