Apparatus and Methods for a New Measurement of the Electron and Positron Magnetic Moments

Abstract

This thesis presents contributions to two precision measurement experiments: electron and positron $g/2$, and ATRAP antihydrogen spectroscopy. The magnetic moment of the electron in Bohr magnetons, $g/2$, is the most precisely measured fundamental property of an elementary particle, with an uncertainty of 0.28 parts per trillion. Positron $g/2$ is known a factor of 15 less precisely. Improvements in positron $g/2$ will improve on the best test of charge-parity-time (CPT) symmetry in leptons. Electron $g/2$ provides the most precise determination of $\alpha$, the fine structure constant. The comparison of this value with an independent measurement of $\alpha$ is the most precise test of the Standard Model of particle physics. A new apparatus has been built for making improved positron and electron $g/2$ measurements by performing quantum jump spectroscopy between the lowest quantum states of either particle trapped in a 100 mK cylindrical Penning trap. In this new apparatus, single cyclotron transitions of a single electron have been driven and detected in the precision measurement trap, and positrons have been trapped in a dedicated positron accumulation trap. This thesis describes progress toward improved $g/2$ measurements in this new apparatus. A new pulsed positron transfer system addresses significant challenges in transferring positrons into the precision measurement trap without compromising the single-particle detection system and control of the resonant microwave cavity mode structure. Helium is recovered, pressure tightly controlled, and vibrations mitigated in cryogen spaces critical for magnetic field stability. A parametric cavity mode detection technique for systematic $g/2$ corrections is demonstrated for the first time in the new apparatus. ATRAP is an experiment that aims to test CPT symmetry through precision spectroscopy of trapped antihydrogen. This thesis describes analytical quench propagation predictions and a new quick-turnoff system for ATRAP's Ioffe trap. These systems are important both for antihydrogen detection and for the protection of magnets in case of quenches.