One-Particle Measurement of the Antiproton Magnetic Moment

Abstract

For the first time a single trapped antiproton ($\overline{p}$) is used to measure the $\overline{p}$ magnetic moment ${\mathbit{$\mu${}}}_{\overline{p}}$. The moment ${\mathbit{$\mu${}}}_{\overline{p}}={$\mu${}}_{\overline{p}}\mathbit{S}/($\hbar${}/2)$ is given in terms of its spin $\mathbit{S}$ and the nuclear magneton (${$\mu${}}_{N}$) by ${$\mu${}}_{\overline{p}}/{$\mu${}}_{N}=-2.792\text{ }845\ifmmode\pm\else\textpm\fi{}0.000\text{ }012$. The 4.4 parts per million (ppm) uncertainty is 680 times smaller than previously realized. Comparing to the proton moment measured using the same method and trap electrodes gives ${$\mu${}}_{\overline{p}}/{$\mu${}}_{p}=-1.000\text{ }000\ifmmode\pm\else\textpm\fi{}0.000\text{ }005$ to 5 ppm, for a proton moment ${\mathbit{$\mu${}}}_{p}={$\mu${}}_{p}\mathbit{S}/($\hbar${}/2)$, consistent with the prediction of the $CPT$ theorem.