A partsperbillion measurement of the antiproton magnetic moment
Abstract
Precise comparisons of the fundamental properties of matterantimatter conjugates provide sensitive tests of chargeparitytime (CPT) invariance, which is an important symmetry that rests on basic assumptions of the standard model of particle physics. Experiments on mesons, leptons and baryons have compared different properties of matterantimatter conjugates with fractional uncertainties at the partsperbillion level or better. One specific quantity, however, has so far only been known to a fractional uncertainty at the partspermillion level: the magnetic moment of the antiproton, . The extraordinary difficulty in measuring with high precision is caused by its intrinsic smallness; for example, it is 660 times smaller than the magnetic moment of the positron. Here we report a highprecision measurement of in units of the nuclear magneton μ_{N} with a fractional precision of 1.5 parts per billion (68% confidence level). We use a twoparticle spectroscopy method in an advanced cryogenic multiPenning trap system. Our result = 2.7928473441(42)μ_{N} (where the number in parentheses represents the 68% confidence interval on the last digits of the value) improves the precision of the previous best measurement by a factor of approximately 350. The measured value is consistent with the proton magnetic moment, μ_{p} = 2.792847350(9)μ_{N}, and is in agreement with CPT invariance. Consequently, this measurement constrains the magnitude of certain CPTviolating effects to below 1.8 × 10^{24} gigaelectronvolts, and a possible splitting of the protonantiproton magnetic moments by CPTodd dimensionfive interactions to below 6 × 10^{12} Bohr magnetons.
 Publication:

Nature
 Pub Date:
 October 2017
 DOI:
 10.1038/nature24048
 Bibcode:
 2017Natur.550..371S