One-Particle Measurement of the Antiproton Magnetic Moment

For the first time a single trapped antiproton ($\overline{p}$) is used to measure the $\overline{p}$ magnetic moment ${\mathbit{\ensuremath{\mu}}}_{\overline{p}}$. The moment ${\mathbit{\ensuremath{\mu}}}_{\overline{p}}={\ensuremath{\mu}}_{\overline{p}}\mathbit{S}/(\ensuremath{\hbar}/2)$ is given in terms of its spin $\mathbit{S}$ and the nuclear magneton (${\ensuremath{\mu}}_{N}$) by ${\ensuremath{\mu}}_{\overline{p}}/{\ensuremath{\mu}}_{N}=\ensuremath{-}2.792\text{ }845\ifmmode\pm\else\textpm\fi{}0.000\text{ }012$. 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 ${\ensuremath{\mu}}_{\overline{p}}/{\ensuremath{\mu}}_{p}=\ensuremath{-}1.000\text{ }000\ifmmode\pm\else\textpm\fi{}0.000\text{ }005$ to 5 ppm, for a proton moment ${\mathbit{\ensuremath{\mu}}}_{p}={\ensuremath{\mu}}_{p}\mathbit{S}/(\ensuremath{\hbar}/2)$, consistent with the prediction of the $CPT$ theorem.

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