One-particle measurement of the antiproton magnetic moment.

For the first time a single trapped antiproton (p) is used to measure the p magnetic moment μ(p). The moment μ(p)=μ(p)S/(ℏ/2) is given in terms of its spin S and the nuclear magneton (μ(N)) by μ(p)/μ(N)=-2.792 845±0.000 012. The 4.4 parts per million (ppm) uncertainty is 680 times smaller than previously realized. Comparing to the proton moment measured using the same method and trap electrodes gives μ(p)/μ(p)=-1.000 000±0.000 005 to 5 ppm, for a proton moment μ(p)=μ(p)S/(ℏ/2), consistent with the prediction of the CPT theorem.