Line-shape modeling in microwave spectroscopy of the positronium n=2 fine-structure intervals

Abstract

We report numerical simulations of positronium experiments designed to measure the n = 2 fine-structure intervals. The simulations include all possible interference effects between all 20 states in the n = 1 and laser-excited n = 2 manifolds as well as representations of the electric and magnetic fields present in the waveguides used in the experiments. We find that rf wave reflection from the vacuum chamber walls is a possible explanation of previously observed line-shape distortions and shifts. We also characterized several systematic effects, including those arising from quantum interference, that are likely to be significant for future measurements.

Positronium microwave spectroscopy using Ramsey interferometry

“…Thus, the measurement is not sensitive to the complete frequency response of the system, because it depends on the phase of the signal rather than its amplitude. Since variations in the frequency response seem to be the limiting factor of our previous Ps experiments [22], this would represent a significant advantage for improved Ps n = 2 fine structure measurements.…”

“…1. A standard [34] slow positron beam is produced using a 22 Na radioactive source with solid neon moderator [35]. Typical conical neon moderators have efficiencies of ≈ 0.5%.…”

“…However, despite the improved precision, a disagreement with theory was observed [14], as well as asymmetries in some of the measured lineshapes [15], suggesting the presence of unknown systematic effects. Subsequent numerical simulations of the experimental apparatus have indicated that reflections of microwave radiation in the vacuum chamber back into the waveguides may have been responsible for the observed asymmetries [22].…”