Abstract
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^- rightarrow mathrm{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 pm 3.4)times 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 (m_Z^2) is evaluated to be (276.0pm 0.9)times 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
About 73% of the lowest order hadronic contribution and 59% of the total uncertaintysquared are given by the π +π −(γ ) final state,1 while this channel amounts to only 12% of the hadronic contribution to α(s) at s = m2Z
Recent measurements from SND [22] at VEPP-2000 for the K + K − channel agree with BABAR [23], while both show a discrepancy with former SND data, obtained at VEPP-2M below 1.4 GeV, which exceeds the quoted systematic uncertainty
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 energysquared dispersion integrals ranging from the π 0γ threshold to infinity. The kernels occurring in these integrals emphasise low photon virtualities, owing to the 1/s descent of the cross section, and, in the case of aμ, to an additional 1/s suppression In the latter case, about 73% of the lowest order hadronic contribution and 59% of the total uncertaintysquared 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. We reevaluate all the experimental contributions using the software package HVPTools [1], and add to these narrow resonance contributions evaluated analytically and continuum contributions obtained from perturbative QCD
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