The muon magnetic moment (g−2), final measurement
Muon g-2 Collaboration (Fermilab)
This page delivers no verdict; it presents claims and evidence with their sources. No theory in science is absolute. Method
For everyone
The muon's magnetic property is a very sensitive test of the Standard Model. For years the experimental value and the theoretical prediction seemed to disagree, which was discussed as a sign of "new physics". Fermilab's final result in June 2025 reached a precision of 127 parts per billion. Its gap with the theoretical prediction, updated at the same time, largely closed.
For specialists
The experiment found a_μ = 116 592 070 5(148) × 10⁻¹² (127 ppb); the new world average is 116 592 071 5(145) × 10⁻¹². The 2020 Theory Initiative prediction computed hadronic vacuum polarisation from e⁺e⁻ → hadrons data and gave a discrepancy of about 5σ. The 2025 update relies on lattice QCD and agrees with experiment. The tension between data-driven and lattice-based calculations is itself an open question.
Claims
- The muon anomalous magnetic moment has been measured to 127 ppb.[1]
Evidence
Supporting
The 2020–2023 data agreed with the previously published 2021 and 2023 results and were combined.[1]
Challenging
—
Open questions
- Why do data-driven and lattice-QCD calculations of the hadronic contribution disagree?
Connections
Sources
- Article (2025). Measurement of the positive muon anomalous magnetic moment to 127 ppb. Physical Review Letters 135, 101802arXiv:2506.03069archive
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Cite this page
Athena contributors. (2026). The muon magnetic moment (g−2), final measurement. Athena: The tree of human knowledge. Retrieved November 1, 2026, from https://latifkedi.github.io/athena/en/d/muon-g2/
@misc{athena_muon_g2,
title = {The muon magnetic moment (g−2), final measurement},
author = {{Athena contributors}},
year = {2026},
howpublished = {\url{https://latifkedi.github.io/athena/en/d/muon-g2/}},
note = {Athena: The tree of human knowledge. Accessed: 2026-11-01}
}Added: September 27, 2026 · Last changed: September 27, 2026 · Page history