Measurement of the branching fraction of the decay B+ → π+ π- l+ νl in fully reconstructed events at Belle

We present an analysis of the exclusive B+ -> pi(+) pi(-) l(+) nu(l) decay, where l represents an electron or a muon, with the assumption of charge-conjugation symmetry and lepton universality. The study exploits the full gamma (4S) data sample collected by the Belle detector, corresponding to 711 fb(-1) of integrated luminosity. Events are selected by fully reconstructing one B meson in hadronic decay modes, subsequently determining the properties of the other B meson. We extract the signal yields using a binned maximum-likelihood fit to the missing-mass squared distribution in bins of the invariant mass of the two pions or the momentum transfer squared. We measure a total branching fraction of B(B+ -> pi(+) pi(-) l(+) nu(l)) = [22.7(-1.6)(+1.9) (stat) +/- 3.5(syst) x 10(-5), where the uncertainties are statistical and systematic, respectively. This result is the first reported measurement of this decay.

Automated summary

The study analyzed the exclusive decay B+ -> pi(+) pi(-) l(+) nu(l) with Belle detector data, yielding a total branching fraction of B(B+ -> pi(+) pi(-) l(+) nu(l)) = 22.7 x 10^(-5), which is the first reported measurement of this decay process.