New Measurement of the Electron Magnetic Moment and the Fine Structure Constant
Prof. Dr. Gerald Gabrielse (Department of Physics, Harvard University)

A measurement using a one-electron quantum cyclotron gives the electron magnetic moment in Bohr magnetons, g/2 = 1.001 159 652 180 73 (28) [0.28 ppt], with an uncertainty 2.7 and 15 times smaller than for previous measurements in 2006 and 1987. The electron is used as a magnetometer to allow line shape statistics to accumulate, and its spontaneous emission rate determines the correction for its interaction with a cylindrical trap cavity.

With quantum electrodynamics (QED) and the assumption of no new physics beyond the standard model of particle physics, the new measurement determines the fine structure constant alpha 20 times more accurately than any independent method. The measured g/2 is accurate enough to allow testing QED, probing for electron size, and searching for a low-mass dark-matter particle if a more accurate independent measurement of alpha is realized.