Sixfold improved single particle measurement of the magnetic moment of the antiproton

Abstract

Our current understanding of the Universe comes, among others, from particle physics and cosmology. In particle physics an almost perfect symmetry between matter and antimatter exists. On cosmological scales, however, a striking matter/antimatter imbalance is observed. This contradiction inspires comparisons of the fundamental properties of particles and antiparticles with high precision. Here we report on a measurement of the g-factor of the antiproton with a fractional precision of 0.8 parts per million at 95% confidence level. Our value /2=2.7928465(23) outperforms the previous best measurement by a factor of 6. The result is consistent with our proton g-factor measurement gp/2=2.792847350(9), and therefore agrees with the fundamental charge, parity, time (CPT) invariance of the Standard Model of particle physics. Additionally, our result improves coefficients of the standard model extension which discusses the sensitivity of experiments with respect to CPT violation by up to a factor of 20.

A parts-per-billion measurement of the antiproton magnetic moment

“…(95% CL), and for the 68% CL we reported δ g/g = 520 p.p.b. 8 . The improvement factor quoted in the text compares the 68% confidence levels of the two measurements.…”

“…Experiments on mesons 2 , leptons 3,4 and baryons 5,6 have compared different properties of matter-antimatter conjugates with fractional uncertainties at the parts-per-billion level or better. One specific quantity, however, has so far only been known to a fractional uncertainty at the parts-per-million level 7,8 : the magnetic moment of the antiproton, μ p . The extraordinary difficulty in measuring μ p with high precision is caused by its intrinsic smallness; for example, it is 660 times smaller than the magnetic moment of the positron 3 .…”

“…Subsequently, the magnetron and the modified cyclotron modes of the particle are cooled by sideband drives and direct resistive cooling, respectively. To this end, the resonance frequency of the cyclotron detector is adjusted to ν +,PT , which couples the antiproton to the thermal bath of the detector with T d ≈ 12.8(8) K. The energy E +,L /k B of the modified cyclotron mode after such a thermalization cycle is analysed by measuring the axial frequency in the magnetic bottle B 2,AT of the analysis trap 8 . Once an antiproton with E +,L /k B < 0.05 K has been prepared, we keep it in the analysis trap and detune the resonance frequency of the cyclotron detector by approximately 800 kHz.…”

“…8, in this work the frequencies ν L and ν c are measured in the 85,000 times more homogeneous magnetic field of the precision trap. This greatly reduces the width of the g-factor resonance and thus enables measurements at a higher precision.…”

The race to reveal antimatter’s secrets

“…The group also uses a complex method to reveal the antiproton's magnetic moment 4 -akin to its intrinsic magnetism. The measurement involves switching individual particles rapidly between two separate traps and detecting changes caused by minuscule shifts in an oscillating microwave field.…”