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Register a new userReevaluation of the hadronic vacuum polarisation contributions to the Standard Model predictions of the muon g-2 and alpha(mZ) using newest hadronic cross-section data
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We reevaluate the hadronic vacuum polarisation contributions to the muon magnetic anomaly and to the running of the electromagnetic coupling constant at the Z-boson mass. We include newest e+e- to hadrons cross-section data (among others) from the BABAR and VEPP-2000 experiments. For the muon (g-2)/2 we find for the lowest-order hadronic contribution (693.1 +- 3.4) 10^-10, improving the precision of our previous evaluation by 21%. The full Standard Model prediction differs by 3.5 sigma from the experimental value. The five-quark hadronic contribution to alpha(mZ) is evaluated to be (276.0 +- 0.9) 10^-4.
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We reevaluate the hadronic contributions to the muon magnetic anomaly, and to the running of the electromagnetic coupling constant at the Z-boson mass. We include new pi+pi- cross-section data from KLOE, all available multi-hadron data from BABAR, a reestimation of missing low-energy contributions using results on cross sections and process dynamics from BABAR, a reevaluation of all experimental contributions using the software package HVPTools, together with a reanalysis of inter-experiment and inter-channel correlations, and a reevaluation of the continuum contributions from perturbative QCD at four loops. These improvements lead to a decrease in the hadronic contributions with respect to earlier evaluations. For the muon g-2 we find lowest-order hadronic contributions of (692.3 +- 4.2) 10^-10 and (701.5 +- 4.7) 10^-10 for the e+e- based and tau-based analyses, respectively, and full Standard Model predictions that differ by 3.6 sigma and 2.4 sigma from the experimental value. For the e+e- based five-quark hadronic contribution to alpha(MZ) we find Delta_alpha_had[5](MZ)=(275.7 +- 1.0) 10^-4. The reduced electromagnetic coupling strength at MZ leads to an increase by 7 GeV in the most probable Higgs boson mass obtained by the standard Gfitter fit to electroweak precision data.
Precise data on e^+e^- to hadrons have recently become available and are used to compute the lowest-order hadronic vacuum polarisation contribution to the muon magnetic anomaly through dispersion relations. This is the case for the dominant pi+ pi- channel, but the most significant progress comes from the near completion of the BABAR program of measuring exclusive processes below 2 GeV with the initial-state radiation method which allows an efficient coverage of a large range of energies.. In this paper we briefly review the data treatment, the achieved improvements, and the result obtained for the full Standard Model prediction of the muon magnetic anomaly. The value obtained, a_mu (had~LO)=(692.6 +- 3.3)x 10^{-10} is 20% more precise than our last estimate in 2010. It deviates from the direct experimental determination by (27.4 +- 7.6)x 10^{-10} (3.6 sigma). Perpectives for further improvement are discussed.
We reanalyze the two-loop electroweak hadronic contributions to the muon g-2 that may be enhanced by large logarithms. The present evaluation is improved over those already existing in the literature by the implementation of the current algebra Ward identities and the inclusion of the correct short-distance QCD behaviour of the relevant hadronic Greens function.
We compute the vacuum polarisation on the lattice in quenched QCD using non-perturbatively improved Wilson fermions. Above Q^2 of about 2 GeV^2 the results are very close to the predictions of perturbative QCD. Below this scale we see signs of non-perturbative effects which we can describe by the use of dispersion relations. We use our results to estimate the light quark contribution to the muons anomalous magnetic moment. We find the result 446(23) x 10^{-10}, where the error only includes statistical uncertainties. Finally we make some comments on the applicability of the Operator Product Expansion to our data.
Results on the lowest-order hadronic vacuum polarization contribution to the muon magnetic anomaly are presented. They are based on the latest published experimental data used as input to the dispersion integral. Thus recent results on tau to nutau pi pi0 decays from Belle and on e+ e- annihilation to pi+ pi- from BABAR and KLOE are included. The new data, together with improved isospin-breaking corrections for tau decays, result into a much better consistency among the different results. A discrepancy between the Standard Model prediction and the direct g-2 measurement is found at the level of 3 sigma.
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