In a paper published today in Nature, the BASE collaboration reports on the most precise comparison yet between a fundamental property of protons and antiprotons. Analysing a total of about 24000 proton and antiproton cyclotron frequency measurements, taken over the course of 1.5 years, we found that the charge-to-mass ratios of protons and antiprotons are identical to within a record experimental uncertainty of 16 parts per trillion. This confirms that a fundamental symmetry in the Standard Model - the so-called CPT invariance - is valid with 4-fold improved resolution.
In addition, we placed stringent limits on the weak equivalence principle for matter and antimatter clocks. According to this principle, different bodies in the same gravitational field experience the same acceleration. Because our experiment is placed on the surface of the Earth, the proton and antiproton cyclotron-frequency measurements were made in the gravitational field on Earth’s surface. Sampling the varying gravitational field in our laboratory as the planet orbits around the Sun, if matter and antimatter would react differently to gravity, we should observe time dependent signatures in the measured proton/antiproton cyclotron frequency ratios. We did not find such oscillating signatures and our measurements show that the difference in the gravitational force must be smaller than 3 %. This study constitutes the first differential test of the weak equivalence principle for baryonic matter/antimatter clocks, the result indicates, within the achieved experimental resolution, that matter and antimatter behave similar under gravity.
Link to the publication: A 16 parts per trillion comparison of the proton/antiproton charge-to-mass ratios
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Link to the Fundamental Symmetries Lab at RIKEN: News post about this article
Image Credits: Stefan Ulmer / RIKEN