65 research outputs found

    Reevaluation of the hadronic contribution to the muon magnetic anomaly using new e+e- -> pi+pi- cross section data from BABAR

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    Using recently published, high-precision pi+pi- cross section data by the BABAR experiment from the analysis of e+e- events with high-energy photon radiation in the initial state, we reevaluate the lowest order hadronic contribution a_mu[had,LO] to the anomalous magnetic moment of the muon. We employ newly developed software featuring improved data interpolation and averaging, more accurate error propagation and systematic validation. With the new data, the discrepancy between the e+e- and tau-based results for the dominant two-pion mode reduces from previously 2.4 sigma to 1.5 sigma in the dispersion integral, though significant local discrepancies in the spectra persist. We obtain for the e+e- based evaluation amu[had,LO] = (695.5 +- 4.1) 10^-10, where the error accounts for all sources. The full Standard Model prediction of a_mu differs from the experimental value by 3.2 sigma.Comment: 9 pages, 7 figures. Version published in Eur. Phys. J. C. The theory vs. experiment discrepancy increased by 0.1 \sigma, using the updated experimental g-2 value with the new \mu_\mu/\mu_p rati

    Measurement of ϕ\phi(1020) meson leptonic width with CMD-2 detector at VEPP-2M Collider

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    The ϕ\phi(1020) meson leptonic width has been determined from the combined analysis of 4 major decay modes of the resonance (ϕK+K,KL0KS0,π+ππ0,ηγ\phi\to K^+ K^-,K^0_LK^0_S,\pi^+\pi^-\pi^0,\eta\gamma) studied with the CMD-2 detector at the VEPP-2M e+ee^+e^- collider. The following value has been obtained: Γ(ϕe+e)=1.235±0.006±0.022\Gamma(\phi\to e^+e^-) = 1.235\pm 0.006\pm 0.022 keV. The ϕ(1020)\phi(1020) meson parameters in four main decay channels have been also recalculated: B(ϕK+K)=0.493±0.003±0.007B(\phi\to K^+K^-) = 0.493\pm 0.003\pm 0.007, B(ϕKLKS)=0.336±0.002±0.006B(\phi\to K_LK_S) = 0.336\pm 0.002\pm 0.006, B(ϕπ+ππ0)=0.155±0.002±0.005B(\phi\to\pi^+\pi^-\pi^0) = 0.155\pm 0.002\pm 0.005, B(ϕηγ)=0.0138±0.0002±0.0002B(\phi\to\eta\gamma) = 0.0138\pm 0.0002\pm 0.0002.Comment: 14 pages, 3 figure

    Study of the radiative decay ϕηγ\phi \to \eta \gamma with CMD-2 detector

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    Using the 1.9pb11.9 pb^{-1} of data collected with the CMD-2 detector at VEPP-2M the decay mode ϕηγ\phi \to \eta \gamma, ηπ+ππ0\eta \to \pi^+\pi^-\pi^0 has been studied. The obtained branching ratio is B(ϕηγ)=(1.18±0.03±0.06)\phi \to \eta \gamma) = (1.18 \pm 0.03 \pm 0.06) %.Comment: 13 pages, 5 figures, LaTex2e, to be published in Phys. Lett.

    Observation of KS0K_S^0 semileptonic decays with CMD-2 detector

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    The decay KS0πeνK_S^0 \to \pi e \nu has been observed by the CMD-2 detector at the e^+e^- collider VEPP-2M at Novosibirsk. Of 6 million produced KL0KS0K_L^0K_S^0 pairs, 75±1375 \pm 13 events of the KS0πeνK_S^0 \to \pi e \nu decay were selected. The corresponding branching ratio is B(KS0πeν)=(7.2±1.4)×104B(K_S^0 \to \pi e \nu)=(7.2 \pm 1.4)\times10^{-4}. This result is consistent with the evaluation of B(KS0πeν)B(K_S^0 \to \pi e \nu) from the KL0K_L^0 semileptonic rate and KS0K_S^0 lifetime assuming ΔS=ΔQ\Delta S=\Delta Q .Comment: 7 pages, 6 figures, LaTex2e. Submitted to Phys.Lett.

    Measurement of omega meson parameters in pi^+pi^-pi^0 decay mode with CMD-2

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    About 11 200 e^+e^- -> omega -> pi^+pi^-pi^0 events selected in the center of mass energy range from 760 to 810 MeV were used for the measurement of the \omega meson parameters. The following results have been obtained: sigma _{0}=(1457 \pm 23 \pm 19)nb, m_{\omega}=(782.71 \pm 0.07 \pm 0.04) MeV/c^{2}, \Gamma_{\omega}=(8.68 \pm 0.23 \pm 0.10) MeV, \Gamma_{e^+e^-}\cdot Br (\omega -> pi^+pi^-pi^0)= (0.528 \pm 0.012 \pm 0.007) \cdot 10^{-3} MeV.Comment: 8 pages, 4 figure

    Study of the Process e+eKL0KS0e^+e^- \to K^0_L K^0_S in the C.M.Energy Range 1.05-1.38 GeV with CMD-2

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    The process e+eKL0KS0e^+e^- \to K^0_L K^0_S has been studied with the CMD-2 detector using about 950 events detected in the center-of-mass energy range from 1.05 to 1.38 GeV. The cross section exceeds the expectation based on the contributions of the rho(770), omega(782) and phi(1020) mesons only.Comment: 12 pages, 3 figures, uses elsart.cls, submitted to Physics Letters

    Cross section of the reaction e+eπ+ππ+πe^+ e^- \to \pi^+\pi^-\pi^+\pi^- below 1 GeV at CMD-2

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    Using 3.07 pb1{pb}^{-1} of data collected in the energy range 0.60-0.97 GeV by CMD-2, about 150 events of the process \epm \to \pch have been selected. The energy dependence of the cross section agrees with the assumption of the a1(1260)πa_1(1260) \pi intermediate state which is dominant above 1 GeV. For the first time \fourpi events are observed at the ρ\rho meson energy. Under the assumption that all these events come from the ρ\rho meson decay, the value of the cross section at the ρ\rho meson peak corresponds to the following decay width: \Gamma(\rho^0 \to \fourpi) = (2.8 \pm 1.4 \pm 0.5) {keV} or to the branching ratio B(\rho^0 \to \fourpi) = (1.8 \pm 0.9 \pm 0.3) \cdot 10 ^{-5}.Comment: 15 pages, 5 figure
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