Search for baryons in the radiative penguin decay $\overrightarrow{b}s\gamma$

We have searched for the baryon-containing radiative penguin decays $B^{-}\to \Lambda \overline{p}\gamma$ and $B^{-}\to {\Sigma }^0\overline{p}\gamma ,$ using a sample of $9.7\times {10}^6$ $B\overline{B}$ events collected at the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ with the CLEO detector. We find no evidence for either, and set 90% confidence level upper limits of $\mathcal{B}{(B}^{-}\to \Lambda \overline{p}\gamma )+0.3\mathrm{}\mathcal{B}{(B}^{-}\to {\Sigma }^0\overline{p}\gamma ){]}_{E_{\gamma }>2.0\mathrm{}\hspace{0.5em}\mathrm{GeV}}<3.3\mathrm{}\times {10}^{-6},$ $[\mathcal{B}{(B}^{-}\to {\Sigma }^0\overline{p}\gamma )+0.4\mathrm{}\mathcal{B}{(B}^{-}\to \Lambda \overline{p}\gamma ){]}_{E_{\gamma }>2.0\mathrm{}\hspace{0.5em}\mathrm{GeV}}<6.4\mathrm{}\times {10}^{-6}.$ From the latter, we estimate $\mathcal{B}(\overrightarrow{B}{X}_s\gamma {,X}_s\hspace{0.5em}\mathrm{containing}\mathrm{}\mathrm{baryons}{)}_{E_{\gamma }>2.0\mathrm{}\hspace{0.5em}\mathrm{GeV}}<3.8\mathrm{}\times {10}^{-5}.$ This limit implies upper limits on corrections to CLEO’s recent measurement of branching fraction, mean photon energy, and variance in photon energy from $\overrightarrow{b}s\gamma$ that are less than half the combined statistical and systematic errors quoted on these quantities.