Abstract
I review currently discussed methods to determine the CKM mixing matrix element
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ub
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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→πeν
, seem slightly more accurate and allow determination of
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from the spectrum in the momentum transfer to the leptons with a theoretical uncertainty of
∼10
.