Revisiting $^{129}$Xe electric dipole moment measurements applying a new global phase fitting approach

TL;DR

This paper introduces a new global phase fitting method for analyzing $^{129}$Xe EDM measurements, improving data utilization and robustness, leading to a refined upper limit on the $^{129}$Xe atomic electric dipole moment.

Contribution

The paper presents a novel global phase fitting approach for analyzing comagnetometer signals, enhancing the precision and robustness of $^{129}$Xe EDM measurements.

Findings

New upper limit on $^{129}$Xe EDM: < 8.3 x 10^{-28} e cm at 95% C.L.

The GPF method reduces systematic uncertainties related to phase drift.

Improved data analysis allows inclusion of previously unusable data.

Abstract

By measuring the nuclear magnetic spin precession frequencies of polarized $^{129}$Xe and $^{3}$He, a new upper limit on the $^{129}$Xe atomic electric dipole moment (EDM) $ d_\mathrm{A} (^{129}\mathrm{Xe})$ was reported in Phys. Rev. Lett. 123, 143003 (2019). Here, we propose a new evaluation method based on global phase fitting (GPF) for analyzing the continuous phase development of the $^{3}$He-$^{129}$Xe comagnetometer signal. The Cramer-Rao Lower Bound on the $^{129}$Xe EDM for the GPF method is theoretically derived and shows the potential benefit of our new approach. The robustness of the GPF method is verified with Monte-Carlo studies. By optimizing the analysis parameters and adding data that could not be analyzed with the former method, we obtain a result of $d_\mathrm{A} (^{129}\mathrm{Xe}) = 1.1 \pm 3.6~\mathrm{(stat)} \pm 2.0~\mathrm{(syst)} \times 10^{-28}~ e~\mathrm{cm}$ in an unblinded analysis. For the systematic uncertainty analyses, we adopted all methods from the aforementioned PRL publication except the comagnetometer phase drift, which can be omitted using the GPF method. The updated null result can be interpreted as a new upper limit of $| d_\mathrm{A} (^{129}\mathrm{Xe}) | < 8.3 \times 10^{-28}~e~\mathrm{cm}$ at the 95\% C.L.