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208 records were found.

We present a new measurement of the time-dependent CP asymmetry of B^0→D^(*+)D^(*-) decays using (471±5) million BB pairs collected with the BABAR detector at the PEP-II B Factory at the SLAC National Accelerator Laboratory. Using the technique of partial reconstruction, we measure the time-dependent CP asymmetry parameters S = -0.34 ± 0.12 ± 0.05 and C = +0.15 ± 0.09 ± 0.04. Using the value for the CP-odd fraction R_⊥ = 0.158 ± 0.028 ± 0.006, previously measured by BABAR with fully reconstructed B^0→D^(*+)D^(*-) events, we extract the CP-even components S_+= -0.49 ± 0.18 ± 0.07 ± 0.04 and C_+ = +0.15 ± 0.09 ± 0.04. In each case, the first uncertainty is statistical and the second is systematic; the third uncertainty on S_+ is the contribution from the uncertainty on R_⊥. The measured value of the CP-even component S_+ is consistent wi...
The photon spectrum in B → X_sγ decay, where X_s is any strange hadronic state, is studied using a data sample of (382.8±4.2) × 10^6 e^+e^- → Υ(4S) → BB events collected by the BABAR experiment at the PEP-II collider. The spectrum is used to measure the branching fraction B(B → X_sγ)=(3.21±0.15±0.29±0.08) × 10^(-4) and the first, second, and third moments ⟨E_γ⟩=2.267±0.019±0.032±0.003  GeV, ⟨(E_γ-⟨E_γ⟩)^2⟩=0.0484±0.0053±0.0077±0.0005  GeV^2, and ⟨(E_γ-⟨E_γ⟩)^3⟩=-0.0048±0.0011±0.0011±0.0004  GeV^3, for the range E_γ > 1.8  GeV, where E_γ is the photon energy in the B-meson rest frame. Results are also presented for narrower E_γ ranges. In addition, the direct CP asymmetry A_(CP)(B → X_(s+d)γ) is measured to be 0.057±0.063. The spectrum itself is also unfolded to the B-meson rest frame; that is the frame in which theoretical predictions ...
We present a measurement of D^0-D^0 mixing and CP violation using the ratio of lifetimes simultaneously extracted from a sample of D^0 mesons produced through the flavor-tagged process D^(*+)→D^0π^+, where D^0 decays to K^∓π^±, K^-K^+, or π^-π^+, along with the untagged decays D^0→K^∓π^± and D^0→K^-K^+. The lifetimes of the CP-even, Cabibbo-suppressed modes K^-K^+ and π^-π^+ are compared to that of the CP-mixed mode K^∓π^± in order to measure y_(CP) and ΔY. We obtain y_(CP)=[0.72±0.18(stat)±0.12(syst)]% and ΔY=[0.09±0.26(stat)±0.06(syst)]%, where ΔY constrains possible CP violation. The y_(CP) result excludes the null mixing hypothesis at 3.3σ significance. This analysis is based on an integrated luminosity of 468  fb^(-1) collected with the BABAR detector at the PEP-II asymmetric-energy e^+e^- collider.
We search for di-muon decays of a low-mass Higgs boson (A^0) produced in radiative Υ(1S) decays. The Υ(1S) sample is selected by tagging the pion pair in the Υ(2S,3S) → π^+ π^-Υ(1S) transitions, using a data sample of 92.8 × 10^6 Υ(2S) and 116.8 × 10^6 Υ(3S) events collected by the BABAR detector. We find no evidence for A^0 production and set 90% confidence level upper limits on the product branching fraction B(Υ(1S) → γA^0) × B(A^0 → μ^ +μ^-) in the range of (0.28-9.7) × 10^(-6) for 0.212 ≤ m_A^0 ≤ 9.20  GeV/c^2. The results are combined with our previous measurements of Υ(2S,3S) → γA^0, A^0 → μ^+μ^- to set limits on the effective coupling of the b quark to the A^0.
We present a measurement of the B^+ → ωℓ^+ν branching fraction based on a sample of 467 million BB pairs recorded by the BABAR detector at the SLAC PEP-II e+e- collider. We observe 1125±131 signal decays, corresponding to a branching fraction of B(B^+ → ωℓ^+ν)=(1.21±0.14±0.08)×10^(-4), where the first error is statistical and the second is systematic. The dependence of the decay rate on q^2, the invariant mass squared of the leptons, is compared to QCD predictions of the form factors based on a quark model and light-cone sum rules.
