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We present recent tests of lepton universality as crucial probes of the Standard Model in semileptonic B-meson decays at Belle II. All presented analyses use a data sample collected at the (4S) resonance by the Belle II experiment corresponding to an integrated luminosity of 189\, fb^-1. We report three analyses that probe light-lepton universality: The first measurement of a complete set of five angular asymmetries using B⁰ D^*+ ^- _ decays, followed by a measurement of the forward-backward asymmetry in untagged B⁰ D^*+ ^- _ decays, and finally, measurements of the branching-fraction ratios R (D^*+₄/) = B (B⁰ D^*+ e^- ₑ) / B (B⁰ D^*+ ^- _), using the same untagged data set, along with the first measurement of the inclusive light-lepton ratio R (X₄/) = B (B X e^- ₑ) /B (B X ^- _). Furthermore, we present two tests of heavy-to-light lepton universality. In the first test, we report the measurement of the branching-fraction ratio R (D^*/) using hadronic tagging. In the second test, we present the first measurement of the inclusive ratio R (X/). All presented results are consistent with their corresponding Standard Model predictions and, where applicable, with the experimental world averages.
H. Junkerkalefeld (Mon,) studied this question.
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