Observation of the decay B\u305 0\u2192\u39bc+p\u305 \u3c00

In a sample of 467 million $B\overline B$ pairs collected with the BABAR detector at the PEP-II collider at SLAC we have observed the decay $\overline{B}^0\rightarrow\Lambda_c^+{\overline p} \pi^0$ and measured the branching fraction to be $(1.94\pm0.17 \pm 0.14 \pm 0.50)\times 10^{-4}$, where the uncertainties are statistical, systematic, and the uncertainty on the $\Lambda_c^+\rightarrow p {K^-} \pi^+$ branching fraction, respectively. We determine an upper limit of $1.5\times 10^{-6}$ at $90\%$ C.L. for the product branching fraction ${\cal B} (\overline{B}^0\rightarrow \Sigma_c^+(2455)\overline p)\times{\cal B} (\Lambda_c^+\rightarrow p K^- \pi^+)$. Furthermore, we observe an enhancement at the threshold of the invariant mass of the baryon-antibaryon pai