Measurements of lepton-flavour universality in semileptonic B decays at Belle and Belle II

Abstract

The Belle and Belle II experiments have collected a 1.1 ab−1 sample of e+e− BB¯ collisions at the ϒ(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 τ 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.