890 research outputs found

    Measurement of the B → D̅ ^((*))D^((*))K branching fractions

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    We present a measurement of the branching fractions of the 22 decay channels of the B^0 and B+ mesons to D̅ ^((*))D^((*))K, where the D^((*)) and D̅ ^((*)) mesons are fully reconstructed. Summing the 10 neutral modes and the 12 charged modes, the branching fractions are found to be B(B^0→D̅6((*))D^((*))K)=(3.68 ± 0.10 ± 0.24)% and B(B^+→D̅ ^((*))D^((*))K)=(4.05 ± 0.11 ± 0.28)%, where the first uncertainties are statistical and the second systematic. The results are based on 429  fb^(-1) of data containing 471 × 10^6BB̅ pairs collected at the Υ(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory

    Limits on τ lepton-flavor violating decays into three charged leptons

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    A search for the neutrinoless, lepton-flavor violating decay of the τ lepton into three charged leptons has been performed using an integrated luminosity of 468  fb^(-1) collected with the BABAR detector at the PEP-II collider. In all six decay modes considered, the numbers of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range (1.8–3.3)×10^(-8) at 90% confidence level

    Search for Production of Invisible Final States in Single-Photon Decays of Y(1S)

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    We search for single-photon decays of the Υ(1S) resonance, Υ → γ + invisible, where the invisible state is either a particle of definite mass, such as a light Higgs boson A^0, or a pair of dark matter particles, χχ̅ . Both A^0 and χ are assumed to have zero spin. We tag Υ(1S) decays with a dipion transition Υ(2S)→π^+π^-Υ(1S) and look for events with a single energetic photon and significant missing energy. We find no evidence for such processes in the mass range m_(A^0 ≤ 9.2  GeV and m_χ ≤ 4.5  GeV in the sample of 98×10^6 Υ(2S) decays collected with the BABAR detector and set stringent limits on new physics models that contain light dark matter states

    Studies of τ^- → ηK^-ν-τ and τ^- → ηπ^- ν_τ at BABAR and a search for a second-class current

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    We report on analyses of tau lepton decays τ^- → ηK^-ν_τ and τ^- → ηπ^-ν_τ, with η → π^+π^-π^0, using 470  fb^(-1) of data from the BABAR experiment at PEP-II, collected at center-of-mass energies at and near the Υ(4S) resonance. We measure the branching fraction for the τ^- → ηK^-ν_τ decay mode, B(τ^- → ηK^-ν_τ)=(1.42 ± 0.11(stat) ± 0.07(syst))× 10^(-4), and report a 95% confidence level upper limit for the second-class current process τ^- → ηπ^-ν_τ, B(τ^- → ηπ^-ν_τ)<9.9 × 10^(-5)

    Measurement of D^0-D(overbar)^(0) Mixing Parameters Using D^0 → K_(S)^(0)π^(+)π^(-) and D^0 → K_(S)^(0)K^(+)K^(-) Decays

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    We report a direct measurement of D^0-D(overbar)^0 mixing parameters through a time-dependent amplitude analysis of the Dalitz plots of D^0 → K_(S)^(0)π^(+)π^(-) and, for the first time, D^0 → K_(S)^(0)K^(+)K^(-) decays. The low-momentum pion π^(+)_s in the decay D^(*+)→D^(0)π^(+)_s identifies the flavor of the neutral D meson at its production. Using 468.5 fb^(-1) of e^(+)e^(-) colliding-beam data recorded near √s=10.6  GeV by the BABAR detector at the PEP-II asymmetric-energy collider at SLAC, we measure the mixing parameters x=[1.6±2.3(stat)±1.2(syst)±0.8(model)]×10^(-3), and y=[5.7±2.0(stat)±1.3(syst)±0.7(model)]×10^(-3). These results provide the best measurement to date of x and y. The knowledge of the value of x, in particular, is crucial for understanding the origin of mixing

    Observation of the rare decay B^0 → K_S^(0)K^(±)π^∓

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    We report an analysis of charmless hadronic decays of neutral B mesons to the final state K_(S)^(0)K^(±)π^∓, using a data sample of (465±5)×10^6 BB(overbar) events collected with the BABAR detector at the Υ(4S) resonance. We observe an excess of signal events with a significance of 5.2 standard deviations including systematic uncertainties and measure the branching fraction to be B(B^0 → K_(S)^(0)K^(±)π^∓)=(3.2±0.5±0.3)×10^(-6), where the uncertainties are statistical and systematic, respectively

    Measurement of the γγ^*→η and γγ^*→η^′ transition form factors

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    We study the reactions e^+e^-→e^+e^-η^(′) in the single-tag mode and measure the γγ^*→η^(′) transition form factors in the momentum-transfer range from 4 to 40  GeV^2. The analysis is based on 469  fb^(-1) of integrated luminosity collected at PEP-II with the BABAR detector at e^+e^- center-of-mass energies near 10.6 GeV
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