A Model independent determination of the inclusive semileptonic decay fraction of B mesons

Abstract With the ARGUS detector at the e + e - storage ring DORISII, we have determined decay fraction and electron momentum spectrum of the inclusive decay mode B → eν X. Usinng lepton tags from the second B meson. in 209 000 γ(4 S ) → B B decays, we could determine the spectrum for all electron momenta p e > 0.6 GeV/ c . Including the small extrapolation to p e > 0, we find the model-independent decay fraction B (B → eν X) = (9.6 ± 0.5 ± 0.4)%. Adding D mesontags, our result is (9.7 ± 0.5 ± 0.4)%.