Using $29.1{\mathrm{fb}}^{-1}$ of data accumulated at the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ with the Belle detector at KEKB, we have studied the decay modes $B^0\to {\Lambda }_c^{+}\overline{p}{\pi }^{+}{\pi }^{-},$ $B^{-}\to {\Lambda }_c^{+}\overline{p}{\pi }^{-},$ and $B^0\to {\Lambda }_c^{+}\overline{p}.$ We report branching fractions of exclusive B decays to charmed baryons with four-, three- and two-body final states, including intermediate ${\Sigma }_c^{++}$ and ${\Sigma }_c^0$ states. We observed $B^0\to {\Sigma }_c{\mathrm{}\left(2455\right)\mathrm{}}^{++}\overline{p}{\pi }^{-}$ for the first time with a branching fraction of ${(2.38\mathrm{}}_{-0.55}^{+0.63\mathrm{}}\pm 0.41\pm 0.62)\times {10}^{-4}$ and observed evidence for the two-body decay $B^{-}\to {\Sigma }_c{\mathrm{}\left(2455\right)\mathrm{}}^0\overline{p}$ with a branching fraction of ${(0.45\mathrm{}}_{-0.19}^{+0.26\mathrm{}}\pm 0.07\pm 0.12)\times {10}^{-4}.$ We also set improved upper limits for the two-body decays $B^0\to {\Lambda }_c^{+}\overline{p}$ and $B^{-}\to {\Sigma }_c{\mathrm{}\left(2520\right)\mathrm{}}^0\overline{p}.$

• Received 25 August 2002

DOI:https://doi.org/10.1103/PhysRevD.66.091102