Observation of the Lambda0_b -> J/psi Xi- K+ decay

sing proton–proton collision data correspond ing to an integrated luminosity of 140 fb−1 collected by the CMS experiment at √s = 13 TeV, the 0 b → J/ψ −K+decay is observed for the first time, with a statistical sig nificance exceeding 5 standard deviations. The relative branching fraction, with respect to the 0 b → ψ(2S) decay, is measured to be B( 0 b → J/ψ −K+)/B( 0 b →ψ(2S) ) = [3.38 ± 1.02 ± 0.61 ± 0.03]%, where the first uncertainty is statistical, the second is systematic, and the third is related to the uncertainties in B(ψ(2S) →J/ψπ+π−) and B( − → π−)