Precision measurements in diatomic molecules: a route to a permanent electric dipole moment

The universe can be successfully described in terms of elementary particles. The Standard Model of particle physics unifies their properties and interactions and describes almost all physical phenomena we observe. However, cosmological observations and theoretical arguments indicate that the Standard Model is incomplete. It needs to be extended with new yet unknown particles. The NL-eEDM experiment searches for indirect effects of these new particles by measuring the permanent electric dipole moment (EDM) of the barium monofluoride molecule. An EDM leads to an interaction of the molecule with the electric field that violates both parity and time-reversal symmetry. Despite many attempts, an EDM has not been observed yet in any system. However, the upper limits set by experiments become stronger every time.

To improve the limit on EDMs, both high precision and high accuracy in experiments searching for EDMs are needed. In this thesis, we present a theoretical description of the NL-eEDM experiment required to interpret the measurement outcomes and evaluate its accuracy.
Besides, we develop a new measurement method to measure the accuracy without compromising the precision of the EDM. We successfully applied this method in the NL-eEDM experiment. We demonstrate that parameters, such as the electric field, can be measured up to the precision required for a limit on the EDM.