One-Particle Measurement of the Antiproton Magnetic Moment

The antiproton $(\bar{p})$ magnetic moment $\mu \bar{p} = \mu_{\bar{p}} S/(\bar{h}/2)$ is proportional to its spin $S$. A single trapped $\bar{p}$ is used for the first time to measure the $\bar{p}$ magnetic moment in nuclear magnetons, giving $\mu_\bar{p}/\mu N = -2.792 845 \pm 0.000 012$. The 4.4 parts per million (ppm) uncertainty is 680 times smaller than previously realized. Comparing to the proton moment $\mu_{p} = \mu_{p} S/\bar{h}/2)$ measured using the same method and trap electrodes gives $\mu_{\bar{p}}/\mu_{p} = -1.000 000 \pm 0.000 005$ to 5 ppm, consistent with the prediction of the CPT theorem.