Inclusive spectra in charmless semileptonic B decays by dressed gluon exponentiation

The triple differential spectrum in \bar{B} -> X_u l \bar{\nu} is computed byDressed Gluon Exponentiation (DGE). In this framework the on-shell calculation,converted into hadronic variables, can be directly used as an approximation tothe meson decay spectrum, without involving a leading-power non-perturbativefunction. Sudakov resummation for the fully differential \bar{B} -> X_u l\bar{\nu} width is formulated in moment space, where moments are defined usingthe ratio between the lightcone momentum components of the partonic jet p^+/p^-and the hard scale is p^-. In these variables the correspondence with the\bar{B} -> X_s \gamma case is transparent. The Sudakov exponent is known tonext-to-next-to-leading logarithmic accuracy. Further constraints are put onits Borel sum using the cancellation of the leading renormalon ambiguity andthe absence of the next-to-leading one, which was proven in the large-beta_0limit and assumed here to be general. Based on the resummed spectrum, matchedto the fully differential NLO result, we calculate the event fractionassociated with experimental cuts on the hadronic mass (or the small lightconecomponent) as well as on the lepton energy. Finally, we extract |V_ub| fromrecent measurements by Belle and analyze the theoretical uncertainty.Comment: v1: 61 pages, 14 figures; v2: 63 pages, 14 figures. Extended discussion on non-perturbative effects in Sections 1.2, 3.4, 4.1 and 4.2. Added references. To be published in JHE