The Muon as a Window to New Physics

The muon g-2 experiment, which started running at Fermilab, uses muons as a window to search for new physics. The Fermilab experiment aims to measure the magnetic moment of the muon with exquisite precision reducing the already very small uncertainties of previous measurements by over a factor of four. It turns out that the muon’s magnetic moment is sensitive to the presence of new (as yet unknown) particles through their virtual effects. But the muon’s magnetic moment also receives contributions from virtual effects of all known particles. These effects are predicted, in principle, within the Standard Model of particle physics. However, the contributions from particles that experience the strong interactions (hadronic corrections) are very challenging to calculate and are therefore the dominant source of theory error. Hence, in order to use the Fermilab experiment to discover new physics, these theoretical uncertainties must be reduced to match the target precision.

During her CAS appointment, Professor El-Khadra will refine her collaboration’s calculation of the hadronic corrections to include missing contributions, which will produce theoretical predictions with significantly reduced uncertainties. She will also organize a workshop of the Muon g-2 Theory Initiative in September of 2019. The initiative, which she chairs, includes over 60 researchers from three continents, and brings together the different communities that are engaged in theoretical calculations of the muon magnetic moment, to enhance and coordinate the individual efforts, inspire new efforts, and provide updates and summarizes of the theory status.