4,583 research outputs found

    New Results on the Hadronic Contributions to alpha(M_Z) and to (g-2)_mu

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    We reevaluate the dispersion integrals of the leading order hadronic contributions to the running of the QED fine structure constant alpha(s) at s=M_Z^2, and to the anomalous magnetic moments of the muon and the electron. Finite-energy QCD sum rule techniques complete the data from e+e- annihilation and tau decays at low energy and at the cc-bar threshold. Global quark-hadron duality is assumed in order to resolve the integrals using the Operator Product Expansion wherever it is applicable. We obtain delta_alpha_had(M_Z) = (276.3 +/- 1.6)x10^{-4} yielding alpha^{-1}(M_Z) = 128.933 +/- 0.021, and a_mu^had = (692.4 +/- 6.2)x10^{-10} with which we find for the complete Standard Model prediction a_mu^SM = (11659159.6 +/- 6.7)x10^{-10}. For the electron, the hadronic contribution reads a_e^had = (187.5 +/- 1.8)x10^{-14}.Comment: 16 pages, 3 figure

    Two-photon exchange model for production of neutral meson pairs in e+e- annihilation

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    A vector-dominance two-photon exchange model is proposed to explain the recently observed production of ρ0ρ0\rho^0\rho^0 and ρ0ϕ\rho^0\phi pairs in e+ee^+e^- annihilation at 10.58 GeV with the BaBar detector. All the observed features of the data --angular and decay distributions, rates-- are in agreement with the model. Predictions are made for yet-unobserved final states.Comment: 7 pages, 2 figures, 1 tabl

    Recent progress on isospin breaking corrections and their impact on the muon g-2 value

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    We describe some recent results on isospin breaking corrections which are of relevance for predictions of the leading order hadronic contribution to the muon anomalous magnetic moment (amuhadLO) when using tau lepton data. When these corrections are applied to the new combined data on the pi^+pi^0 spectral function, the prediction for amuhadLO based on tau lepton data gets closer to the one obtained using e^+e^- data.Comment: 6 pages, 3 figures, Proceedings of the PhiPsi09 Workshop, Oct. 13-16, 2009, Beijing, China. Some typos corrected, and the FSR correction used in a previous work is added to Table

    The hadronic contribution to (g2)μ(g-2)_\mu

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    The evaluation of the hadronic contribution to the muon magnetic anomaly aμa_\mu  is reviewed, including a new estimate using precise results on the π+π\pi^+\pi^- spectral function from the KLOE Collaboration. It is found that the KLOE data confirm to some extent the previous e+ee^+e^- annihilation data in this channel, and accentuate the disagreement with the isospin-breaking-corrected spectral function from τπ+π0ντ\tau^-\to\pi^+\pi^0\nu_\tau decays. Correcting for the empirical difference in the mass of the charged and the neutral ρ\rho locally improves, but does not resolve this discrepancy. A preliminary reevaluation (including the KLOE data) of the e^+e-^-based Standard Model prediction of aμa_\mu  results in a deviation of 2.7 standard deviations from the BNL measurement

    Updated Estimate of the Muon Magnetic Moment Using Revised Results from e+e- Annihilation

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    A new evaluation of the hadronic vacuum polarization contribution to the muon magnetic moment is presented. We take into account the reanalysis of the low-energy e+e- annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between e+e- and tau spectral functions in the pi pi channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and 1.0 GeV, so that we refrain from averaging the two data sets. The values found for the lowest-order hadronic vacuum polarization contributions are a_mu[had,LO] = (696.3 +- 6.2[exp] +- 3.6[rad])e-10 (e+e- -based) and a_mu[had,LO] = (711.0 +- 5.0[exp] +- 0.8[rad] +- 2.8[SU2])e-10 (tau-based), where the errors have been separated according to their sources: experimental, missing radiative corrections in e+e- data, and isospin breaking. The corresponding Standard Model predictions for the muon magnetic anomaly read a_mu = (11,659,180.9 +- 7.2[had] +- 3.5[LBL] +- 0.4[QED+EW])e-10 (e+e- -based) and a_mu = (11,659,195.6 +- 5.8[had] +- 3.5[LBL] +- 0.4[QED+EW])e-10 (tau-based), where the errors account for the hadronic, light-by-light (LBL) scattering and electroweak contributions. The deviations from the measurement at BNL are found to be (22.1 +- 7.2 +- 3.5 +- 8.0)e-10 (1.9 sigma) and (7.4 +- 5.8 +- 3.5 +- 8.0)e-10 (0.7 sigma) for the e+e- and tau-based estimates, respectively, where the second error is from the LBL contribution and the third one from the BNL measurement.Comment: 14 pages, 7 figures (to be submitted to Phys Lett B

