Complementary Observables for the Determination of |Vub | in

The determination of |Vub | from inclusive semileptonic B decays is limited by uncertainties in mod-eling the decay distributions in b → uν 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 paper 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 quan-tities two complementary observables can be constructed, one for discriminating between b → uν transitions and background and the other for constraining the shape function. Using this technique the uncertaintites in |Vub | from the shape function may be signficantly reduced. Submitted to Physics Letters