Update of g-2 of the muon and Delta alpha

TL;DR

The paper revises the Standard Model prediction for the muon anomalous magnetic moment and the hadronic contributions to the running QED coupling by incorporating new hadronic cross-section data, especially in the $2\pi$ channel and the energy region below $2\,\mathrm{GeV}$. It utilizes dispersion relations with $e^+e^-\to$ hadrons data, including recent CMD-2, SND, KLOE, and BaBar measurements, and performs a sum-rule analysis to reconcile inclusive and exclusive data with perturbative QCD expectations. The updated results yield $a_{c mu}^{\rm SM}=(116\,591\,773\pm48)\cdot10^{-11}$ and a $a_{c mu}^{\rm EXP}-a_{c mu}^{\rm SM}=(31.6\pm7.9)\cdot10^{-10}$ discrepancy, about $4\sigma$, when using $e^+e^-$ data; the hadronic contribution uncertainties remain a key factor for precision and future improvements are anticipated from ongoing and upcoming experiments. The work also provides a refined value for $\Delta\alpha^{(5)}_{\rm had}(M_Z^2)=0.02760\pm0.00015$, improving constraints in electroweak fits and influencing Higgs mass inferences.

Abstract

We update our Standard Model predictions for g-2 of the muon and for the hadronic contributions to the running of the QED coupling, Delta alpha^5_had(M_Z^2). Particular emphasis is put on recent changes in the hadronic contributions from new data in the 2pi channel and from the energy region just below 2 GeV.