INSTANTONS AND THE END-POINT OF THE LEPTON ENERGY-SPECTRUM IN CHARMLESS SEMILEPTONIC B-DECAYS

A recent calculation by Chay and Rey has shown that instantons may mak e a significant contribution to the lepton energy spectrum near its en d point. Using an ansatz borrowed from the study of high energy baryon -number-violating processes, we investigate whether these corrections could spoil the relation between the nonperturbative contributions to this spectrum and to the photon energy spectrum in radiative B decays. We find, in general, that this universality may well fail unless the spectrum is smeared over a region which is considerably larger than ha d previously been thought necessary. This result affects the possibili ty of performing a reliable measurement of V-ub using inclusive decays .