Determining the Electron's Magnetic Strength to Test the Laws of Physics

Following up on 2021 results, in August 2023 Fermilab released a further update of the muon anomalous magnetic moment (g−2). The new value is consistent with the 2006 Brookhaven measurement and reduces the uncertainty to 0.20 ppm. While it differs from the Standard Model theoretical consensus by more than 5σ, this does not immediately indicate new physics: hadronic contributions have seen major developments that leave the theoretical value itself in flux. For the electron — the lightest charged lepton — g−2 was newly measured in 2021 to a precision of 0.12 ppb. To obtain a theoretical value at matching precision, the fine-structure constant α is needed at comparable accuracy; values at 0.20 ppb (2018) and 0.081 ppb (2020) have been obtained, raising the possibility of probing new physics with electron g−2 as well. This talk reviews the status of precision tests with lepton g−2, and describes our work and outlook in the quantum electrodynamics (QED) calculations that make these tests possible.