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

TL;DR

This paper presents a precise measurement of the CKM matrix element |V_{cb}| using semileptonic B meson decays at Belle, including unfolded differential decay rates and a total branching fraction, confirming consistency with world averages.

Contribution

The study provides a preliminary, high-precision determination of |V_{cb}| from B to D* l nu decays with hadronic tagging at Belle, utilizing a large dataset and unfolding techniques.

Findings

Measured total branching fraction: (4.95 ± 0.11 ± 0.22) × 10^{-2}

Determined |V_{cb}|: (37.4 ± 1.3) × 10^{-3}

Results agree with current world averages.

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 $\bar B^0 \to D^{*\,+} \, \ell^- \, \bar \nu_\ell$ decay mode and its charge conjugate, selected in events that contain a fully reconstructed $B$-meson, using 772 million $e^+ \, e^- \to \Upsilon(4S) \to B \bar B$ events recorded by the Belle detector at KEKB. Unfolded differential decay rates of four kinematic variables fully describing the $\bar B^0 \to D^{*\,+} \, \ell^- \, \bar \nu_\ell$ decay in the $B$-meson rest frame are presented. We measure the total branching fraction $\mathcal{B}( \bar B^0 \to D^{*\,+} \, \ell^- \, \bar \nu_\ell ) = \left(4.95 \pm 0.11 \pm 0.22 \right) \times 10^{-2}$, 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.