Observation of the B_c⁺→J/ψπ⁺π⁰ decay

The first observation of the B_c⁺→J/ψπ⁺π⁰ 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 π⁰ detection efficiency. The π⁺π⁰ mass spectrum is found to be consistent with the dominance of an intermediate ρ⁺ contribution in accordance with a model based on QCD factorisation.