A 16-parts-per-trillion measurement of the antiproton-to-proton charge-mass ratio

The standard model of particle physics is both incredibly successful and glaringly incomplete. Among the questions left open isthe striking imbalance of matter and antimatter in the observable universe(1), which inspires experiments to compare the fundamental properties of matter/antimatter conjugates with high precision(2-5). Our experiments deal with direct investigations of the fundamental properties of protons and antiprotons, performing spectroscopy in advanced cryogenic Penning trap systems(6). For instance, we previously compared the proton/antiproton magnetic moments with 1.5 parts per billion fractional precision(7,8), which improved upon previous best measurements(9) by a factor of greaterthan 3,000. Here we report on a new comparison of the proton/antiproton charge-to-mass ratios with a fractional uncertainty of 16 parts per trillion. Our result is based on the combination of four independent long-term studies, recorded in a total time span of 1.5 years. We use different measurement methods and experimental set-ups incorporating different systematic effects. The final result, -(q/m)(p)/(q/m)((p) over bar) =1.000000000003(16), is consistent with the fundamental charge-parity-time reversal invariance, and improvesthe precision of our previous best measurement' by a factor of4.3. The measurement teststhe standard model at an energy scale of 1.96 x 10(-27) gigaelectronvolts (confidence level 0.68), and improves ten coefficients ofthe standard model extension(10). Our cyclotron clock study also constrains hypothetical interactions mediating violations ofthe clock weak equivalence principle (WEPcc) for antimatterto less than 1.8 x 10(-7), and enablesthe first differential test ofthe WEP CC using antiprotons(11). From this interpretation we constrain the differential WEPcc-violating coefficient to less than 0.030.

Automated summary

The standard model of particle physics is incomplete in explaining the imbalance between matter and antimatter in the universe. This study focuses on investigating the fundamental properties of protons and antiprotons, specifically comparing their charge-to-mass ratios with high precision. The results provide insight into the standard model and improve the understanding of the properties of matter and antimatter.