Observation of the B⁺_c → J/ψπ⁺π⁰ decay

The frst 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
^BB⁺_c →J/ψπ⁺π^0
BB⁺_c →J/ψπ⁺
= 2.80 ± 0.15 ± 0.11 ± 0.16 ,
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.