Direct Measurement of the Proton Magnetic Moment

The proton magnetic moment in nuclear magnetons is measured to be μ_p/μ_N≡g/2=2.792846±0.000007, a 2.5 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 (p¯) as with a proton (p). This opens the way to measuring the p¯ magnetic moment (whose uncertainty has essentially not been reduced for 20 years) at least 10³ times more precisely.