Direct measurement of transition frequencies in isolated $\overline{p}He^{+}$ atoms, and new CPT-violation limits on the antiproton charge and mass

A radio frequency quadrupole decelerator and achromatic momentum analyzer were used to decelerate antiprotons and produce p/sup 4/He /sup +/ and p/sup 3/He/sup +/ atoms in ultra-low- density targets, where collision-induced shifts of the atomic transition frequencies were negligible. The frequencies at near-vacuo conditions were measured by laser spectroscopy to fractional precisions of (6-19)*10 /sup -8/. By comparing these with QED calculations and the antiproton cyclotron frequency, we set a new limit of 1*10/sup -8/ on possible differences between the antiproton and proton charges and masses. (18 refs).