Evidence for the semileptonic decays ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{\pm }{\pi }^{\mp }{e}^{+}{\nu }_e$

Using $4.5f{b}^{-1}$ of $e^{+}{e}^{-}$ collision data collected by the BESIII detector at center-of-mass energies between $4.600$ and $4.699GeV$, we search for the semileptonic decays ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}{\pi }^{-}{e}^{+}{\nu }_e$ and ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{-}{\pi }^{+}{e}^{+}{\nu }_e$ for the first time. Assuming their branching fractions are equal under isospin symmetry, evidence for ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{\pm }{\pi }^{\mp }{e}^{+}{\nu }_e$ is reported with a significance of $3.6\sigma$. The corresponding branching fraction is measured to be $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{\pm }{\pi }^{\mp }{e}^{+}{\nu }_e)=(7.7_{-{2.3}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}}}^{+2.5}\pm {1.3}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}})\times {10}^{-4}$, which is consistent with quark model predictions within two standard deviations.