Is new physics lurking in the magnetic interaction of a muon?

Is new physics lurking in the magnetic interaction of a muon?

The interaction of a muon’s spin with a magnetic field defines its magnetic moment in terms of the gyromagnetic ratio, g. In the Dirac equation, g is exactly 2, but additional higher order QED, electroweak and strong interactions increase its value by ~ 0.1% such that g-2 is predicted to be: 0.0023318362(9). g of the electron is the most accurately predicted and measured quantity in physics and g of the muon is the most accurately measured quantity using a particle accelerator storage ring. 

At present there exists a discrepancy between the measurement of the muon’s g-2 (0.0023318412(8)) and the prediction with a significance of 4.2 standard deviations mirroring other anomalies seen in decays of b-quarks to muons. Whether this is telling us that there is new physics beyond the Standard Model of particle physics e.g., that could explain the preponderance of dark-matter in the universe, or a statistical fluctuation will likely be resolved by the next round of measurements from the Fermilab Muon g-2 experiment in the USA. I will describe the recent, world's best, measurement from this experiment and the plans to achieve its ultimate precision of 0.14 parts per million and so hopefully resolve whether the magnetic interaction of a muon is a harbinger of new physics.

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