Inclusive Measure of |V_ub| with the Analytic Coupling Model

TL;DR

This paper presents a new inclusive measurement of |V_ub| using a model based on soft-gluon resummation and an analytic QCD coupling, achieving results consistent with other methods and highlighting the impact of threshold modeling.

Contribution

It introduces an analytic coupling model for inclusive |V_ub| extraction from B decay spectra, providing a more comprehensive phase-space analysis and addressing previous discrepancies.

Findings

Measured |V_ub| = (3.76 +- 0.13 +- 0.22) x 10^(-3)

Results agree with exclusive decay measurements and SM fits

Discrepancies with previous inclusive results are due to threshold modeling

Abstract

By analyzing B -> X_u l nu_l spectra with a model based on soft-gluon resummation and an analytic time-like QCD coupling, we obtain |V_ub| = (3.76 +-0.13 +- 0.22)*10^(-3), where the first and the second error refers to experimental and theoretical errors, respectively. 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_+ = E_X - p_X, together with the double distributions in (m_X,q^2) and (E_l,s_h^max), are used to select the phase-space regions. The 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 +2 sigma) with respect to previous inclusive measurements is not related to different choices for the b (and c) masses but to a different modelling of the threshold (Sudakov) region.