Abstract
We present the first results of the Fermilab National Accelerator Laboratory (FNAL) Muon Experiment for the positive muon magnetic anomaly . The anomaly is determined from the precision measurements of two angular frequencies. Intensity variation of high-energy positrons from muon decays directly encodes the difference frequency between the spin-precession and cyclotron frequencies for polarized muons in a magnetic storage ring. The storage ring magnetic field is measured using nuclear magnetic resonance probes calibrated in terms of the equivalent proton spin precession frequency in a spherical water sample at . The ratio , together with known fundamental constants, determines (0.46 ppm). The result is 3.3 standard deviations greater than the standard model prediction and is in excellent agreement with the previous Brookhaven National Laboratory (BNL) E821 measurement. After combination with previous measurements of both and , the new experimental average of (0.35 ppm) increases the tension between experiment and theory to 4.2 standard deviations.
- Received 14 March 2021
- Accepted 25 March 2021
- Corrected 7 May 2021
DOI:https://doi.org/10.1103/PhysRevLett.126.141801
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Corrections
7 May 2021
Correction: Missing information in Ref. [60] has been inserted.
Viewpoint
Muon’s Escalating Challenge to the Standard Model
Published 7 April 2021
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.
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