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 (p) and proton (p) by almost a factor of 10⁶ over earlier exotic atom measurements, and is the most precise CPT test with baryons by a similar large factor. Measuring the cyclotron frequencies of a simultaneously trapped p and H ion establishes that the ratio of q/m for p and p is -0.99999999991 ± 0.00000000009, more than 10 times the accuracy over our previous measurement. This 9 × 10^-11 comparison makes the first use of simultaneously trapped particles for sub-ppb spectroscopy.