Precise measurement of positronium hyperfine splitting using the Zeeman effect

TL;DR

This paper reports a new high-precision measurement of positronium hyperfine splitting using the Zeeman effect, aiming to resolve discrepancies with QED predictions and explore potential new physics.

Contribution

It introduces a novel experimental method to measure positronium HFS with reduced systematic uncertainties, providing an independent check of previous results.

Findings

Current measurement: 203.3951 ± 0.0024 (stat.) ± 0.0019 (sys.) GHz

Discrepancy with QED prediction of 15 ppm (3.9σ) remains unresolved

Expected measurement precision within ppm within a year

Abstract

Positronium is an ideal system for the research of the quantum electrodynamics (QED) in bound state. The hyperfine splitting (HFS) of positronium, $\Delta_{\mathrm{HFS}}$, gives a good test of the bound state calculations and probes new physics beyond the Standard Model. A new method of QED calculations has revealed the discrepancy by 15\,ppm (3.9$\sigma$) of $\Delta_{\mathrm{HFS}}$ between the QED prediction and the experimental average. There would be possibility of new physics or common systematic uncertainties in the previous all experiments. We describe a new experiment to reduce possible systematic uncertainties and will provide an independent check of the discrepancy. We are now taking data and the current result of $\Delta_{\mathrm{HFS}} = 203.395\,1 \pm 0.002\,4 (\mathrm{stat.}, 12\,\mathrm{ppm}) \pm 0.001\,9 (\mathrm{sys.}, 9.5\,\mathrm{ppm})\,\mathrm{GHz} $ has been obtained so far. A measurement with a precision of $O$(ppm) is expected within a year.