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 BB+c →J/ψπ+π0BB+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.