RESUMMATION OF NONPERTURBATIVE CORRECTIONS TO THE LEPTON SPECTRUM IN INCLUSIVE B-]X(Q)L(NU)OVER-BAR DECAYS

We apply the operator product expansion to resum the leading nonpertur bative corrections to the end-point region of the lepton spectrum iu i nclusive semileptonic B --> X(q)lnuBAR decays, taking into account a f inite quark mass m(q) in the final state. We show that for both b --> c and b --> u transitions it is consistent to describe these effects b y a convolution of the parton-model spectrum with a universal light-co ne structure function. The moments of this function are proportional t o forward matrix elements of higher-dimension operators. The dominant subleading corrections to our results are of order m(c)/m(b) for b --> c transitions, and of order LAMBDA(QCD)/m(b) for b --> u decays. The prospects for an extraction of the structure function from a measureme nt of the lepton spectrum are discussed.