First observation of the Λ_b⁰ → Λ_c⁺ D_s^-K ⁺K^- decay and search for pentaquarks in the Λ_c⁺D_s^- system

The Λ⁰_b → Λ_c⁺D⁻_sK⁺K⁻ 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 → Λ_c⁺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 Λ_c⁺D⁻_s system. No evidence is found, and upper limits on the production ratio of P_cc-s(4338)⁰ and P_cc-s(4459)⁰ pentaquarks relative to the Λ_c⁺D^-_s final state are set at the 95% confidence level as 0.12 and 0.20, respectively