Systematic study and uncertainty evaluation of $P,T$-odd molecular enhancement factors in BaF

Abstract

A measurement of the magnitude of the electric dipole moment of the electron (eEDM) larger than that predicted by the Standard Model (SM) of particle physics is expected to have a huge impact on the search for physics beyond the SM. Polar diatomic molecules containing heavy elements experience enhanced sensitivity to parity ($P$) and time-reversal ($T$)-violating phenomena, such as the eEDM and the scalar-pseudoscalar (S-PS) interaction between the nucleons and the electrons, and are thus promising candidates for measurements. The NL-\textit{e}EDM collaboration is preparing an experiment to measure the eEDM and S-PS interaction in a slow beam of cold BaF molecules [Eur. Phys. J. D, 72, 197 (2018)]. Accurate knowledge of the electronic structure parameters, $W_d$ and $W_s$, connecting the eEDM and the S-PS interaction to the measurable energy shifts is crucial for the interpretation of these measurements. In this work we use the finite field relativistic coupled cluster approach to calculate the $W_d$ and $W_s$ parameters in the ground state of the BaF molecule. Special attention was paid to providing a reliable theoretical uncertainty estimate based on investigations of the basis set, electron correlation, relativistic effects and geometry. Our recommended values of the two parameters, including conservative uncertainty estimates, are 3.13 $\pm$ $0.12 \times 10^{24}\frac{\text{Hz}}{e\cdot \text{cm}}$ for $W_d$ and 8.29 $\pm$ 0.12 kHz for $W_s$.