Measurement of the Electron Magnetic Moment

Understand

The electron magnetic moment,$-\mu/\mu_B = g/2 = 1.001 \, 159 \, 652 \, 180 \, 59 \, (13) \, [0.13\, \rm{ppt}]$, is determined 2.2 times more accurately than the value that stood for 14 years.

• The most precisely determined property of an elementary particle tests the most precise prediction of the Standard Model (SM) to $1$ part in $10^{12}$.
• The test would improve an order of magnitude if the uncertainty from discrepant measurements of the fine structure constant $\alpha$ is eliminated since the SM prediction is a function of $\alpha$.
• The new measurement and SM theory together predict $\alpha^{-1}=137.035 \, 999 \, 166 \, (15) \, [0.11 \, \rm{ppb}]$ with an uncertainty ten times smaller than the current disagreement between measured $\alpha$ values.