In a paper just published in Nature we report on the first direct high precision measurement of the proton magnetic moment. By application of the elegant double Penning trap technique we achieved a fractional precision of 3.3 parts per billion. Our value is consistent with the currently accepted CODATA value, but 2.5 times more precise.
The currently most precise value of the proton magnetic moment is based on spectroscopy of the ground state hyperfine splitting of atomic hydrogen in a magnetic field using a MASER. From these experiments, carried out about 42 years ago, the proton magnetic moment is extracted using input of two independent experiments and bound state corrections at the level of 17.7 ppm. In contrast, we measured the magnetic moment of a single trapped proton directly, which is about 760 times more precise than any direct measurement performed so far.
The double trap measuring-scheme can be directly applied to measure the magnetic moment of a single trapped antiproton, which is planned at the BASE-CERN experiment, currently being setup for the AD antiproton run 2014. The magnetic moment of the antiproton has recently been measured by the ATRAP collaboration with a fractional precision of 4.4ppm, which is 680 times more precise than values extracted from antiprotonic helium spectroscopy performed by the ASACUSA collaboration. In BASE we plan to apply the double trap scheme to improve the 4.4ppm value by more than a factor of 1000. This will constitute a stringent test of CPT invariance with baryons.
Andreas Mooser, first author of the paper, just joined the BASE-team at CERN. His post-doctoral research will be funded by one of the highly competitive RIKEN foreign post-doctoral researchers fellowships.
http://www.nature.com/nature/journal/v509/n7502/full/nature13388.html (Original Manuscript)
http://www.nature.com/nature/journal/v509/n7502/full/509571a.html (News and Views Article by A. Kostelecky)
http://www.nature.com/news/proton-s-magnetism-measured-with-greatest-precision-yet-1.15310 (Promoting article by Nature News)
http://www.riken.jp/en/pr/press/2014/20140529_1/ (RIKEN press release)