Study of η–η′ mixing in B-meson decay with the LHCb detector

The first ever observation of the decay process B0 → J/ψη′ is described. The branching ratios were measured for the decay processes B(s) → J/ψη(′), and the η–η′ mixing angles were determined on this basis. The first indication of the occurrence of the decay process Bs → ψ(2S)η′ is presented. The respective analysis was performed on the basis of data accumulated with the LHCb detector in proton–proton collisions at the c.m. collision energies of 7 and 8 TeV and the integrated luminosity of 3 fb−1.