Abstract
Hadronic vacuum polarization (HVP) is not only a critical part of the standard model (SM) prediction for the anomalous magnetic moment of the muon (g-2)_{μ}, but also a crucial ingredient for global fits to electroweak (EW) precision observables due to its contribution to the running of the fine-structure constant encoded in Δα_{had}^{(5)}. We find that with modern EW precision data, including the measurement of the Higgs mass, the global fit alone provides a competitive, independent determination of Δα_{had}^{(5)}|_{EW}=270.2(3.0)×10^{-4}. This value actually lies below the range derived from e^{+}e^{-}→hadrons cross section data, and thus goes into the opposite direction as would be required if a change in HVP were to bring the SM prediction for (g-2)_{μ} into agreement with the Brookhaven measurement. Depending on the energy where the bulk of the changes in the cross section occurs, reconciling experiment and SM predictions for (g-2)_{μ} by adjusting HVP would thus not necessarily weaken the case for physics beyond the SM (BSM), but to some extent shift it from (g-2)_{μ} to the EW fit. We briefly explore some options of BSM scenarios that could conceivably explain the ensuing tension.
Highlights
Introduction.—The standard model (SM) of particle physics has been established with increasing precision over the last decades
Depending on the energy where the bulk of the changes in the cross section occurs, reconciling experiment and SM predictions for ðg − 2Þμ by adjusting Hadronic vacuum polarization (HVP) would not necessarily weaken the case for physics beyond the SM (BSM), but to some extent shift it from ðg − 2Þμ to the EW fit
Global analyses based on a direct integration of cross section data [25,26,29,30] can be combined with analyticity and unitarity constraints for the leading 2π [27,29,53] and 3π [28] channels, covering almost 80% of the HVP contribution, to demonstrate that the experimental data sets are consistent with general properties of QCD, and radiative corrections for the 2π channel have been completed at next-to-leading order [54]
Summary
Introduction.—The standard model (SM) of particle physics has been established with increasing precision over the last decades. In scenario (1) we find consistency between the value from eþe− data and the other observables of the global fit, as can be seen from the good agreement between the measurement and the posterior of Δαðh5aÞd.
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