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

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

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

Study of B → πlν and B → ρlν decays and determination of |V_(ub)|

We present an analysis of exclusive charmless semileptonic B-meson decays based on 377 × 10^6 BB̅ pairs recorded with the BABAR detector at the Υ(4S) resonance. We select four event samples corresponding to the decay modes B^0 → π^-ℓ^+ν, B^+ → π^0ℓ^+ν, B^0 → ρ^-ℓ^+ν, and B^+ → ρ^0ℓ^+ν and find the measured branching fractions to be consistent with isospin symmetry. Assuming isospin symmetry, we combine the two B → πℓν samples, and similarly the two B → ρℓν samples, and measure the branching fractions B(B^0→π^-ℓ^+ν)=(1.41 ± 0.05 ± 0.07) × 10^(-4) and B(B^0 → ρ^-ℓ^+ν)=(1.75 ± 0.15 ± 0.27) × 10^(-4), where the errors are statistical and systematic. We compare the measured distribution in q^2, the momentum transfer squared, with predictions for the form factors from QCD calculations and determine the Cabibbo-Kobayashi-Maskawa matrix element |V_(ub)|. Based on the measured partial branching fraction for B → πℓν in the range q^2 < 12  GeV^2 and the most recent QCD light-cone sum-rule calculations, we obtain |V_(ub)|=(3.78 ± 0.13^(+0.55)_(-0.40)) × 10^(-3), where the errors refer to the experimental and theoretical uncertainties. From a simultaneous fit to the data over the full q^2 range and the FNAL/MILC lattice QCD results, we obtain |V_(ub)|=(2.95 ± 0.31) × 10^(-3) from B → πℓν, where the error is the combined experimental and theoretical uncertainty

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

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

Measurement of the γγ^*→η_c transition form factor

We study the reaction e^+e^-→e^+e^-η_c, η_c→K_SK^±π^∓ and obtain η_c mass and width values 2982.2±0.4±1.6  MeV/c^2 and 31.7±1.2±0.8  MeV, respectively. We find Γ(η_c→γγ)B(ηc→KK π)=0.374±0.009±0.031  keV, and measure the γγ^*→η_c transition form factor in the momentum transfer range from 2 to 50  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

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

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

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