A measurement of the semileptonic decay of B mesons into muons

Abstract We have observed muons from the semileptonic decay B → Xμν where B meson are produced in e + e − annihilations into hadrons at the γ(4S) resonance (10.58 GeV). We obtain a branching ratio of (11.2 ± 0.9 ± 1.0)% for B → Xμν. We have also measured the production of energetic muons in hadronic e + e − annihilations in the energy region above the γ(4S) from 10.6 GeV to 11.2 GeV.