Measurement of the Positive Muon Anomalous Magnetic Moment to 0.20 Ppm

Abstract

We present a new measurement of the positive muon magnetic anomaly, a, equivalent to (g,- 2)/2, from the Fermilab Muon g - 2 Experiment using data collected in 2019 and 2020. We have analyzed more than 4 times the number of positrons from muon decay than in our previous result from 2018 data. The systematic error is reduced by more than a factor of 2 due to better running conditions, a more stable beam, and improved knowledge of the magnetic field weighted by the muon distribution, w similar to ip, and of the anomalous precession frequency corrected for beam dynamics effects, wa. From the ratio wa/w similar to ip, together with precisely determined external parameters, we determine a, = 116 592 057(25) x 10-11 (0.21 ppm). Combining this result with our previous result from the 2018 data, we obtain a,(FNAL) = 116592055(24) x 10-11 (0.20 ppm). The new experimental world average is a,(exp) = 116 592 059(22) x 10-11 (0.19 ppm), which represents a factor of 2 improvement in precision.