Observation of the χb1 (3P) and χb2 (3P) and measurement of their masses

The χ_(b1)(3P) and χ_(b2)(3P) states are observed through their Υ(3S)γ decays, using an event sample of proton-proton collisions collected by the CMS experiment at the CERN LHC. The data were collected at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 80.0  fb^(-1). The Υ(3S) mesons are identified through their dimuon decay channel, while the low-energy photons are detected after converting to e^+e^− pairs in the silicon tracker, leading to a χ_b(3P) mass resolution of 2.2 MeV. This is the first time that the J = 1 and 2 states are well resolved and their masses individually measured: 10513.42 ± 0.41(stat) ± 0.18(syst)  MeV and 10524.02 ± 0.57(stat) ± 0.18(syst)  MeV; they are determined with respect to the world-average value of the Υ(3S) mass, which has an uncertainty of 0.5 MeV. The mass splitting is measured to be 10.60 ± 0.64(stat) ± 0.17(syst)  MeV.