Publication
The decays Λb 0→Λc +D¯(∗)0K- and Λb 0→Λc +Ds ∗- are observed for the first time, in proton-proton collision data at s=13TeV, corresponding to an integrated luminosity of 5.4fb-1 collected with the LHCb detector. Their ratios of branching fractions with respect to the Λb 0→Λc +Ds - mode are measured to be (Formula presented.) where the first uncertainties are statistical, the second systematic, and the third, for the Λb 0→Λc +D¯(∗)0K- decays, are due to the uncertainties on the branching fractions of the Ds -→K-K+π- and D¯0→K+π- decay modes. The measured branching fractions probe factorization assumptions in effective theories and provide the normalization for future pentaquark searches in Λb 0→Λc +D¯(∗)0K- decay channels.