THE END-POINT REGION OF THE ELECTRON SPECTRUM IN INCLUSIVE SEMILEPTONIC HEAVY-QUARK DECAY

The endpoint region of the electron spectrum induced by the quark-level semileptonic decay b to ue nu /sup /e is potentially important for the measurement of the Cabibbo-Kobayashi-Maskawa (CKM) parameter Vub. The endpoint region is crucial to this measurement since, with V ub<<Vcb, only electron energies Ee with (mB2-mD2)/2mB<or approximately=Ee<or=(mB2-mpi 2)/2mB are useful for this purpose: for Ee much below this interval the spectrum is dominated by decays induced by b to ce nu e. However, the extraction of Vub requires that theory be able to calculate the rate d Gamma /dEe in this region apart from the overall factor of mod Vub mod 2 arising from the CKM matrix.