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Measurement of the branching fraction of the decay B+ -> pi(+) pi(-) l(+) nu(l) in fully reconstructed events at Belle

Publication at Faculty of Mathematics and Physics |
2021

Abstract

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.