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.

Trapped antihydrogen in its ground state.

Antihydrogen atoms (H¯) are confined in an Ioffe trap for 15-1000 s-long enough to ensure that they reach their ground state. Though reproducibility challenges remain in making large numbers of cold antiprotons (p¯) and positrons (e(+)) interact, 5±1 simultaneously confined ground-state atoms are produced and observed on average, substantially more than previously reported. Increases in the number of simultaneously trapped H¯ are critical if laser cooling of trapped H¯ is to be demonstrated and spectroscopic studies at interesting levels of precision are to be carried out.