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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_μ ≡ (g_μ − 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_p', and of the anomalous precession frequency corrected for beam dynamics effects, ω_a. From the ratio ω_a /ω_p', together with precisely determined external parameters, we determine a_μ = 116 592 057(25) × 10⁻¹¹ (0.21 ppm). Combining this result with our previous result from the 2018 data, we obtain a_μ (FNAL) = 116 592 055(24) × 10⁻¹¹ (0.20 ppm). The new experimental world average is a_μ (exp) = 116 592 059(22) × 10⁻¹¹ (0.19 ppm), which represents a factor of 2 improvement in precision.

Muon g-2 Collaboration, Physical Review Letters, 131 (2023) 161802. DOI: 10.1103/PhysRevLett.131.161802

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