V-UB FROM THE HADRON ENERGY-SPECTRUM IN INCLUSIVE SEMILEPTONIC B-DECAYS

A measurement of the hadron energy spectrum in inclusive semileptonic B decays is proposed as a viable method for extracting \V-ub\. Compare d to the traditional energy spectrum of the charged lepton, the hadron a energy spectrum exhibits kinematical advantages such as a wider ene rgy window and a larger signal branching fraction. The hadron energy d istribution is calculated in the approach of the model of Altarelli et al. and of the heavy-quark effective field theory. In both methods, p erturbative QCD corrections, the Fermi motion of the b quark in the B meson, and the recoil momentum of the B meson [stemming from the Y(4S) resonance] are taken into account. We find excellent agreement betwee n the spectra calculated in both methods, especially in the relevant k inematical region below the charmed meson threshold. The theoretical e rror to \V-ub\, which is dominated by the uncertainty of the b-quark m ass, is estimated to be at the +/-12% level. Experimental techniques u tilized in the recent measurement of exclusive semileptonic b-->u deca ys point to the feasibility of the present proposal both at CLEO and a t future B factories.