Measurement of the ${\chi }_b(3P)$ mass and of the relative rate of ${\chi }_{b1}(1P)$ and ${\chi }_{b2}(1P)$ production

The production of ${\chi }_b$ mesons in proton-proton collisions is studied using a data sample collected by the LHCb detector, at centre-of-mass energies of $\sqrt{s}=7$ and $8$ TeV and corresponding to an integrated luminosity of 3.0 fb${}^{-1}$. The ${\chi }_b$ mesons are identified through their decays to $\mathrm{{\rm Y}}(1S)\gamma$ and $\mathrm{{\rm Y}}(2S)\gamma$ using photons that converted to $e^{+}{e}^{-}$ pairs in the detector. The relative prompt production rate of ${\chi }_{b1}(1P)$ and ${\chi }_{b2}(1P)$ mesons is measured as a function of the $\mathrm{{\rm Y}}(1S)$ transverse momentum in the ${\chi }_b$ rapidity range $2.0<y<4.5$. A precise measurement of the ${\chi }_b(3P)$ mass is also performed. Assuming a mass splitting between the ${\chi }_{b1}(3P)$ and the ${\chi }_{b2}(3P)$ states of 10.5 MeV/$c^2$, the measured mass of the ${\chi }_{b1}(3P)$ meson is $m({\chi }_{b1}(3P))=10515.7_{-3.9}^{+2.2}(stat{)}_{-2.1}^{+1.5}(syst)MeV\mathrm{/}{c}^2\mathrm{.}$