Muon g−2 Experiment

Precision measurement of the muon magnetic anomaly, testing quantum corrections from every known field.

Muons circulate in a 15-metre storage ring at the "magic momentum" where electric fields drop out of the spin precession.
Fermilab’s final 2025 result pinned the anomaly to 127 parts per billion.
Comparison with the Standard Model now hinges on hadronic vacuum-polarization calculations, where lattice QCD shifted the picture.