Development for an improved comparison of proton-to-antiproton charge-to-mass ratio

Charge, Parity and Time (CPT) symmetry is known to be one of the most fundamental symmetries of the Standard Model of particle physics. As a consequence of CPT symmetry, it is predicted that fundamental properties of matter-antimatter conjugates are identical, apart from signs. Although no CPT violation has ever been observed, the unsolved mystery of matter-antimatter asymmetry in the universe has inspired experimental CPT tests in a variety of fields which compare these properties with high precision. As a part of such physics programs, the BASE collaboration has performed stringent CPT tests in the proton-antiproton system by Penning trap measurements, comparing as their charge-to-mass ratios and the magnetic moments. This thesis discusses the high-precision proton-to-antiproton comparison of the charge-to-mass ratios conducted by BASE. No CPT violation was observed at a relative precision of 6.9 × 10$^{−11}$ in a measurement carried out in 2014. Additional developmental works described in this thesis were performed since then to further improve the precision of the comparison. The principle of charge-to-mass ratio comparison is based on cyclotron frequency measurements of charged particles with a Penning trap. In case of the proton-to-antiproton comparison, cyclotron frequencies are compared between an antiproton and an H$^{−}$ ion rather than a proton, in order to avoid a systematic effect induced by polarity inversion of the trap. For improvement of the precision, a two-fold strategy was conceived. The first was to install a new image-current detection system in order to eliminate a source of the most dominant systematic error in the 2014 measurement. The other was to improve the cyclotron frequency stability and therefore to reduce of the statistical uncertainty. For this purpose, an improved magnetic field shielding was developed and environment conditions of the apparatus were optimized. These upgrades and developments have been installed and commissioned in BASE 2017 antiproton run, leading to a significantly improved measurement condition. Under this condition, an improvement of precision at least by a factor of 3 over the last measurement is expected.