Antiproton magnetic moment determined from the HFS of p¯He+

We report a determination of the antiproton magnetic moment, measured in a three-body system, independent of previous experiments. We present results from a systematic study of the hyperfine (HF) structure of antiprotonic helium where we have achieved a precision more than a factor of 10 better than our first measurement. A comparison between the experimental results and three-body quantum electrodynamic (QED) calculations leads to a new value for the antiproton magnetic moment μsp¯=−2.7862(83)μN, which agrees with the magnetic moment of the proton within 2.9×10−3.