First observation of the Λb⁰ → Λc⁺ Dₛ⁻ K⁺ K⁻ decay and search for pentaquarks in the Λc⁺ Ds⁻ system

The Λ0 b → Λþc D−s KþK− decay is observed for the first time using the data sample from proton-proton collisions recorded at a center-of-mass energy of 13 TeV with the LHCb detector, corresponding to an integrated luminosity of 6 fb−1. The ratio of branching fraction to that of Λ0 b → Λþc D−s decays is measured as 0.0141 0.0019 0.0012, where the first uncertainty is statistical and the second systematic. A search for hidden-charm pentaquarks with strangeness is performed in the Λþc D−s system. No evidence is found, and upper limits on the production ratio of Pc¯csð4338Þ0 and Pc¯csð4459Þ0 pentaquarks relative to the Λþc D−s final state are set at the 95% confidence level as 0.12 and 0.20, respectively.