Muons against the standard model

Abstract

Physics The standard model (SM) of particle physics has remained frustratingly reliable when tested in experiments. One exception is a 15-year-old measurement of the anomalous magnetic moment of the muon, which shows a discrepancy of 3.7 SDs with respect to the current SM prediction. Abi et al. (the Muon g –2 Collaboration) set out to verify this result using positive muons. Measuring the anomalous precession frequency of the muons in a magnetic field, they indeed found agreement with the previous result. Together, these two measurements deviate even more from the SM prediction, with a combined discrepancy of 4.2 SDs. Future experiments and calculations of the SM prediction will further test the discrepancy and determine what it means for theoretical extensions of the SM. Phys. Rev. Lett. 126 , 141801 (2021).