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

• Published in: Nature (London) Vol. 601; no. 7891; pp. 53 - 57
• Main Authors: Borchert, M J, Devlin, J A, Erlewein, S R, Fleck, M, Harrington, J A, Higuchi, T, Latacz, B M, Voelksen, F, Wursten, E J, Abbass, F, Bohman, M A, Mooser, A H, Popper, D, Wiesinger, M, Will, C, Blaum, K, Matsuda, Y, Ospelkaus, C, Quint, W, Walz, J, Yamazaki, Y, Smorra, C, Ulmer, S
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 06.01.2022
• Subjects: Antimatter; Antiparticles; Antiprotons; Asymmetry; Charge reversal; Charged particles; Confidence intervals; Cyclotrons; Equivalence principle; Magnetic fields; Magnetic moments; Mass ratios; Measurement methods; Methods; Particle physics; Physics; Protons; Quantum field theory; Ratios; Sensors; Spectroscopy; Spectrum analysis; Standard model (particle physics); Symmetry
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-021-04203-w

The standard model of particle physics is both incredibly successful and glaringly incomplete. Among the questions left open is the striking imbalance of matter and antimatter in the observable universe , which inspires experiments to compare the fundamental properties of matter/antimatter conjugates with high precision . Our experiments deal with direct investigations of the fundamental properties of protons and antiprotons, performing spectroscopy in advanced cryogenic Penning trap systems . For instance, we previously compared the proton/antiproton magnetic moments with 1.5 parts per billion fractional precision , which improved upon previous best measurements by a factor of greater than 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, [Formula: see text], is consistent with the fundamental charge-parity-time reversal invariance, and improves the precision of our previous best measurement by a factor of 4.3. The measurement tests the standard model at an energy scale of 1.96 × 10 gigaelectronvolts (confidence level 0.68), and improves ten coefficients of the standard model extension . Our cyclotron clock study also constrains hypothetical interactions mediating violations of the clock weak equivalence principle (WEP ) for antimatter to less than 1.8 × 10 , and enables the first differential test of the WEP using antiprotons . From this interpretation we constrain the differential WEP -violating coefficient to less than 0.030.