Precision spectroscopy studies of radioactive molecules for fundamental physics

Precision molecular experiments provide a unique tool in the search for physics beyond the Standard Model (SM) and exploration of the fundamental forces of nature. Molecules can offer more than eleven orders of magnitude enhancement in the sensitivity to fundamental symmetries violation compared to atoms, facilitating precision tests of the SM and the possibility to probe energy scales beyond hundreds of TeV. The radium monofluoride (RaF) molecule is expected to be particularly sensitive to symmetry violating effects at the nuclear level, due to the octupole deformation of certain Ra nuclei. In this talk, I will present the results obtained from a series of laser spectroscopy experiments performed on short-lived RaF molecules at the ISOLDE facility at CERN. Using a collinear resonant ionization setup, the rotational and hyperfine structure of ²²⁶RaF and ²²⁵RaF were measured with high precision [1,2]. This allowed the observation for the first time of the effect of the distribution of the nuclear magnetization on the energy levels of a molecule [2] and the quantification of a feasible laser cooling scheme for RaF molecules [1,3]. These results represent an increase in precision of almost 3 orders of magnitude relative to our previous studies [4,5]. This opens the way for future precision studies and new physics searches in these systems.

1. 1. Udrescu, S.-M., Wilkins, S.G., et al. "Precision spectroscopy and laser-cooling scheme of a radium-containing molecule." Nature Physics 20.2 (2024): 202-207.
   
   2. Wilkins, S.G., Udrescu, S.-M., et al. "Observation of the distribution of nuclear magnetization in a molecule." arXiv preprint arXiv:2311.04121 (2023).
   
   3. Athanasakis-Kaklamanakis, M., et al. "Radiative lifetime of the A²Pi_1/2 state in RaF with relevance to laser cooling." arXiv preprint arXiv:2403.09336 (2024).
   
   4. Udrescu, S.-M., et al. "Isotope shifts of radium monofluoride molecules." Physical Review Letters 127.3 (2021): 033001.
   
   5. Garcia Ruiz, R.F., et al. "Spectroscopy of short-lived radioactive molecules." Nature 581.7809 (2020): 396-400.