Speaker
Description
We report the measurement of the partial branching fraction of $B \to X_u \ell \bar \nu_\ell$ over $B \to X_c \ell \bar \nu_\ell$ using the complete Belle data set of 711 fb${}^{-1}$. We reconstruct collision events where one B meson is fully reconstructed in hadronic modes using the full-event-interpretation algorithm, developed for Belle II. This allows for the reconstruction of the hadronic $X_u$ system associated with the semileptonic $b \to u \ell \bar\ nu_\ell$ decay. We further perform the first simultaneous determination of the absolute value of the CKM matrix element $V_{ub}$ by leveraging both inclusive and exclusive decays with the complete Belle data set using a similar technique. To disentangle exclusive $B \to \pi \ell \bar \nu_\ell$ decays from other inclusive $B \to X_u \ell \bar \nu_\ell$ events and backgrounds, we employ a two-dimensional fit that utilizes the charged pion multiplicity in the $X_u$ system and the four-momentum transfer $q^2$ between the $B$ and $X_u$ system. Both results provide new insights in the tension of the value of $V_{ub}$ between inclusive and exclusive determinations.
| Collaboration / Activity | Belle Collaboration |
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