Search for the weak radiative decay ${\Lambda }_{c}^{+}\to {\Sigma }^{+}\gamma $ at BESIII

The Cabibbo-allowed weak radiative decay ${\Lambda }_{c}^{+}\to {\Sigma }^{+}\gamma $ has been searched for in a sample of ${\Lambda }_{c}^{+}{\overline{\Lambda }}_{c}^{-}$ pairs produced in ${e}^{+}{e}^{-}$ annihilations, corresponding to an integrated luminosity of $4.5\text{}\text{}{\mathrm{fb}}^{-1}$ collected with the BESIII detector at center-of-mass energies between 4.60 and 4.70 GeV. No excess of signal above background is observed, and we set an upper limit on the branching fraction of this decay to be $B\left({\Lambda }_{c}^{+}\to {\Sigma }^{+}\gamma \right)<4.4×{10}^{-4}$ at a confidence level of 90%, which is in agreement with Standard Model expectations.