Improved determination of α(MZ2) and the anomalous magnetic moment of the muon

We reevaluate the hadronic contribution to the running of the QED fine structure constant α(s) at s=MZ2. We use data from e+e− annihilation and τ decays at low energy and at the qq̄ thresholds, where resonances occur. Using so-called spectral moments and the Operator Product Expansion (OPE), it is shown that a reliable theoretical prediction of the hadronic production rate R(s) is available at relatively low energies. Its application improves significantly the precision on the hadronic vacuum polarization contribution. We obtain Δαhad(MZ2)=(277.8±2.6)×10−4 yielding α−1(MZ2)=128.923±0.036. Inserting this value in a global electroweak fit using current experimental input, we constrain the mass of the Standard Model Higgs boson to be MHiggs=129+103−62 GeV. Analogously, we improve the precision of the hadronic contribution to the anomalous magnetic moment of the muon for which we obtain aμhad=(695.1±7.5)×10−10.