First Single Particle Measurements of the Proton and Antiproton Magnetic Moments

Abstract

We report a new comparison of the proton (p) and antiproton ((\bar{p})) magnetic moments. In nuclear magnetons, (\mu_p/\mu_N) = 2.792 846 (7) [2.5 ppm], while (\mu_{\bar{p}}/\mu_N) = 2.792 845 (12) [4.4 ppm]. The unprecedented accuracy of the antiproton measurement is 680 times more precise than previous work. These first single-particle measurements provide a stringent test of CPT invariance. Our comparison, (\mu_{\bar{p}}/\mu_p) = -1.000 000 (5) [5.0 ppm], is consistent with the prediction of the CPT theorem. We also report the observation of a single proton spin flip, opening a path to improved precision by an additional factor of (10^3) or (10^4).