We present improved measurements of CP-violation parameters in the decays B^0→π^+π^-, B^0→K^+π^-, and B^0→π^0π^0, and of the branching fractions for B^0→π^0π^0 and B^0→K^0π^0. The results are obtained with the full data set collected at the Υ(4S) resonance by the BABAR experiment at the PEP-II asymmetric-energy B factory at the SLAC National Accelerator Laboratory, corresponding to (467±5)×10^6 BB pairs. We find the CP-violation parameter values and branching fractions: S_(π^+π^-)=-0.68±0.10±0.03, C_(π^+π^-)=-0.25±0.08±0.02, A_(K^-π^+)=-0.107±0.016_(-0.004)^(+0.006), C_(π^0π^0)=-0.43±0.26±0.05, B(B^0→π^0π^0)=(1.83±0.21±0.13)×10^(-6),  B(B^0→K^0π^0)= (10.1±0.6±0.4)×10^(-6), where in each case, the first uncertainties are statistical and the second are systematic. We observe CP violation with a significance of 6.7 standard deviations for...
We report on a search for direct CP violation in the singly Cabibbo-suppressed decay D^+→K^+K^-π^+ using a data sample of 476  fb^(-1) of e^+e^- annihilation data accumulated with the BABAR detector at the SLAC PEP-II electron-positron collider, running at and just below the energy of the Υ(4S) resonance. The integrated CP-violating decay rate asymmetry A_(CP) is determined to be (0.37±0.30±0.15)%. Model-independent and model-dependent Dalitz plot analysis techniques are used to search for CP-violating asymmetries in the various intermediate states. We find no evidence for CP-violation asymmetry.
We report a search for CP violation in the decay modes D^±→K_S^0K^±, D_s^±→K_S^0K^±, and D_s^±→K_S^0π^± using a data set corresponding to an integrated luminosity of 469  fb^(-1) collected with the BABAR detector at the PEP-II asymmetric energy e^+e^- storage rings. The decay rate CP asymmetries, A_(CP), are determined to be (+0.13±0.36(stat)±0.25(syst))%, (-0.05±0.23(stat)±0.24(syst))%, and (+0.6±2.0(stat)±0.3(syst))%, respectively. These measurements are consistent with zero, and also with the Standard Model prediction [(-0.332±0.006)% for the D^±→K_S^0K^± and D_s^±→K_S^0K^± modes, and (+0.332±0.006)% for the D_s^±→K_S^0π^± mode]. They are the most precise determinations to date.
We report the determination of the Cabibbo-Kobayashi-Maskawa CP-violating angle γ through the combination of various measurements involving B^± → DK^±, B^± → D^*K^±, and B^± → DK^(*±) decays performed by the BABAR experiment at the PEP-II e^+e^- collider at SLAC National Accelerator Laboratory. Using up to 474 million BB pairs, we obtain γ=(69_(-16)^(+17))° modulo 180°. The total uncertainty is dominated by the statistical component, with the experimental and amplitude-model systematic uncertainties amounting to ±4°. The corresponding two-standard-deviation region is 41° < γ < 102°. This result is inconsistent with γ=0 with a significance of 5.9 standard deviations.
The ratio R_(τμ)(Υ(1S)) = Γ_(Υ(1S)→τ^+^τ-)/Γ_(Υ(1S)→μ^+μ^-) is measured using a sample of (121.8±1.2) × 10^(6)Υ(3S) events recorded by the BABAR detector. This measurement is intended as a test of lepton universality and as a search for a possible light pseudoscalar Higgs boson. In the standard model (SM) this ratio is expected to be close to 1. Any significant deviations would violate lepton universality and could be introduced by the coupling to a light pseudoscalar Higgs boson. The analysis studies the decays Υ(3S)→Υ(1S)π^+π^-, Υ(1S)→l^+l^-, where l = μ, τ. The result, R_(τμ)(Υ(1S)) = 1.005±0.013(stat)±0.022(syst), shows no deviation from the expected SM value, while improving the precision with respect to previous measurements.
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