Measurement of Inclusive b Semileptonic Branching Fractions at the Z Resonance

This document presents a new measurement of inclusive b semileptonic branching fractions B(b-->l) and B(b-->c-->l). The b-->l and b-->c-->l are separated by a means that uses correlation between the final state lepton charge and that of its parent b quark as a constraint. Monte Carlo counts of electrons and muons are calibrated to the data using a newly developed technique based on pairs of mutually independent tests for each particle hypothesis separately. The data sample consists of about 550,000 hadronic Z decays collected at the SLD between 1993 and 1998. Upon analysis of electron and muon counts in 61602 hadronic event hemispheres tagged as containing either a b or a b-bar, the author reports: B(b-->e) = 0.0949{+-}0.0049{+-}0.0050, B(b-->mu) = 0.1066{+-}0.0038{+-}0.0049, combined B(b-->l) = 0.1015{+-}0.0030{+-}0.0035; and B(b-->c-->e) = 0.0811{+-}0.0053{+-}0.0030, B(-->b-->c-->mu) = 0.0717{+-}0.0045{+-}0.0024, combined B(b-->c-->l) = 0.0756{+-}0.0034{+-}0.0019.