BASE: Studies of Exotic Physis with Antiprotons and Protons
Dr. Stefan Ulmer (Ulmer Fundamental Symmetries Laboratory, RIKEN, Japan & CERN)

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 our universe, which inspires experiments to compare the fundamental properties of matter/antimatter conjugates with high precision. The BASE collaboration at the antiproton decelerator of CERN is performing such high-precision comparisons with protons and antiprotons. Using advanced, ultra-stable, cryogenic particle traps and superconducting detectors with single particle sensitivity, we have performed the most precise measurement of the proton-to-antiproton charge-to-mass ratio with a fractional uncertainty of 69 parts per trillion [1].

In another measurement, we have invented a novel spectroscopy method, which allowed for the first ultra-high precision measurement of the antiproton magnetic moment with a fractional precision of 1.5 parts in a billion [2]. Together with our recent measurement of the proton magnetic moment [3] this improves the precision of previous experiments [4] by more than a factor of 3000. A time series analysis of this recent magnetic moment measurement furthermore enabled us to set first direct constraints on the interaction of antiprotons with axion-like particles (ALPs) [5], and most recently, we have used our ultra-sensitive single particle detection systems to derive narrow-band constraints on the conversion of ALPs into photons [6].

In my talk I will review the recent achievements of BASE and will outline strategies to further improve our high-precision studies of matter-antimatter symmetry. This outlook will involve the implementation of sympathetic cooling of antiprotons using quantum logic methods, the development of the transportable antiproton trap BASE-STEP, and will also review recent experimental progress towards 10-fold improved measurements of the antiproton properties.

[1] S. Ulmer et al., Nature 524, 196 (2015).
[2] C. Smorra et al., Nature 550, 371 (2017).
[3] G. Schneider et al., Science 358, 1081 (2017).
[4] J. DiSciacca et al., Phys. Rev. Lett. 110, 130801 (2013).
[5] C. Smorra et al., Nature 575, 310 (2019).
[6] J. A. Devlin et al., Phys. Rev. Lett., accepted (2021).

S. Ulmer1, K. Blaum2, M. Bohman1,2, M. Borchert1,3, J. A. Devlin1,4, S. Erlewein1,2,4, M. Fleck1,5,
C. Smorra1, M. Wiesinger1,2, C. Will2, E. Wursten5, Y. Matsuda6, C. Ospelkaus3, W. Quint6, J. Walz7,8, Y. Yamazaki1
1RIKEN, Ulmer Fundamental Symmetries Laboratory, Saitama, Japan; 2Max-Planck-Institut für Kernphysik, Heidelberg, Germany; 3Leibnitz University, Hannover, Germany; 4CERN, Geneva, Switzerland; 5The University of Tokyo, Tokyo, Japan; 6GSI - Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany; 7Johannes Gutenberg-Universität, Mainz, Germany; 8Helmholtz-Institut Mainz, Germany;