Semileptonic $B$ decays from Belle and Belle II

TL;DR

This paper reviews recent measurements of CKM matrix elements and lepton-flavor universality in semileptonic B decays from Belle and Belle II, confirming consistency with the Standard Model and providing new insights into decay form factors.

Contribution

It presents new measurements of decay ratios, angular coefficients, and CKM elements, enhancing understanding of B decay dynamics and testing the Standard Model.

Findings

Results are consistent with Standard Model predictions.

First measurement of full angular coefficients for B to D* l nu decays.

Determination of |V_ub| incorporating decay form factors.

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 $|V_{ub}|^{\mathrm{incl}}/|V_{cb}|^{\mathrm{incl}}$.