Semileptonic $B$ decays from Belle and Belle II

Abstract

This report summarizes recent measurements of the CKM matrix elements $|V_{cb}|$, $|V_{ub}|$, and lepton-flavor universality tests in semileptonic B decays from the Belle and Belle~II experiments. The decay branching factions $R(D^{*})$ and $R(X)$ are measured with the Belle~II early dataset and the results are found to be consistent with the Standard Model predictions. From a simultaneous measurement of untagged $B^0 \to \pi^{-} \ell^{+} \nu$ and $B^{+} \to \rho^0 \ell^{+} \nu$, the $|V_{ub}|$ value is determined incorporating external theoretical constraints on the decay form factors. The first measurement of the full angular coefficients for $B \to D^* \ell \nu$ decays at Belle provides comprehensive information for determining the decay form factors and $|V_{\mathrm{cb}}|$. This presentation also includes measurements of the ratios $|V_{ub}|^{\mathrm{excl}}/|V_{ub}|^{\mathrm{incl}}$ and $|V_{ub}|^{\mathrm{incl}}/|V_{cb}|^{\mathrm{incl}}$.