BELLE2-CONF-PH-2022-004

Test of lepton flavor universality in inclusive semileptonic B decays at Belle II

Abstract: We present the measurement of the ratio of branching fractions of inclusive semileptonic \B decays, $\RXemu=\BFXenu/\BFXmunu$, with a hadronic tagged analysis using \lumion of \belletwo data. We find $\RXemu = 1.033 \pm 0.010 \pm 0.020$. The errors quoted correspond to the statistical and systematic uncertainties, respectively. This represents the most precise single test of $e - \mu$ flavor universality in semileptonic \B decays and agrees with the Standard Model expectation within less than $1.5\sigma$. This analysis paves the path to the measurement of $\RX=\BFXtaunu/\BFXellnu$ at \belletwo.

Keyword(s): Belle II ; semitauonic decays ; semileptonic decays ; lepton flavor universality

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