Michele Mantovano

21 July 2024

Abstract: The Belle and Belle II experiments have collected a $1.1$\,ab$^{-1}$ sample of $e^{+}e^{-} \rightarrow B\bar B$ collisions at the $\Upsilon(4S)$ resonance. These data, with low particle multiplicity, constrained initial state kinematics and excellent lepton identification, are an ideal environment to study lepton-flavour universality in semileptonic decays of the $B$ meson. We present measurements of branching-fraction ratios that test the universality of $\tau$ and light leptons, using both exclusive and inclusive $B$ semileptonic decays. We also report measurements of angular observables that probe universality between electrons and muons.

Keyword(s): lepton-flavour universality ; semileptonic B decays ; angular asymmetries