Kazuki Kojima

10 July 2023

Abstract: We report two novel 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 ratios 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 ratios. 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 asymmetries at a $p$-value more than $13\%$. From both tests, no evidence of the universality violation is found.

Keyword(s): Semileptonic ; Semileptonic B decays ; R(X) ; Angular asymmetry ; Afb ; LFV ; LFUV ; FEI ; Moriond ; MoriondEW ; MoriondEWK ; Moriond EW ; Moriond EWK ; Moriond2023
Note: Page limit: 4 pages https://moriond.in2p3.fr/2023/EW/Contributions.html