First search for the weak radiative decays ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}\gamma$ and ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^0\gamma$

We present the first search for the weak radiative decays ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}\gamma$ and ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^0\gamma$ using a data sample of 980~fb${}^{-1}$ collected by the Belle detector operating at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. There are no evident ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}\gamma$ or ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^0\gamma$ signals. Taking the decays ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$ and ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+}$ as normalization channels, the upper limits at 90% credibility level on the ratios of branching fractions $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}\gamma )\mathrm{/}\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+})<4.0\times {10}^{-3}$ and $\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^0\gamma )\mathrm{/}\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+})<1.2\times {10}^{-2}$ are determined. We obtain the upper limits at 90% credibility level on the absolute branching fractions $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}\gamma )<2.6\times {10}^{-4}$ and $\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^0\gamma )<1.8\times {10}^{-4}$.