Measurement of the antiproton magnetic moment and mass

We report a reanalysis of our $\overline{p}$ x-ray data from Pb and U for fine-structure splitting and have included perturbations to the $\overline{p}$-atomic energy levels arising from radiative corrections, relativistic effects, electron screening, finite nuclear size, and nuclear recoil. The value for the antiproton magnetic moment is -2.817 ± 0.048 nuclear magnetons which is 0.1% lower than our previous result and in agreement with the CPT prediction of -2.793. In addition we have obtained a value for the $\overline{p}$ mass from the measured $\overline{p}-\mathrm{Pb}$ x-ray transition energies from $n=15\mathrm{}$ to $n=10\mathrm{}$ The resulting mass 938.30 ± 0.13 MeV is in good agreement with the CPT prediction that the $\overline{p}$ mass should equal the proton mass. We find $m_p-m_{\overline{p}}=-0.02\mathrm{}\pm 0.13$ MeV.