Abstract
Using a data sample of s√= 13 TeV proton-proton collisions collected by the CMS experiment at the LHC in 2017 and 2018 with an integrated luminosity of 103 fb−1, the B0 → ψ(2S)K0S and B0S → ψ(2S)K0Sπ+π− decays are observed with significances exceeding 5 standard deviations. The resulting branching fraction ratios, measured for the first time, correspond to B(B0S → ψ(2S)K0S) / B(B0 → ψ(2S)K0S) = (3.33 ± 0.69 (stat) ± 0.11 (syst) ± 0.34 (fs/fd)) × 10−2 and B(B0 → ψ(2S)K0Sπ+π−) / B(B0 → ψ(2S)K0S) = 0.480 ± 0.013 (stat) ± 0.032 (syst), where the last uncertainty in the first ratio is related to the uncertainty in the ratio of production cross sections of B0s and B0 mesons, fs/fd.