Standard Model Muon g-2 Calculation Closely Matches Experimental Data

The most accurate ever calculation of the Standard Model predicted value of muon g-2 matches the world average experimentally measured value to 0.7 sigma (with the prediction and the experimental measurement having a precision of 310 and 124 parts per billion, respectively).

The new theoretically calculated value for muon g-2 is: 

aμ = (116,592,052 ± 36) × 10−11.

The most precise available experimental measurement is as follows:

Fermilab (2025): (116,592,070.5 ± 14.8) × 10−11.

The difference is (18.5 ± 38.9) × 10−11

The relative experimental result has an uncertainty of 0.127 ppm. The new calculation of the Standard Model expected value has a relative uncertainty of 0.31 ppm.

The error weighted experimental world average, which has a relative uncertainty of 0.124 ppm is: 

(116,592,071.5 ± 14.5) × 10−11. 

This final result is recapped in an exhaustive final muon g-2 experimental data report at arXiv:2606.17323.

The difference between the world average and the new SM prediction calculation is 

(28.5 ± 38.8) × 10−11, which is 0.7 sigma (which is still closer than than one sigma expected by a random distribution of uncertainties if the results are identical).

This global test of the Standard Model (which implicates all three of its forces) at low energies passes with flying colors.

For 50 years, the standard model of particle physics has been very successful in describing subatomic phenomena. In the past quarter of a century, this was challenged by a mismatch between its predictions and precision measurements of the anomalous magnetic moment of the muon, a(μ). This disagreement was eventually reconciled, first through a determination in an ab initio lattice calculation of the most uncertain theoretical contribution, the leading-order hadronic vacuum polarization (LO-HVP), a(μ)^(LO-HVP) and subsequently by experimental results and updates of the reference standard-model predictions using lattice results for a(μ)^(LO-HVP).

Here we present a new calculation for this crucial quantity, obtaining 

. This reduces the uncertainty by a factor of 1.6 compared with our earlier computation. We use a hybrid approach that includes a small, long-distance contribution from experiments in a low-energy regime in which they all agree. Our approach combines the strengths of experimental and lattice data in different energy ranges, achieving better precision than with either alone. Our lattice quantum chromodynamics (QCD) simulations are performed on finer lattices . . . allowing for an even more accurate continuum extrapolation. 

Combined with the calculations of the other standard-model contributions . . . our result leads to a prediction that differs from the recent measurement of a(μ) by only 0.5 standard deviations. This provides a notable validation of the standard model to 11 digits.

A. Boccaletti, et al., "Hybrid calculation of hadronic vacuum polarization in muon g − 2 to 0.48%." 653 (8814) Nature 373 (April 22, 2026) (open access) DOI: 10.1038/s41586-026-10449-z

While the hadronic part of the calculation accounts for a fairly modest part of the total value, it is the source of almost all of the uncertainty in the calculation: