Precision measurement of the muon magnetic moment (g-2)
Medida de precisión del momento magnético del muon (g-2)
- Date
- 2021-2025 · confidence high
- Place
- Fermilab, Batavia, Illinois, United States
- Credited to
- Muon g-2 Collaboration (Fermilab); Brookhaven E821
- Field
- Cosmos & Earth
⚠️ Disputed: the sources disagree.
What was discovered
Fermilab confirms in 2021 and refines in 2023-2025 the measurement of the muon's anomalous magnetic moment with a precision of 0.2 parts per million; the 4.2-sigma discrepancy with the standard model seen in 2021 was diluted once lattice QCD calculations revised the theoretical prediction. It is the most demanding precision test of the standard model.
The status of the 'anomaly' is controversial: it depends on whether the theoretical prediction uses e+e- data or lattice calculations; Fermilab's final result (2025) is compatible with the lattice.
What it led to
- Precision tests of physics beyond the standard model
- Lattice QCD calculations of hadronic vacuum polarisation
- J-PARC g-2 experiment
Built on
- Quantum electrodynamics (QED)1947-1949
- Lamb shift and the electron g-2
- Brookhaven E821 experiment (2001-2006)
Made possible
- High-precision muon storage rings