Semileptonic decays ofBmesons
Abstract
We have studied the production of $B$ mesons in ${e}^{+}{e}^{\ensuremath{-}}$ annihilations and present new measurements of the semileptonic branching fractions for $B$-meson decay. We find $B(B\ensuremath{\rightarrow}e\ensuremath{\nu}X)=0.127\ifmmode\pm\else\textpm\fi{}0.017\ifmmode\pm\else\textpm\fi{}0.013$ and $B(B\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\nu}X)=0.122\ifmmode\pm\else\textpm\fi{}0.017\ifmmode\pm\else\textpm\fi{}0.031$, 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 (${M}_{X}$) recoiling against the detected lepton to be ${M}_{X}=2.2\ifmmode\pm\else\textpm\fi{}0.2$ GeV/${\mathit{c}}^{2}$. We have also observed an enhancement in the lepton yield from the continuum above $B\overline{B}$ threshold. This enhancement is interpreted as continuum $B$ production and is consistent with what is expected from the naive quark model.