    Study of e+ee^+e^- collisions with a hard initial state photon at BABAR

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    A study of several 3- and 4-body hadronic final states (π+ππ0,π+ππ+π,K+Kπ+πandK+KK+K\pi^+\pi^-\pi^0, \pi^+\pi^-\pi^+\pi^-, K^+K^-\pi^+\pi^- and K^+K^-K^+K^-) accompanied by a hard photon is presented. These states are produced from e+ee^+e^- collisions at the c.m. energy near the \UPSILON (4S) resonance using a 90fb190 fb^-1 data sample collected with the BABAR detector at the PEP-II collider. The invariant mass of the hadronic final state determines the virtual photon energy, so that the data can be compared with direct e+ee^+e^- cross sections. Cross sections have been obtained from threshold up to 4.5 GeV with systematic errors at the 5% level. The accuracy of the results is comparable with the best direct e+ee^+e^- results overall, but achieves amuch better precision in 1.4-2.5 GeV region where data are sparse. In addition to light meson spectroscopy these data can be used to improve the determination of R -the ratio of e+ee^+e^-\to hadrons cross section to e+eμ+μe^+e^-\to \mu^+\mu^- - and thereby to impact the understanding of the recent (g2)μ(g-2)_\mu  measurement through a better evaluation of the hadronic vacuum polarization contribution. The ISR technique also gives access to J/ψJ/\psi production and allows one to measure branching ratios into 3- and 4-body final states above at a level of precision that is typically better than that obtained in the combined earlier measurements

    Detection of gravitational wave bursts by interferometric detectors

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    We study in this paper some filters for the detection of burst-like signals in the data of interferometric gravitational-wave detectors. We present first two general (non-linear) filters with no {\it a priori} assumption on the waveforms to detect. A third filter, a peak correlator, is also introduced and permits to estimate the gain, when some prior information is known about the waveforms. We use the catalogue of supernova gravitational-wave signals built by Zwerger and M\"uller in order to have a benchmark of the performance of each filter and to compare to the performance of the optimal filter. The three filters could be a part of an on-line triggering in interferometric gravitational-wave detectors, specialised in the selection of burst events.Comment: 15 pages, 8 figure

    Status of the Fermilab Muon (g-2) Experiment

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    The New Muon (g2)(g-2) Collaboration at Fermilab has proposed to measure the anomalous magnetic moment of the muon, aμa_\mu, a factor of four better than was done in E821 at the Brookhaven AGS, which obtained aμ=[116592089(63)]×1011a_\mu = [116 592 089 (63)] \times 10^{-11} ±0.54\pm 0.54 ppm. The last digit of aμa_{\mu} is changed from the published value owing to a new value of the ratio of the muon-to-proton magnetic moment that has become available. At present there appears to be a difference between the Standard-Model value and the measured value, at the 3\simeq 3 standard deviation level when electron-positron annihilation data are used to determine the lowest-order hadronic piece of the Standard Model contribution. The improved experiment, along with further advances in the determination of the hadronic contribution, should clarify this difference. Because of its ability to constrain the interpretation of discoveries made at the LHC, the improved measurement will be of significant value, whatever discoveries may come from the LHC.Comment: Proceedings of the PhiPsi09, Oct. 13-16, 2009, Beijing, China, 4 pages 2 figures. Version 2 includes Fermilab report number, minor corrections and one additional referenc

    Strange Quark Mass from the Invariant Mass Distribution of Cabibbo-Suppressed Tau Decays

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    Quark mass corrections to the tau hadronic width play a significant role only for the strange quark, hence providing a method for determining its mass. The experimental input is the vector plus axial-vector strange spectral function derived from a complete study of tau decays into strange hadronic final states performed by ALEPH. New results on strange decay modes from other experiments are also incorporated. The present analysis determines the strange quark mass at the Mtau mass scale using moments of the spectral function. Justified theoretical constraints are applied to the nonperturbative components and careful attention is paid to the treatment of the perturbative expansions of the moments which exhibit convergence problems. The result obtained, m_s(Mtau^2) = (120 +- 11_exp +- 8_Vus +- 19_th) MeV = (120^+21_-26) MeV, is stable over the scale from Mtau down to about 1.4 GeV. Evolving this result to customary scales yields m_s(1 GeV^2) = (160^+28_-35) MeV and m_s(4 GeV^2) = (116^+20_-25) MeV.Comment: LaTex, 8 pages, 4 figures (EPS
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