Probing the Energy Structure of Positronium with a 203 GHz Fabry-Perot Cavity

TL;DR

This paper discusses a new direct measurement approach for the positronium hyperfine splitting at 203 GHz using a gyrotron and a high-finesse Fabry-Perot cavity, aiming to reduce systematic errors present in previous indirect methods.

Contribution

It introduces a novel experimental setup that eliminates the need for static magnetic fields in measuring Ps-HFS, potentially improving accuracy and resolving existing discrepancies.

Findings

Development of a high-power 203 GHz radiation source using a gyrotron.

Design and optimization of a high-finesse Fabry-Perot cavity for positronium experiments.

Current progress in experimental setup and future plans for direct Ps-HFS measurement.

Abstract

Positronium is an ideal system for the research of the bound state QED. The hyperfine splitting of positronium (Ps-HFS: about 203 GHz) is sensitive to new physics beyond the Standard Model via a vacuum oscillation between an ortho-Ps and a virtual photon. Previous experimental results of the Ps-HFS show 3.9 sigma(15 ppm) discrepancy from the QED calculation. All previous experiments used an indirect method with static magnetic field to cause Zeeman splitting (a few GHz) between triplet states of ortho-Ps, from which the HFS value was derived. One possible systematic error source of the indirect method is the static magnetic field. We are developing a new direct measurement system of the Ps-HFS without static magnetic field. In this measurement we use a gyrotron, a novel sub-THz light source, with a high-Finesse Fabry-Perot cavity to obtain enough radiation power at 203 GHz. The present status of the optimization studies and current design of the experiment are described.