Observation of the Baryonic Decayb¯0→λc+p¯

We report the observation of the baryonic decay ${\overline{B}}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\overline{p}{K}^{\ensuremath{-}}{K}^{+}$ using a data sample of $471\ifmmode\times\else\texttimes\fi{}1{0}^{6}$ $B\overline{B}$ pairs produced in ${e}^{+}{e}^{\ensuremath{-}}$ annihilations at $\sqrt{s}=10.58\text{ }\text{ }\mathrm{GeV}$. This data sample was recorded with the BABAR detector at the PEP-II storage ring at SLAC. We find $\mathcal{B}({\overline{B}}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\overline{p}{K}^{\ensuremath{-}}{K}^{+})=(2.5\ifmmode\pm\else\textpm\fi{}0.{4}_{(\text{stat})}\ifmmode\pm\else\textpm\fi{}0.{2}_{(\text{syst})}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0ex}{0ex}}0.{6}_{\mathcal{B}({\mathrm{\ensuremath{\Lambda}}}_{c}^{+})})\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}5}$, where the uncertainties are statistical, systematic, and due to the uncertainty of the ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}p{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ branching fraction, respectively. The result has a significance corresponding to 5.0 standard deviations, including all uncertainties. For the resonant decay ${\overline{B}}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\overline{p}\ensuremath{\phi}$, we determine the upper limit $\mathcal{B}({\overline{B}}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\overline{p}\ensuremath{\phi})<1.2\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}5}$ at 90% confidence level.