Revisiting ¹²⁹Xe electric dipole moment measurements applying a new global phase fitting approach

By measuring the spin precession frequencies of polarized 129Xe and 3He, a new upper limit on the 129Xe atomic electric dipole moment (EDM) was reported in Sachdev et al (2019 Phys. Rev. Lett. 123, 143003). Here, we propose a new evaluation method based on global phase fitting (GPF) for analyzing the continuous phase development of the 3He-129Xe comagnetometer signal. The Cramer-Rao lower bound on the 129Xe 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 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 at the 95% C.L.