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.]