Abstract
An update of the hadronic vacuum polarisation contributions to the muon magnetic anomaly and to the running of the electromagnetic couplings constant at the Z-boson mass is presented. Newest e+e−→ hadrons cross-section data mainly from the BABAR and VEPP-2000 experiments have been included. For the muon (g−2)/2, the lowest-order hadronic contribution is evaluated to be (693.1 ± 3.4) · 10−10, improving the precision of our previous evaluation by 21%. The full Standard Model prediction differs by 3.5 σ from the experimental value. The five-quark hadronic contribution to $ \alpha (\mathop m\nolimits_z^2 ) $ is evaluated to be (276.0 ± 0.9) · 10−4.
Highlights
The Standard Model (SM) predictions of the anomalous magnetic moment of the muon, aμ =/2, with gμ the muon gyromagnetic factor, and of the running electromagnetic coupling constant, α(s), a crucial ingredient of electroweak theory, are limited in precision by hadronic vacuum polarisation (HVP) contributions
The dominant hadronic terms can be calculated with a combination of experimental cross-section data, involving e+e− annihilation to hadrons, and perturbative QCD
About 74% of the lowest order hadronic contribution and 59% of the total uncertainty-squared are given by the π+π−(γ) final state, while this channel amounts to only 12% of the hadronic contribution to α(s) at s = m2Z
Summary
The dominant hadronic terms can be calculated with a combination of experimental cross-section data, involving e+e− annihilation to hadrons, and perturbative QCD. They are used to evaluate energy-squared dispersion integrals ranging from the π0γ threshold to infinity. The kernels occurring in these integrals emphasise low photon virtuality, owing to the 1/s descent of the cross-section, and, in case of aμ, to an additional 1/s suppression In the latter case, about 74% of the lowest order hadronic contribution and 59% of the total uncertainty-squared are given by the π+π−(γ) final state, while this channel amounts to only 12% of the hadronic contribution to α(s) at s = m2Z. In this proceedings in common with that of EPS 2017, we report an update, detailed in Ref. [1], of the lowest-order hadronic contribution, ahμad,LO, to the muon magnetic anomaly, and the hadronic contribution, ∆αhad(m2Z), to α(s) at the Z-boson mass using newest e+e− → hadrons cross-section data
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