Observation of the χb1 (3P) and χb2 (3P) and Measurement of their Masses

Abstract

The χb1(3P) and χb2(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 χb(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.