# Test of lepton-flavor universality in ${B\to K^\ast\ell^+\ell^-}$ decays at Belle

## TL;DR

This paper reports measurements of lepton-flavor universality in B meson decays to K* and dileptons, including the first measurement of the charged B decay ratio, using Belle data, with results consistent with the Standard Model.

## Contribution

First measurement of the lepton-flavor universality ratio $R_{K^*}$ for charged B mesons, along with absolute branching fractions in various $q^2$ bins, using a large Belle dataset.

## Key findings

- Results are consistent with Standard Model predictions.
- First measurement of $R_{K^{*+}}$ for charged B decays.
- Provides detailed branching fractions across $q^2$ bins.

## Abstract

We present a measurement of $R_{K^{\ast}}$, the branching fraction ratio ${{\cal B}(B\to K^\ast \mu^+ \mu^-)}$/ ${{\cal B}(B\to K^\ast e^+ e^-)}$, for both charged and neutral $B$ mesons. The ratio for the charged case, $R_{K{^{\ast +}}}$, is the first measurement ever performed. In addition, we report absolute branching fractions for the individual modes in bins of the squared dilepton invariant mass, $q^2$. The analysis is based on a data sample of $711~\mathrm{fb}^{-1}$, containing $772\times 10^{6}$ $B\bar B$ events, recorded at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The obtained results are consistent with Standard Model expectations.