Cold, slow YbF molecules for measuring the electron’s electric dipole moment

Abstract

The Standard Model (SM), our current best framework of physics, has notable failings including its inability to account for the observed asymmetry of anti-matter to matter in the universe. This motivates theories beyond the SM. These beyond the SM theories introduce increased charge, parity (CP) symmetry breaking, as well as time symmetry violating effects. An electron with an electric dipole moment (eEDM) is an example of time symmetry violation, making eEDM searches crucial tests of these theories. The SM predicts that the eEDM is below 10^−35 e cm, while extensions to the SM predict higher values, in the range 10^−32 to 10^−24 e cm. The current best limit, set by the JILA group in 2023, is |dE | < 4.1 × 10^−30 e cm. Currently, molecular eEDM searches are often limited by short coherence times or low molecule numbers. To increase both, we propose measuring the eEDM using cooled YbF molecules, trapped in an optical lattice. In this thesis, we present the progress towards such a measurement with which an uncertainty of 10^−32 e cm should be achievable, testing most extensions to the SM. We use a two-stage cryogenic buffer gas source to produce a high flux molecular beam whose forward velocity is 49 m/s. We use radiation pressure slowing to decelerate this beam so that it can be captured in a magneto-optical trap, which we have built. We measure a leak out of the cooling cycle at a few parts in 10^4, which we attribute to low-lying states arising from inner-shell excitations which we call 4f-hole states. The electronic character and rotational structure of these 4f-hole states is studied.