Inclusive measure of |V ub | with the analytic coupling model

By analyzing B→X u ℓνℓ spectra with a model based on soft-gluon resummation and an analytic time-like QCD coupling, we obtain |V ub|=(3.76pm0.13pm0.22)×10-3, where the first and the second error refer to experimental and theoretical error, respectively. This model successfully describes the accurate experimental data in beauty fragmentation, which has similar soft-gluon effects. The |V ub | value is obtained from the available measured semileptonic branching fractions in limited regions of the phase space. The distributions in the lepton energy E ℓ , the hadron invariant mass m X , the light-cone momentum P+ ≡ Ex-|pX|, together with the double distributions in (m X ,q 2) and (E ℓ ,s h max), are used to select the phase-space regions. q 2 is the dilepton squared momentum and s h max is the maximal m X 2 at fixed q 2 and E ℓ . The |V ub| value obtained is in complete agreement with the value coming from exclusive B decays and from an over-all fit to the standard model parameters. We show that the slight disagreement (up to +2σ) with respect to previous inclusive measurements is not related to different choices for the b (and c) masses, but to a different modeling of the threshold (Sudakov) region. © 2008 Springer-Verlag / Società Italiana di Fisica.