Molecular enhancement factors for the P, T-violating electric dipole moment of the electron in BaCH₃ and YbCH₃ symmetric top molecules

Abstract

High-precision tests of fundamental symmetries are looking for the parity-(P), time-reversal-(T) violating electric dipole moment of the electron (eEDM) as proof of physics beyond the Standard Model. Particularly, in polyatomic molecules, the complex vibrational and rotational structure gives the possibility to reach high enhancement of the P,T-odd effects in moderate electric fields, and with the possibility of increasing the statistical sensitivity by using laser cooling. In this work, we calculate the P,T-odd molecular enhancement factor of the eEDM (W_d) and of the scalar-pseudoscalar interaction (Wₛ) necessary for the interpretation of future experiments on the promising candidates BaCH₃ and YbCH₃. We employ high-accuracy relativistic coupled cluster methods and systematically evaluate the uncertainties of our computational approach. Compared to other Ba- and Yb-containing molecules, BaCH₃ and YbCH₃ exhibit larger W_d and Wₛ associated to the increased covalent character of the M–C bond. The calculated values are 3.22 ± 0.12 × 10²⁴(hHz/ecm) and 13.80 ± 0.35 × 10²⁴(hHz/ecm) for W_d, and 8.42 ± 0.29 hkHz and 50.16 ± 1.27 hkHz for Wₛ, in BaCH₃ and YbCH₃, respectively. The robust, accurate, and cost-effective computational scheme reported in this work makes our results suitable for extracting the relevant fundamental properties from future measurements and also can be used to explore other polyatomic molecules sensitive to various violations of fundamental symmetries.