Measurement of the Electron Magnetic Moment

The electron magnetic moment, -μ/μB=g/2=1.001 159 652 180 59 (13) [0.13 ppt], is determined 2.2 times more accurately than the value that stood for fourteen years. The most precisely determined property of an elementary particle tests the most precise prediction of the standard model (SM) to 1 part in 1012. The test would improve an order of magnitude if the uncertainty from discrepant measurements of the fine structure constant α is eliminated since the SM prediction is a function of α. The new measurement and SM theory together predict α-1=137.035 999 166 (15) [0.11 ppb] with an uncertainty 10 times smaller than the current disagreement between measured α values.