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

Abstract

By analyzing B→X _u ℓ ν _ℓ spectra with a model based on soft-gluon resummation and an analytic time-like QCD coupling, we obtain

$$|V_{ub}|=(3.76\pm0.13\pm0.22)\times10^{-3},$$

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 $P_{+}\equiv E_{X}-|\vec{p}_{X}|$ , together with the double distributions in (m _X ,q ²) and (E _ℓ ,s ^max_h ), are used to select the phase-space regions. q ² is the dilepton squared momentum and s ^max_h is the maximal m ² _X 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.