Anomalous Magnetic Moment of The Muon
The anomalous magnetic moment of the muon is calculated in a similar way; its measurement provides a precision test of the Standard Model. The prediction for the value of the muon anomalous magnetic moment includes three parts: αμSM = αμQED + αμEW + αμhad. The first two components represent the photon and lepton loops, and the W boson and Z boson loops, respectively, and can be calculated precisely from first principles. The third term represents hadron loops, and cannot be calculated accurately from theory alone. It is estimated from experimental measurements of the ratio of hadronic to muonic cross sections (R) in e+e- collisions. As of November 2006, the measurement disagrees with the Standard Model by 3.4 standard deviations, suggesting beyond the Standard Model physics may be having an effect (or theoretical/experimental errors not completely under control).
The E821 experiment at Brookhaven National Laboratory (BNL) studied the precession of muon and anti-muon in a constant external magnetic field as they circulated in a confining storage ring. The E821 Experiment reported the following average value (from the July 2009 review by Particle Data Group)
where the first errors are statistical and the second systematic.
Read more about this topic: Anomalous Magnetic Dipole Moment
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