Tests of light-lepton universality in angular asymmetries of $B^0 \to D^{*-} \ell \nu$ decays

TL;DR

This study tests light-lepton universality in $B^0$ decays by analyzing angular asymmetries, finding no significant deviations from the Standard Model in a large dataset from Belle II.

Contribution

First comprehensive analysis of angular asymmetries in $B^0$ decays to test lepton universality with no observed deviations.

Findings

No significant deviation from Standard Model expectations.

Measured angular asymmetries are consistent across lepton flavors.

Results constrain new physics models affecting lepton universality.

Abstract

We present the first comprehensive tests of light-lepton universality in the angular distributions of semileptonic $B^0$-meson decays to charged spin-1 charmed mesons. We measure five angular-asymmetry observables as functions of the decay recoil that are sensitive to lepton-universality-violating contributions. We use events where one neutral $B$ is fully reconstructed in $\Upsilon\left(4S\right)\to{}B \overline{B}$ decays in data corresponding to $189~\mathrm{fb}^{-1}$ integrated luminosity from electron-positron collisions collected with the Belle II detector. We find no significant deviation from the standard model expectations.