Observation of the B⁺ → Jψη′K⁺ decay

The B⁺ → Jψη′K⁺ decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb⁻¹. The branching fraction of this decay is measured relative to the known branching fraction of the B⁺ → ψ(2S)K⁺ decay and found to be B(B⁺→Jψη′K⁺)B(B⁺→ψ(2S)K⁺)=(4.91±0.47±0.29±0.07)×10⁻², where the first uncertainty is statistical, the second is systematic and the third is related to external branching fractions. A first look at the J/ψη′ mass distribution is performed and no signal of intermediate resonances is observed. [Figure not available: see fulltext.]