Kazuki Kojima

17 July 2023

Abstract: We report two new measurements for tests of lepton flavor universality between electrons and muons using semileptonic $B$ decays with a data set of $189~\mathrm{fb}^{-1}$ collected at the Belle II experiment between 2019 and 2021. Firstly, we find a ratio of inclusive branching fractions at $R(X_{e/\mu}) \equiv \mathcal{B}(\overline{B} \rightarrow Xe^{-}\overline{\nu}_{e})/\mathcal{B}(\overline{B} \rightarrow X\mu^{-}\overline{\nu}_{\mu}) = 1.007 \pm 0.009 (\mathrm{stat.}) \pm 0.019 (\mathrm{syst.})$. This inclusive measurement leads to the most precise universality test based on branching fractions. The measured $R(X_{e/\mu})$ is consistent with the Standard-Model prediction. Secondly, we measure a comprehensive set of five angular asymmetries of $\overline{B}^{0} \rightarrow {D^{*}}^{+}\ell^{-}\overline{\nu}_{\ell}$ decays and obtain agreements with the Standard Model for the measured asymmetries and their differences at a $p$-value above $13\%$. From both tests, no evidence of lepton universality violation is found.

Keyword(s): Semileptonic ; Semileptonic B decays ; R(X) ; Angular asymmetry ; Afb ; LFV ; LFUV ; FEI ; R(D*) ; Moriond ; MoriondEW ; MoriondEWK ; Moriond EW ; Moriond EWK ; Moriond2023
Note: Contribution to the 2023 Electroweak session of the 57th Rencontres de Moriond