Observation of the B _c ⁺→J/ψπ ⁺π ⁰ decay

The first observation of the B _c ⁺→J/ψπ ⁺π ⁰ decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9 fb ⁻¹, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the B _c ⁺→J/ψπ ⁺ channel is measured to be (Formula presented.) where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for B ⁺ → J/ψK ^*+ and B _c ⁺→J/ψπ ⁺ decays, which are used to determine the π ⁰ detection efficiency. The π ⁺π ⁰ mass spectrum is found to be consistent with the dominance of an intermediate ρ ⁺ contribution in accordance with a model based on QCD factorisation.