Measurement of the Positive Muon Anomalous Magnetic Moment to 0.20 ppm

We present a new measurement of the positive muon magnetic anomaly, aμ≡(gμ-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, ω[over ˜]ₚ', and of the anomalous precession frequency corrected for beam dynamics effects, ωₐ. From the ratio ωₐ/ω[over ˜]ₚ', together with precisely determined external parameters, we determine aμ=116 592 057(25)×10⁻¹¹ (0.21 ppm). Combining this result with our previous result from the 2018 data, we obtain aμ(FNAL)=116 592 055(24)×10⁻¹¹ (0.20 ppm). The new experimental world average is aμ(exp)=116 592 059(22)×10⁻¹¹ (0.19 ppm), which represents a factor of 2 improvement in precision.