The $g-2$ of charged leptons, $\alpha(M_Z^2)$ and the hyperfine splitting of muonium

TL;DR

This paper updates the calculations of hadronic contributions to the anomalous magnetic moments of leptons, muonium hyperfine splitting, and the running of the QED coupling, revealing a 3.8 sigma discrepancy in muon g-2.

Contribution

It provides revised evaluations of hadronic vacuum polarization effects and their impact on fundamental lepton properties and the QED coupling at the Z boson scale.

Findings

Updated hadronic vacuum polarization contributions to lepton g-2 and muonium hyperfine splitting.

The muon g-2 discrepancy is now 3.8 sigma from the Standard Model.

Refined estimates of the hadronic effects on the running of the QED coupling.

Abstract

Following updates in the compilation of $e^+e^-\rightarrow{\rm hadrons}$ data, this work presents re-evaluations of the hadronic vacuum polarisation contributions to the anomalous magnetic moment of the electron ($a_e$), muon ($a_\mu$) and tau lepton ($a_\tau$), to the ground-state hyperfine splitting of muonium and also updates the hadronic contributions to the running of the QED coupling at the mass scale of the $Z$ boson, $\alpha(M_Z^2)$. Combining the results for the hadronic vacuum polarisation contributions with recent updates for the hadronic light-by-light corrections, the electromagnetic and the weak contributions, the deviation between the measured value of $a_\mu$ and its Standard Model prediction amounts to $\Delta a_{\mu} = (28.02 \pm 7.37) \times 10^{-10}$, corresponding to a muon $g-2$ discrepancy of $3.8\sigma$.