Measurement of the $\ddot{I}„$ lepton polarization in the decay $\bar{B}\to D^{\ast }\ddot{I}{„}^{-}\bar{\hat{I}}{½}_{\ddot{I}}„$

Abstract

We report the first measurement of the $\ddot{I}„$ lepton polarization in the decay $\bar{B}\to D^{\ast }\ddot{I}{„}^{-}\bar{\hat{I}}{½}_{\ddot{I}}„$ as well as a new measurement of the ratio of the branching fractions $R(D^{\ast })=\mathcal{B}(\bar{B}\to D^{\ast }\ddot{I}{„}^{-}\bar{\hat{I}}{½}_{\ddot{I}}„)/\mathcal{B}(\bar{B}\to D^{\ast }{\ell }^{-}\bar{\hat{I}}{½}_{\ell })$, where ${\ell }^{-}$ denotes an electron or a muon, with the decays $\ddot{I}{„}^{-}\to \ddot{I}{€}^{-}\hat{I}{½}_{\ddot{I}}„$ and $\ddot{I}{„}^{-}\to \ddot{I}{}^{-}\hat{I}{½}_{\ddot{I}}„$. We use the full data sample of $772\times 10^6$ $B\bar{B}$ pairs accumulated with the Belle detector at the KEKB electron-positron collider. Our preliminary results, $R(D^{\ast })=0.276\pm 0.034{(stat.)}_{-0.026}^{+0.029}(syst.)$ and $P_{\ddot{I}}„=-0.44\pm 0.47{(stat.)}_{-0.17}^{+0.20}(syst.)$, are consistent with the theoretical predictions of the Standard Model within $0.6$ standard deviation.

31 pages, 6 figures, ICHEP 2016