A new high-precision calculation of a key component underpinning the magnetic moment of the muon, a heavier cousin of the electron, brings theory and experiment into rare alignment, reinforcing the Standard Model and dimming hopes of new physics.
A muon particle passing through lead in a cloud chamber. Image credit: Jino John 1996 / CC BY-SA 4.0.
The muon is a subatomic particle similar to an electron but around 200 times heavier.
Muons are produced when cosmic rays hit Earth’s atmosphere. Roughly 50 of these muons pass through the human body every second.
Like the electron, the muon behaves as a tiny magnet. The strength of this magnetism (its magnetic moment) has long served as a powerful test of the Standard Model, the theory describing the fundamental particles and forces of nature.
“The muon is a short-lived elementary particle with spin 1/2 and a mass 207 times larger than that of the electron,” said Adelaide University physicist Finn Stokes and his colleagues.
“Both particles create a magnetic field around them, characterized by a magnetic dipole moment.”
“This moment is proportional to the spin and charge of the particle and inversely proportional to twice its mass.”
For years, the strength of the muon’s magnetism has exhibited a persistent discrepancy between theory and experiment, hinting at the possibility of undiscovered physics beyond the Standard Model.
However, the team’s new study finally resolves this discrepancy, reinforcing this model, rather than breaking it.
“Our research focuses on the most uncertain part of the theoretical prediction: the hadronic vacuum polarization contribution, which arises from the complex interactions of quarks and gluons governed by quantum chromodynamics (QCD),” Dr. Stokes said.
“These strong-force effects are really difficult to calculate with high precision.”
“To overcome this challenge, we used a novel hybrid approach that combines large-scale computer simulations with experimental data.”
Using some of the world’s most powerful supercomputers and a technique known as lattice QCD, the researchers performed calculations at a higher resolution than ever before, allowing them to significantly reduce uncertainties.
The result is almost twice as precise as the previous worldwide consensus.
They determined the hadronic vacuum polarization contribution with unprecedented accuracy, leading to a new Standard Model prediction for the muon’s magnetic moment.
This updated prediction agrees with the latest experimental measurements to within just 0.5 standard deviations.
“The work demonstrates the power of combining theoretical and experimental techniques to tackle some of the most challenging problems in physics,” Dr. Stokes said.
“This is a major step forward in our ability to test the Standard Model. With this reduction in uncertainties, we can now compare theory and experiment with unprecedented precision, providing a remarkable validation of the Standard Model to 11 decimal places.”
The results were published on April 22, 2026 in the journal Nature.
_____
A. Boccaletti et al. Hybrid calculation of hadronic vacuum polarization in muon g – 2 to 0.48%. Nature, published online April 22, 2026; doi: 10.1038/s41586-026-10449-z
