BASE collaboration compares protons and antiprotons with an unprecedented precision

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view of BASE experiment at CERN
View of the BASE experiment (Image: CERN)

In a paper published in the journal Nature, the BASE collaboration at CERN reports the most precise comparison yet between protons and antiprotons, the antimatter counterparts of protons.

Analysing proton and antiproton measurements taken over a year and a half at CERN’s antimatter factory, a unique facility for antimatter production and analyses, the BASE team measured the electric charge-to-mass ratios of the proton and the antiproton with record precision. The results found these are identical to within an experimental uncertainty of 16 parts per trillion.

This result represents the most precise direct test of a fundamental symmetry between matter and antimatter, performed with particles made of three quarks, known as baryons, and their antiparticles,” says AVA Supervisor and BASE spokesperson Stefan Ulmer.

This result is four times more precise than the previous best comparison between these ratios, and the charge-to-mass ratio is now the most precisely measured property of the antiproton.” says Stefan Ulmer. “To reach this precision, we made considerable upgrades to the experiment and carried out the measurements when the antimatter factory was closed down, using our reservoir of antiprotons, which can store antiprotons for years.” Making cyclotron-frequency measurements when the antimatter factory is not in operation is ideal, because the measurements are not affected by disturbances to the experiment’s magnetic field.

In addition to comparing protons and antiprotons with an unprecedented precision, the BASE team used their measurements to place stringent limits on models beyond the Standard Model that violate CPT symmetry, as well as to test a fundamental physics law known as the weak equivalence principle.

Full report via 

Full Article in Nature (Open Access)

Borchert, M.J., Devlin, J.A., Erlewein, S.R. et al. A 16-parts-per-trillion measurement of the antiproton-to-proton charge–mass ratio. Nature 601, 53–57 (2022).