Study of $chi_{b}$ meson production in pp collisions at $sqrt{s}=7$ and 8TeV and observation of the decay $chi_{b}rightarrow Upsilon(3S) gamma$

A study of $chi_{b}$ meson production at LHCb is performed on proton-proton collision data, corresponding to 3.0fb$^{-1}$ of integrated luminosity collected at centre-of-mass energies $sqrt{s}=7$ and 8TeV. The fraction of $Upsilon(nS)$ mesons originating from $chi_{b}$ decays is measured as a function of the $Upsilon$ transverse momentum in the rapidity range $2.0 < y^{Upsilon} < 4.5$. The radiative transition of the $chi_{b}(3P)$ meson to $Upsilon(3S)$ is observed for the first time. The $chi_{b1}(3P)$ mass is determined to be $$m(chi_{b1}(3P)) = 10,511.3 pm 1.7 pm 2.5 MeV/c^2,$$ where the first uncertainty is statistical and the second is systematic.