Measurement ofB-Meson Semileptonic Decay

Abstract

Using the Colubia University—Stony Brook detector we have measured the production of energetic electrons ($E>\mathrm{}1\mathrm{}$ GeV) in $e^{+}{e}^{-}$ annihilations in the center-of-mass energy range 10.4 to 11.4 GeV. We observe an enhanced electron signal at the ${\Upsilon }^{\prime \prime \prime }\mathrm{}\left(4S\right)\mathrm{}$ resonance, which we interpret as evidence for the $\beta$ decay of a new flavor of quark, $b$, bound within a new flavor meson, $B$. We derive a branching ratio for $B\to \mathrm{Xe}\nu$ of (13.6 ± 2.5 ± 3)%. The observed energy spectrum of the electrons favors the decay $b\to \mathrm{ce}\nu$ over $b\to \mathrm{ue}\nu$.