Observation of the Λ _b ⁰→Λ _c ⁺K ⁺K ⁻π ⁻ decay

The Λ _b ⁰→Λ _c ⁺K ⁺K ⁻π ⁻ decay is observed for the first time using a data sample of proton-proton collisions at centre-of-mass energies of s=7 and 8TeV collected by the LHCb detector, corresponding to an integrated luminosity of 3fb ⁻¹. The ratio of branching fractions between the Λ _b ⁰→Λ _c ⁺K ⁺K ⁻π ⁻ and the Λ _b ⁰→Λ _c ⁺D _s ⁻ decays is measured to be [Formula presented] where the first uncertainty is statistical, the second systematic and the third is due to the knowledge of the D _s ⁻→K ⁺K ⁻π ⁻ branching fraction. No structure on the invariant mass distribution of the Λ _c ⁺K ⁺ system is found, consistent with no open-charm pentaquark signature.