Speaker
Description
Determinations of the magnitude of the CKM element $|V_{ub}|$ by exclusive and inclusive decays are currently at odds by about three standard deviations. In this talk we report new and updated results on charmless semileptonic $B$ decays, based on the large data sample accumulated by the Belle experiment at the KEKB asymmetric-energy $e^+ e^-$ collider at KEK, Japan, which might help to clarify the experimental situation.
We also report the first absolute measurement of ${\cal B}(B_s \to D_s X)$ via tagging at the $\Upsilon(10860)$ resonance at Belle. The tagging of $B_s^{(*)} B_s^{(*)}$ events is obtained through reconstruction of semileptonic $B_s \to D_s X \ell \nu$ events. Previous measurements of this branching fraction are limited by model-dependence or large statistical uncertainties; a model-independent measurement enables improvements to the precision of the fraction $f_s$ of $B_s$ events at the $\Upsilon(10860)$ and anchors branching fractions of other $B_s$ decays.
