Hadronic Vacuum Polarization: (g-2)μ versus Global Electroweak Fits

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 Δαhad(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 Δαhad(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.