Direct Measurement of the Proton Magnetic Moment

The proton magnetic moment in nuclear magnetons is measured to be ${\mu }_p\mathrm{/}{\mu }_N\equiv g\mathrm{/}2=2.792846\pm 0.000007$, a 2.5 ppm (parts per million) uncertainty. The direct determination, using a single proton in a Penning trap, demonstrates the first method that should work as well with an antiproton as with a proton. This opens the way to measuring the antiproton magnetic moment (whose uncertainty has essentially not been reduced for 20 years) at least ${10}^3$ times more precisely.