Searches for ${\Lambda }_b^0$ and ${\Xi }_b^0$ decays to $K_{\mathrm{S}}^{0}p{\pi }^{-}$ and $K_{\mathrm{S}}^{0}p{K}^{-}$ final states with first observation of the ${\Lambda }_b^0\to K_{\mathrm{S}}^{0}p{\pi }^{-}$ decay

Abstract

A search for previously unobserved decays of beauty baryons to the final states $K_{\mathrm{S}}^{0}p{\pi }^{-}$ and $K_{\mathrm{S}}^{0}p{K}^{-}$ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of $1.0$fb${}^{-1}$ of $pp$ collisions. The ${\Lambda }_b^0\to {\overline{K}}_{\mathrm{S}}^{0}p{\pi }^{-}$ decay is observed with a significance of $8.6\sigma$, with branching fraction \begin{eqnarray*} {\cal{B}}(Λ^0_{b} \rightarrow \overline{\kern -0.2em K}^0 p π^{-}) & = & \left(1.26 \pm 0.19 \pm 0.09 \pm 0.34 \pm 0.05 \right) \times 10^{-5} \,, \end{eqnarray*} where the uncertainties are statistical, systematic, from the ratio of fragmentation fractions $f_{\Lambda }/f_d$, and from the branching fraction of the $B^0\to K_{\mathrm{S}}^0{\pi }^{+}{\pi }^{-}$ normalisation channel, respectively. A first measurement is made of the $CP$ asymmetry, giving \begin{eqnarray*} A_{C/!P} (Λ^0_{b} \rightarrow \overline{\kern -0.2em K}^0 p π^{-}) & = & 0.22 \pm 0.13\mathrm{\,(stat)} \pm 0.03\mathrm{\,(syst)} \, . \end{eqnarray*} No significant signals are seen for ${\Lambda }_b^0\to K_{\mathrm{S}}^{0}p{K}^{-}$ decays, ${\Xi }_b^0$ decays to both the $K_{\mathrm{S}}^{0}p{\pi }^{-}$ and $K_{\mathrm{S}}^{0}p{K}^{-}$ final states, and the ${\Lambda }_b^0\to D_s^{-}(\to K_{\mathrm{S}}^0{K}^{-})p$ decay, and upper limits on their branching fractions are reported.

27 pages, 4 figures

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