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We report a measurement of the inclusive charmless semileptonic branching fraction of B mesons in a sample of 89 million B[bar B] events recorded with the BABAR detector at the[Upsilon](4S) resonance. Events are selected by fully reconstructing the decay of one B meson and identifying a charged lepton from the decay of the other B meson. The number of signal events is extracted from the hadronic mass distribution and is used to determine the ratio of branching fractions[Beta]([bar B][yields] X[sub u]l[bar[nu]])/[Beta]([bar B][yields] Xl[bar[nu]])= (2.06[+-] 0.25(stat)[+-] 0.23(syst)[+-] 0.36(theo)) x 10[sup -2]. Using the measured branching fraction for inclusive semileptonic B decays, we find[Beta]([bar B][yields] X[sub u]l[bar[nu]])= (2.24[+-] 0.27(stat)[+-] 0.26(syst)[+-] 0.39(theo)) x 10[sup -3] and derive the CKM matrix elementV[sub ub]= (4.62[+-] 0.28(stat)[+-] 0.27(syst)[+-] 0.48(theo)) x 10[sup -3].
We report a measurement of the inclusive charmless semileptonic branching fraction of B mesons in a sample of 89 million B{bar B} events recorded with the BABAR detector at the [Upsilon](4S) resonance. Events are selected by fully reconstructing the decay of one B meson and identifying a charged lepton from the decay of the other B meson. The number of signal events is extracted from the hadronic mass distribution and is used to determine the ratio of branching fractions [Beta]({bar B} → X{sub u}l{bar {nu}})/[Beta]({bar B} → Xl{bar {nu}}) = (2.06 ± 0.25(stat) ± 0.23(syst) ± 0.36(theo)) x 10−2. Using the measured branching fraction for inclusive semileptonic B decays, we find [Beta]({bar B} → X{sub u}l{bar {nu}}) = (2.24 ± 0.27(stat) ± 0.26(syst) ± 0.39(theo)) x 10−3 and derive the CKM matrix element.
An algorithm for identification of electrons with the BABAR detector is developed. Based on pure samples of electrons and hadrons obtained from data, we determine the electron identification efficiency to be above 90% for momenta above 0.5 GeV/c in the laboratory frame, while the pion fake rate lies between 0.05% and 0.1%. Based on this algorithm, a measurement of the inclusive lepton momentum spectrum in B meson decays is performed. We analyze 4.13 fb^-1 and 0.97 fb^-1 of data recorded at and slightly below the Upsilon(4S) resonance with the BABAR detector at the PEP-II a symmetric B-Factory. B-Bbar events are tagged by a high momentum electron. Using charge and angular correlations, leptons from a second semileptonic $B$ decay are separated from secondary charm semileptonic decays. The inclusive branching ratio is measured to be (10.85 +-0.22(stat.) +-0.34(sys))% . Combined with the B lifetime we determine |V_cb| = 0.0406 +-0.0009(exp) +-0.0019(theory).
The BABAR experiment at SLAC provides an opportunity for measurement of the Standard Model parameters describing CP violation. A method of measuring the CKM matrix element.
The authors report the first measurement of the branching fraction f00 for?(4S) → B°{bar B}°. The data sample consists of 81.7 fb−1 collected at the?(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy ee− storage ring. Using partial reconstruction of the decay {bar B}° → D*+l− {bar?}{sub t} in which only the charged lepton and the soft pion from the decay D*+ → D°?+ are reconstructed, they obtain f00 = 0.487 ± 0.010(stat) ± 0.008(sys). The result does not depend on the branching fractions of {bar B}° → D*+l− {nu}{sub t} and D*+ → D°?+ decays, on the ratio of the charged and neutral B meson lifetimes, nor on the assumption of isospin symmetry.