Complementary observables for the determination of |Vub| in inclusive semileptonic B decays

The determination of |Vub| from inclusive semileptonic B decays is limited by uncertainties in modeling the decay distributions in b→uℓν transitions. The largest uncertainties arise from the limited knowledge of the appropriate b quark mass and Fermi momentum to use in the parameterization of the shape function. This Letter presents a new method in which these shape function parameters are constrained by the same data used to measure |Vub|. The method requires measurements of the momenta of both the charged lepton and the neutrino in semileptonic B decays. From these quantities two complementary observables can be constructed, one for discriminating between b→uℓν transitions and background and the other for constraining the shape function. Using this technique the uncertainties in |Vub| from the shape function may be significantly reduced.