Semileptonic decays of B mesons

We have studied the production of B mesons in e/sup +/e/sup -/ annihilations and present new measurements of the semileptonic branching fractions for B-meson decay. We find B(B..-->..e..nu..X) = 0.127 +- 0.017 +- 0.013 and B(B..--> mu nu..X) = 0.122 +- 0.017 +- 0.031, where the errors are statistical and systematic, respectively. The observed lepton momentum spectra from B decays are presented. From these spectra we find the mean hadronic mass (M/sub X/) recoiling against the detected lepton to be M/sub X/ = 2.2 +- 0.2 GeV/c/sup 2/. We have also observed an enhancement in the lepton yield from the continuum above BB-bar threshold. This enhancement is interpreted as continuum B production and is consistent with what is expected from the naive quark model.