Observation of the Bc^+ J/ ^+⁰ decay

The first observation of the Bc^+ J/ ^+ ⁰ decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9fb^-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 Bc^+ J/ ^+ channel is measured to be {B (Bc^+ J/ ^+⁰) } {B (Bc^+ J/ ^+) } = 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/ K^*+ and B^+ J/ K^+ decays, which are used to determine the ⁰ detection efficiency. The ^+⁰ mass spectrum is found to be consistent with the dominance of an intermediate ^+ contribution in accordance with a model based on QCD factorisation.