Measurements of semileptonic and leptonic beauty meson decays at Belle II

TL;DR

This paper reports on three measurements of leptonic and semileptonic B meson decays at Belle II, including branching fractions, CKM matrix element determination, and tests of lepton flavor universality, using the full Run 1 dataset.

Contribution

It presents the first Belle II measurements of B meson decays with full Run 1 data, employing novel tagging methods for improved precision.

Findings

Measured B+ → τ ν branching fraction using hadronic tagging.

Determined |V_{cb}| from B → D ℓ ν decays with inclusive tagging.

Tested lepton flavor universality via R(D+) and R(D*+).

Abstract

Three recent measurements of leptonic and semileptonic decays of $B$ mesons are presented here. All results use the full Belle II Run 1 $e^+e^- \to \Upsilon(4S) \to B\bar{B}$ dataset of 365 fb$^{-1}$. We present one leptonic $B$ decay result: a measurement of the $B^+ \to \tau \nu$ branching fraction with a hadronic tagging method; and two semileptonic $B$ decay results: a determination of $|V_{cb}|$ using $B \to D \ell \nu$ decays with an inclusive tagging method and a test of lepton flavour universality with measurements of $\mathcal{R}\left(D^+\right)$ and $\mathcal{R}\left(D^{*+}\right)$ using semileptonic $B$ tagging.