Factorization for Power Corrections to B->Xs gamma and B-> Xu e nu

Abstract

We derive factorization theorems for Lambda_QCD/mb power corrections to inclusive B-decays in the endpoint region, where mX^2 ~mb Lambda_QCD. In B-> Xu e nu our results are for the full triply differential rate. A complete enumeration of Lambda_QCD/mb corrections is given. We point out the presence of new Lambda_QCD/mb-suppressed shape functions, which arise at tree level with a $4 pi$-enhanced coefficient, and show that these previously neglected terms induce an additional large uncertainty for current inclusive methods of measuring |Vub| that depend on the endpoint region of phase space.