The most promising ways to measure V_ub

Abstract

I review currently discussed methods to determine the CKM mixing matrix element $|V_{ub}|$ from experimental data. Although the theory of inclusive decays and their spectra has entered a model-independent stage, its predictions are still sensitive to various input parameters, in particular the poorly known $b$ quark mass. At present, determinations from exclusive channels, notably $B\to\pi e \nu$, seem slightly more accurate and allow determination of $|V_{ub}|$ from the spectrum in the momentum transfer to the leptons with a theoretical uncertainty of $\sim 10%$.