Muon’s Escalating Challenge to the Standard Model April 7, 2021• Physics 14, 54 Measurements of the muon magnetic moment strengthen a previously reported tension with theoretical predictions, ushering in a new era of precision tests of the standard model. Reidar Hahn/Fermilab g − 2 ring, where the precession of muons in a magnetic field is used to measure the muon magnetic moment. Reidar Hahn/Fermilab g − 2 ring, where the precession of muons in a magnetic field is used to measure the muon magnetic moment.× Twenty years ago, the Brookhaven Muon g − 2 experiment measured a value of the anomalous magnetic moment of the muon that disagreed by several parts per million with calculations based on the standard model (SM) of particle physics [1]. Physicists had long understood that the SM was incomplete, but the Muon