Searches for \( \Lambda_b^0 \) and \( \Xi_b^0 \) decays to \( K_{\mathrm{S}}^0p{\pi^{-}} \) and \( K_{\mathrm{S}}^0p{K^{-}} \) final states with first observation of the \( \Lambda_b^0\to K_{\mathrm{S}}^0p{\pi^{-}} \) decay

Abstract

A search for previously unobserved decays of beauty baryons to the final states \( K_{\mathrm{S}}^0p{\pi^{-}} \) and \( K_{\mathrm{S}}^0p{K^{-}} \) is reported. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fb−1 of pp collisions. The \( \Lambda_b^0\to {{\overline{K}}^0}p{\pi^{-}} \) decay is observed with a significance of 8.6 σ, with branching fraction

$ \mathcal{B}\left( {\Lambda_b^0\to {{\overline{K}}^0}p{\pi^{-}}} \right)=\left( {1.26\pm 0.19\pm 0.09\pm 0.34\pm 0.05} \right)\times {10^{-5 }}, $

where the uncertainties are statistical, systematic, from the ratio of fragmentation fractions \( {{{{f_{{\Lambda_b^0}}}}} \left/ {{{f_d}}} \right.}, \) and from the branching fraction of the B 0K 0 π + π normalisation channel, respectively. A first measurement is made of the CP asymmetry, giving

$ {A_{CP }}\left( {\Lambda_b^0\to {{\overline{K}}^0}p{\pi^{-}}} \right)=0.22\pm 0.13\left( {\mathrm{stat}} \right)\pm 0.03\left( {\mathrm{syst}} \right). $

No significant signals are seen for \( \Lambda_b^0\to K_{\mathrm{S}}^0p{K^{-}} \) decays, \( \Xi_b^0 \) decays to both the \( K_{\mathrm{S}}^0p{\pi^{-}} \) and \( K_{\mathrm{S}}^0p{K^{-}} \) final states, and the \( \Lambda_b^0\to D_s^{-}\left( {\to K_{\mathrm{S}}^0{K^{-}}} \right)p \) decay, and upper limits on their branching fractions are reported.

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