More Evidence That There Is No Muon g-2 Anomaly

Once again, it has become clear that the "data driven" means of estimating the Standard Model prediction for the anomalous magnetic moment of the muon was flawed and the the experimental result is actually consistent with the Standard Model prediction in a very global tests of the completeness and correctness of the Standard Model at high precision that strongly disfavors a variety of new physics models.

An accurate calculation of the leading-order hadronic vacuum polarisation (LOHVP) contribution to the anomalous magnetic moment of the muon (aμ) is key to determining whether a discrepancy, suggesting new physics, exists between the Standard Model and experimental results. 

This calculation can be expressed as an integral over Euclidean time of a current-current correlator G(t), where G(t) can be calculated using lattice QCD or, with dispersion relations, from experimental data for e+e−→hadrons. The BMW/DMZ collaboration recently presented a hybrid approach in which G(t) is calculated using lattice QCD for most of the contributing t range, but using experimental data for the largest t (lowest energy) region. Here we study the advantages of varying the position t=t1 separating lattice QCD from data-driven contributions. The total LOHVP contribution should be independent of t1, providing both a test of the experimental input and the robustness of the hybrid approach. 

We use this criterion and a correlated fit to show that Fermilab/HPQCD/MILC lattice QCD results from 2019 strongly favour the CMD-3 cross-section data for e+e−→π+π− over a combination of earlier experimental results for this channel. 

Further, the resulting total LOHVP contribution obtained is consistent with the result obtained by BMW/DMZ, and supports the scenario in which there is no significant discrepancy between the experimental value for aμ and that expected in the Standard Model. 

We then discuss how improved lattice results in this hybrid approach could provide a more accurate total LOHVP across a wider range of t1 values with an uncertainty that is smaller than that from either lattice QCD or data-driven approaches on their own.

C. T. H. Davies, et al., "Utility of a hybrid approach to the hadronic vacuum polarisation contribution to the muon anomalous magnetic moment" arXiv:2410.23832 (October 31, 2024).