New physics in the muon magnetic moment?

Abstract

The muon, a short-lived cousin of the electron, has provided a longstanding discrepancy between the standard model of particle physics and experimental measurements. This suggests that a not-yet-known particle or force perturbs the muon. The discovery of such “new physics” would have profound consequences on our understanding of Nature.In 2021, the attention of the world was drawn to this discrepancy when the announcement of the independent confirmation of the experiment by Fermilab [1] coincided with the publication of our ab-initio calculation (Nature [2]). Our result dramatically updated the theoretical prediction, bringing it significantly closer to the experimental value: it may be possible to explain the Fermilab measurement without any new physics, even with the latest Fermilab update [3]. Our result established a new standard of precision for such calculations that has yet to be challenged; with uncertainties comparable to the experimental measurement and the reference, data-driven computations.We are carrying out new simulations to reduce both the systematic and statistical uncertainties. Both improvements are required in order to match the precision of the final Fermilab measurement, to be obtained in the coming years. As such, these simulations will be critical to determine whether the muon's magnetic moment harbours new fundamental physics.