Citation
CMS Collaboration, Chen, Z., Ecklund, K.M., et al.. "Observation of the ${\ensuremath{\chi}}_{b1}(3P)$ and ${\ensuremath{\chi}}_{b2}(3P)$ and Measurement of their Masses." Physical Review Letters, 121, no. 9 (2018) https://doi.org/10.1103/PhysRevLett.121.092002.
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.