Improved Measurement of the Magnetic Moment of the Antiproton

Today our article on an improved measurement of the magnetic moment of the antiproton, with a fractional precision of 0.8 parts in a million, was published in Nature Communications. This is, so far, the culmination point of 10 years of dedicated work on proton and antiproton magnetic moment measurements.

Previously, the magnetic moment of the antiproton has been extracted from exotic atom spectroscopy, with a fractional resolution on the 0.001-level. In 2013 the ATRAP collaboration published a 680-fold improved measurement using a single antiproton in a Penning trap. BASE was approved by CERN's research board in 2013 to contribute to this search. The result which is reported here follows the high-precision comparison of the antiproton-to-proton charge-to-mass ratio, and is the second fundamental physics measurement produced by BASE. By using the continuous Stern Gerlach effect in Penning traps, we performed non-destructive single-antiproton spin-transition spectroscopy to measure the particle's Larmor frequency. Combining this with measurements of the cyclotron frequency of the single trapped antiproton, the magnetic moment of the particle was obtained in units of the nuclear magneton, this ratio is also called "g-factor". Within the experimental uncertainties, our result (g/2)pbar=2.7928465(23) is consistent with our recent proton g-factor measurement (g/2)p=2.792847350(9), which supports the CPT invariance of the Standard Model. The result also improves constraints on coefficients of the prominent Standard Model extension by up to a factor of 22.

The much more precise measurement of the proton magnetic moment was carried-out by using the double Penning trap technique. A logical next step is the application of this much more challenging technique as well to measure the antiproton magnetic moment.

Together with very recent measurements carried out by ASACUSA and ALPHA, we are making rapid progress in our understanding of antimatter.


Further information:

RIKEN Press Release:

CERN Press Release:

MPI-K Press Release:

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