Search for exclusive rare baryonic decays of<b><i>B</i></b>mesons

We report the results of a search for the rare baryonic decay modes ${B}^{0}\ensuremath{\rightarrow}\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}},$ ${B}^{+}\ensuremath{\rightarrow}\overline{\ensuremath{\Lambda}}p,$ ${B}^{0}\ensuremath{\rightarrow}\overline{\ensuremath{\Lambda}}p{\ensuremath{\pi}}^{\ensuremath{-}},$ and ${B}^{0}\ensuremath{\rightarrow}p\overline{p}$ (and their charge conjugate states) using $5.8\ifmmode\times\else\texttimes\fi{}{10}^{6} B\overline{B}$ 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, $\mathcal{B}{(B}^{0}\ensuremath{\rightarrow}\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}})&lt;3.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6},$ $\mathcal{B}{(B}^{+}\ensuremath{\rightarrow}\overline{\ensuremath{\Lambda}}p)&lt;2.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6},$ $\mathcal{B}{(B}^{0}\ensuremath{\rightarrow}\overline{\ensuremath{\Lambda}}p{\ensuremath{\pi}}^{\ensuremath{-}})&lt;1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5},$ and $\mathcal{B}{(B}^{0}\ensuremath{\rightarrow}p\overline{p})&lt;7.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}.$