Measurement of the Branching Fraction of the Decay ${\mathbf{B}}^{+}\to \ddot{\mathbf{I}}{€}^{+}\ddot{\mathbf{I}}{€}^{-}{\mathbf{\ell }}^{+}\hat{\mathbf{I}}{½}_{\mathbf{\ell }}$ in Fully Reconstructed Events at Belle

Abstract

We present an analysis of the exclusive $B^{+}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}{\ell }^{+}\hat{I}{½}_{\ell }$ decay, where $\ell$ represents an electron or a muon, with the assumption of charge-conjugation symmetry and lepton universality. The analysis uses the full $\hat{I}\yen (4S)$ data sample collected by the Belle detector, corresponding to 711 fb${}^{-1}$ of integrated luminosity. We select the events 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 $\mathcal{B}(B^{+}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}{\ell }^{+}\hat{I}{½}_{\ell })=[22.7_{-1.6}^{+1.9}(\mathrm{stat})\pm 3.5(\mathrm{syst})]\times 10^{-5}$, where the uncertainties are statistical and systematic, respectively. This result is the first reported measurement of this decay.

23 pages, 19 figures