Precise determination of the CKM matrix element $\left|V_{cb}\right|$ with ${\bar{B}}^0\to D^{\ast +}{\ell }^{-}{\bar{\nu }}_{\ell }$ decays with hadronic tagging at Belle

Abstract

The precise determination of the CKM matrix element $\left|V_{cb}\right|$ is important for carrying out tests of the flavour sector of the Standard Model. In this article we present a preliminary analysis of the ${\bar{B}}^0\to D^{\ast +}{\ell }^{-}{\bar{\nu }}_{\ell }$ decay mode and its charge conjugate, selected in events that contain a fully reconstructed $B$-meson, using 772 million $e^{+}{e}^{-}\to {\rm Y}(4S)\to B\bar{B}$ events recorded by the Belle detector at KEKB. Unfolded differential decay rates of four kinematic variables fully describing the ${\bar{B}}^0\to D^{\ast +}{\ell }^{-}{\bar{\nu }}_{\ell }$ decay in the $B$-meson rest frame are presented. We measure the total branching fraction $\mathcal{B}({\bar{B}}^0\to D^{\ast +}{\ell }^{-}{\bar{\nu }}_{\ell })=\left(4.95\pm 0.11\pm 0.22\right)\times 10^{-2}$, where the errors are statistical and systematic respectively. The value of $\left|V_{cb}\right|$ is determined to be $\left(37.4\pm 1.3\right)\times 10^{-3}$. Both results are in good agreement with current world averages.

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• $B$ decay anomalies from nonabelian local horizontal symmetry
• The fate of $V_1$ vector leptoquarks: the impact of future flavour data