Search for exclusive rare baryonic decays of B mesons

We report the results of a search for the rare baryonic decay modes $B^0\to \Lambda \overline{\Lambda },$ $B^{+}\to \overline{\Lambda }p,$ $B^0\to \overline{\Lambda }p{\pi }^{-},$ and $B^0\to p\overline{p}$ (and their charge conjugate states) using $5.8\times {10}^6\hspace{0.5em}B\overline{B}$ pairs collected with the CLEO detector. We see no statistically significant signals in any of these modes and set 90% confidence level upper limits on their branching fractions, $\mathcal{B}{(B}^0\to \Lambda \overline{\Lambda })<\mathrm{}3.9\mathrm{}\times {10}^{-6},$ $\mathcal{B}{(B}^{+}\to \overline{\Lambda }p)<\mathrm{}2.6\mathrm{}\times {10}^{-6},$ $\mathcal{B}{(B}^0\to \overline{\Lambda }p{\pi }^{-})<\mathrm{}1.3\mathrm{}\times {10}^{-5},$ and $\mathcal{B}{(B}^0\to p\overline{p})<\mathrm{}7.0\mathrm{}\times {10}^{-6}.$