Study of $$\upchi _{{\mathrm {b}}}$$ χ b meson production in $$\mathrm {p} $$ p $$\mathrm {p} $$ p collisions at $$\sqrt{s}=7$$ s = 7 and $$8{\mathrm {\,TeV}} $$ 8 TeV and observation of the decay $$\upchi _{{\mathrm {b}}}\mathrm {(3P)} \rightarrow \Upsilon \mathrm {(3S)} {\upgamma } $$ χ b ( 3 P ) → Υ ( 3 S ) γ

A study of $$\upchi _{{\mathrm {b}}}$$ meson production at LHCb is performed on proton–proton collision data, corresponding to 3.0 $$\text { fb}^{-1}$$ of integrated luminosity collected at centre-of-mass energies $$\sqrt{s}$$ = 7 and 8 $$\mathrm {\,TeV}$$ . The fraction of $$\Upsilon \mathrm {(nS)}$$ mesons originating from $$\upchi _{{\mathrm {b}}}$$ 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 $$\upchi _{{\mathrm {b}}}\mathrm {(3P)}$$ meson to $$\Upsilon \mathrm {(3S)}$$ is observed for the first time. The $$\upchi _{{\mathrm {b}} 1}\mathrm {(3P)}$$ mass is determined to be $$\begin{aligned} m_{\upchi _{{\mathrm {b}} 1}\mathrm {(3P)}} = 10\,511.3 \pm 1.7 \pm 2.5{\mathrm {\,MeV}/c^2}, \end{aligned}$$ where the first uncertainty is statistical and the second is systematic.