Observation of the Decay ${\overline{B}}^0\to {\Lambda }_c^{+}\overline{p}$

We report the measurement of the charmed baryonic decay ${\overline{B}}^0\to {\Lambda }_c^{+}\overline{p}$ with a branching fraction of $({2.19}_{-0.49}^{+0.56}\pm 0.32\pm 0.57)\times {10}^{-5}$ and a statistical significance of $5.8\sigma$. The errors are statistical, systematic, and the error of the ${\Lambda }_c^{+}\to p{K}^{-}{\pi }^{+}$ decay branching fraction. This is the first observation of a two-body baryonic $B$ decay. The analysis is based on $78.2{\mathrm{f}\mathrm{b}}^{-1}$ of data accumulated at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric $e^{+}{e}^{-}$ collider.

Figure 1

Candidate ${\overline{B}}^0\to {\Lambda }_c^{+}\overline{p}$ events: (a) scatter plot of $\Delta E$ versus $M_{\mathrm{b}\mathrm{c}}$, (b) $\Delta E$ distribution for $M_{\mathrm{b}\mathrm{c}}>5.270\mathrm{G}\mathrm{e}\mathrm{V}/c^2$, and (c) $M_{\mathrm{b}\mathrm{c}}$ distribution for $|\Delta E|<0.030\mathrm{G}\mathrm{e}\mathrm{V}$. The curves indicate the result of a two-dimensional fit.

Figure 2

Invariant mass $M(p{K}^{-}{\pi }^{+})$ distribution for ${\overline{B}}^0\to {\Lambda }_c^{+}\overline{p}$ candidates in the $B$ signal region.