Observation of the semileptonic decay B⁺→ pp¯ μ⁺ν_μ

The Cabibbo-suppressed semileptonic decay B⁺→ pp¯ μ⁺ν_μ is observed for the first time using a sample of pp collisions corresponding to an integrated luminosity of 1.0, 2.0 and 1.7 fb⁻¹ at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The differential branching fraction is measured as a function of the pp¯ invariant mass using the decay mode B⁺→ J/ψK⁺ for normalisation. The total branching fraction is measured to be ℬ(B+→pp¯μ+νμ)=(5.27−0.24+0.23±0.21±0.15)×10−6, where the first uncertainty is statistical, the second systematic and the third is from the uncertainty on the branching fraction of the normalisation channel. [Figure not available: see fulltext.]