A groundbreaking high-precision calculation concerning the magnetic moment of the muon, the electron’s heavier counterpart, has resulted in a rare alignment between theoretical predictions and experimental results. This advancement reinforces the Standard Model, casting doubt on the prospects for new physics.
Muon particles traversing lead in a cloud chamber. Image credit: Jino John 1996 / CC BY-SA 4.0.
Muons are subatomic particles that resemble electrons but are roughly 200 times more massive.
These particles are generated when cosmic rays collide with the Earth’s atmosphere, with approximately 50 muons passing through the human body every second.
Like electrons, muons exhibit magnetic properties, operating as tiny magnets. This magnetic strength, known as magnetic moment, has long been a critical tool for testing the Standard Model, a theoretical framework that elucidates the fundamental particles and forces of nature.
“Muons are short-lived elementary particles with half the spin and 207 times the mass of an electron,” explained Finn Stokes, a physicist at the University of Adelaide.
“Both particles generate a magnetic field characterized by a magnetic dipole moment.”
“This moment is proportional to the particle’s spin and charge, and inversely related to twice its mass.”
For years, discrepancies between the theoretical and experimental strengths of muon magnetism hinted at the potential for new physics beyond the Standard Model.
However, recent research by a dedicated team has resolved this contradiction, reinforcing the Standard Model instead of challenging it.
“Our research delves into the most uncertain aspect of theoretical predictions: the contribution of hadronic vacuum polarization arising from the complex dynamics of quarks and gluons shaped by quantum chromodynamics (QCD),” Dr. Stokes noted.
“Calculating the effects of these strong forces with high precision has proven to be challenging.”
“To overcome this hurdle, we employed a novel hybrid approach, merging large-scale computer simulations with experimental data.”
Utilizing the world’s most advanced supercomputers and a method known as lattice QCD, the researchers achieved calculations at unprecedented resolutions, effectively reducing uncertainties.
This new result is nearly twice as accurate as the previous global consensus.
They have calculated the contribution of hadronic vacuum polarization with unmatched precision, leading to an updated prediction of the muon’s magnetic moment in alignment with the latest experimental measurements, agreeing to within just 0.5 standard deviations.
“This study highlights the synergistic power of integrating theoretical and experimental methodologies to address some of the most intricate challenges in physics,” stated Dr. Stokes.
“This significant advancement enhances our capacity to rigorously test the Standard Model. Such a reduction in uncertainty facilitates unprecedented comparisons between theory and experiment, leading to remarkable validation of the Standard Model to 11 decimal places.”
For more details, check the results published on April 22, 2026, in the journal Nature.
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A. Bocaretti et al. Hybrid calculation of hadronic vacuum polarization in muon g – 2 to 0.48%. Nature published online on April 22, 2026. doi: 10.1038/s41586-026-10449-z
Source: www.sci.news
