▪ Abstract 

The E821 Experiment at the Brookhaven Alternating Gradient Synchrotron has measured the muon anomalous magnetic moment to a relative precision of 0.5 parts per million. This effort required a new beamline, a super-ferric muon storage ring with a highly uniform magnetic field, a precision magnetic field measurement system, and electromagnetic calorimeters to record the electrons from muon decay, which carry the essential spin precession frequency information. Data obtained over five years resulted in more than nine billion analyzed events, in nearly equal samples of both muon charges. The experimental results + = 11 659 203(8) × 10−10 and = 11 659 214(9) × 10−10 are consistent with each other, as predicted by the invariance theorem. The combined result ± = 11 659 208(6) × 10−10 is 0.9–2.4 standard deviations higher than predicted by theory; the range depends on the method employed to obtain the hadronic vacuum polarization term in the standard-model calculation. We review the experimental design, physical realization, and analysis procedures and compare the results to the theoretical prediction.


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  • Article Type: Review Article
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