Observation of the Ξ−b→J/ψΛK−decay

Abstract

The observation of the decay Ξ−b→J/ψΛK−is reported, using a data sample corresponding to an integrated luminosity of 3 fb−1, collected by the LHCb detector in ppcollisions at centre-of-mass energies of 7and 8 TeV. The production rate of Ξ−bbaryons detected in the decay Ξ−b→J/ψΛK−is measured relative to that of Λ0bbaryons using the decay Λ0b→J/ψΛ. Integrated over the b-baryon transverse momentum pT<25 GeV/cand rapidity 2.0 <y <4.5, the measured ratio is fΞ − b fΛ0 b B(Ξ − b → J/ψΛK− ) B(Λ0 b → J/ψΛ) = (4.19±0.29 (stat)± 0.15 (syst))×10−2, where fΞ−band fΛ0bare the fragmentation fractions of b →Ξ−band b →Λ0btransitions, and Brepresents the branching fraction of the corresponding b-baryon decay. The mass difference between Ξ−band Λ0bbaryons is measured to be M(Ξ − b )− M(Λ0 b ) = 177.08±0.47 (stat)± 0.16 (syst)MeV/c2.