Measurement of the branching ratio of ${\bar{B}}^0\to D^{\ast +}\ddot{I}{„}^{-}\bar{\hat{I}}{½}_{\ddot{I}}„$ relative to ${\bar{B}}^0\to D^{\ast +}{\ell }^{-}\bar{\hat{I}}{½}_{\ell }$ decays with a semileptonic tagging method

Abstract

We report a measurement of ratio $\mathcal{R}(D^{\ast })=\mathcal{B}({\bar{B}}^0\to D^{\ast +}\ddot{I}{„}^{-}\bar{\hat{I}}{½}_{\ddot{I}}„)/\mathcal{B}({\bar{B}}^0\to D^{\ast +}{\ell }^{-}\bar{\hat{I}}{½}_{\ell })$, where $\ell$ denotes an electron or a muon. The results are based on a data sample containing $772\times 10^6$ $B\bar{B}$ pairs recorded at the $\hat{I}\yen (4S)$ resonance with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider. We select a sample of $B^0{\bar{B}}^0$ pairs by reconstructing both $B$ mesons in semileptonic decays to $D^{\ast \mp }{\ell }^{\pm }$. We measure $\mathcal{R}(D^{\ast })=0.302\pm 0.030(\mathrm{stat})\pm 0.011(\mathrm{syst})$, which is within $1.6\ddot{I}ƒ$ of the Standard Model theoretical expectation, where $\ddot{I}ƒ$ is the standard deviation including systematic uncertainties.

12pages, 13 figures, Moriond EW 2016