Observation of the ${\chi }_{b1}$(3P) and ${\chi }_{b2}$(3P) and measurement of their masses

Abstract

The ${\chi }_{b1}$(3P) and ${\chi }_{b2}$(3P) states are observed through their ${\rm Y}$(3S) $\gamma$ 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 ${\rm Y}$(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 ${\chi }_{\mathrm{b}}$(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 $\pm$ 0.41 (stat) $\pm$ 0.18 (syst) MeV and 10524.02 $\pm$ 0.57 (stat) $\pm$ 0.18 (syst) MeV; they are determined with respect to the world-average value of the ${\rm Y}$(3S) mass, which has an uncertainty of 0.5 MeV. The mass splitting is measured to be 10.60 $\pm$ 0.64 (stat) $\pm$ 0.17 (syst) MeV.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/BPH-17-008 (CMS Public Pages)