Measurement of the absolute branching fraction for $Λ^+_{c}\to Λe^+ν_e$

We report the first absolute measurement of the branching fraction of $Λ^+_{c}\rightarrow Λe^+ν_e$. This measurement is based on 567 pb$^{-1}$ of $e^+e^-$ annihilation data produced at $\sqrt{s}=4.599$ GeV, which is just above the $Λ^+_c\barΛ^-_c$ threshold. The data were collected with the BESIII detector at the BEPCII storage rings. The branching fraction is determined to be $\mathcal B({Λ^+_c\rightarrow Λe^+ν_e})=(3.63\pm0.38({\rm stat})\pm0.20({\rm syst}))\%$, representing a more than twofold improvement in precision upon previously published results. As the branching fraction for $Λ^+_{c}\rightarrow Λe^+ν_e$ is the benchmark for those of other $Λ^+_c$ semileptonic channels, our result provides a unique test of different theoretical models, which is the most stringent to date.

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