Searches for Λ0b and Ξ0b decays to K0Spπ− and K0SpK− final states with first observation of the Λ0b→K0Spπ− decay

Abstract

A search for previously unobserved decays of beauty baryons to the final states K0Spπ− and K0SpK− is reported. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fb−1 of pp collisions. The Λ0b→K¯¯¯¯¯0pπ−

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 fΛ0b/fd,

and from the branching fraction of the B 0 → K 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 Λ0b→K0SpK− decays, Ξ0b decays to both the K0Spπ− and K0SpK− final states, and the Λ0b→D−s(→K0SK−)p

decay, and upper limits on their branching fractions are reported.