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 K0 S pπ− and K0 S pK− is reported. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fb−1 of pp collisions. The Λ 0 b → K0pπ− decay is observed with a significance of 8.6 σ, with branching fraction B(Λ 0 b → K0 pπ−) = (1.26 ± 0.19 ± 0.09 ± 0.34 ± 0.05) × 10−5 , where the uncertainties are statistical, systematic, from the ratio of fragmentation fractions fΛ0 b /fd, and from the branching fraction of the B0→ K0π +π − normalisation channel, respectively. A first measurement is made of the CP asymmetry, giving ACP (Λ 0 b → K0 pπ−) = 0.22 ± 0.13 (stat) ± 0.03 (syst). No significant signals are seen for Λ 0 b → K0 S pK− decays, Ξ0 b decays to both the K0 S pπ− and K0 S pK− final states, and the Λ 0 b → D− s (→ K0 SK−)p decay, and upper limits on their branching fractions are reported.