Observation of the decay ${\overline{B}}^0\to D_s^{+}\Lambda \overline{p}$

We report the first observation of the decay ${\overline{B}}^0\to D_s^{+}\Lambda \overline{p}$ with a statistical significance of $6.6\sigma$. We measure $\mathcal{B}({\overline{B}}^0\to D_s^{+}\Lambda \overline{p})=(2.9\pm 0.7\pm 0.5\pm 0.4)\times {10}^{-5}$, where the first error is statistical, the second is systematic, and the third error comes from the uncertainty in $\mathcal{B}(D_s^{+}\to \varphi {\pi }^{+})$. The data used for this analysis was accumulated at the ${\rm Y}(4S)$ resonance, using the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The integrated luminosity of the data sample is $414{\mathrm{fb}}^{-1}$, corresponding to $449\times {10}^6$ $B\overline{B}$ pairs.

Figure 1

(a) The $M_{\mathrm{bc}}$ and (b) $\Delta M$ distributions for the ${\overline{B}}^0\to D_s^{+}\Lambda \overline{p}$ candidates (triangles with error bars). The hatched histograms show the $D_s^{+}$ mass sidebands normalized to the signal region. The overlaid curves are fit results (see text for details). (c) The $\overline{p}\Lambda$ and (d) $D_s^{+}\Lambda$ invariant mass distributions in the $B$-signal region (open histogram) and in the $B$-sideband (hatched histogram).

Figure 2

Cross-checks of the signal. (a) and (b) are the $M_{\mathrm{bc}}$ and $\Delta M$ distributions for the on-resonance data with the inverted requirement on the normalized Fox-Wolfram moment $R_2$ (see text for details). (c) and (d) are the $M_{\mathrm{bc}}$ and $\Delta M$ distributions for the continuum data. (e) and (f) are the $M_{\mathrm{bc}}$ and $\Delta M$ distributions for the primary vertex protons with inverted identification. No peaking structure in the signal region is present in any of the cross-check analyses.