Precision Mass Spectroscopy of the Antiproton and Proton Using Simultaneously Trapped Particles

This last of a series of three measurements improves the comparison of antiproton $\left(\overline{p}\right)$ and proton $\left(p\right)$ by almost a factor of ${10}^6$ over earlier exotic atom measurements, and is the most precise $\mathrm{CPT}$ test with baryons by a similar large factor. Measuring the cyclotron frequencies of a simultaneously trapped $\overline{p}$ and $H^{-}$ ion establishes that the ratio of $q/m$ for $\overline{p}$ and $p$ is $-0.999\mathrm{}99999991\pm 0.00000000009$, more than 10 times the accuracy over our previous measurement. This $9\times {10}^{-11\mathrm{}}$ comparison makes the first use of simultaneously trapped particles for sub-ppb spectroscopy.