Title: Molecular laser spectroscopy at CRIS: opportunities for nuclear and beyond the standard model physics
Speaker: Carlos Fajardo-Zambrano
Abstract:
With the advancement laser of spectroscopic techniques at radioactive beam facilities, the spectroscopy of radioactive molecules has been achieved in recent years at ISOLDE (CERN) using the Collinear Resonance Ionization Spectroscopy (CRIS) experiment [1].
Thanks to their rich electronic structure and chemical properties, radioactive molecules are promising candidates for studies in different fields [2], including searches for CP-violating moments for beyond the standard model (BSM) searches [3-4]. Furthermore, heavy octupole deformed nuclei, such as 225,227Ac, are expected to be highly sensitive to nuclear CP-violating moments. Therefore, molecular studies involving 225,227Ac appear as one of the most compelling directions for nuclear CP-violation searches.
However, given its radioactive nature, no information was available on the electronic structure of AcF. Thus, the 2022 AcF experimental campaign at CRIS marks the first measurement of its electronic structure, where the strongest electronic transition from the X1Σ+ ground state is observed, along with an upper limit on its radiative lifetime [5].
Complementary to AcF, RaF has been proposed as a promising system for leptonic CP-violating studies due to its large intrinsic electric field and laser-coolable structure [6]. Following the successful measurement of 226RaF in low and high resolution [7-8], recent measurements of 223,225RaF at CRIS have enabled the first determination of the magnetic dipole and electric quadrupole moments in a radiative molecule [9]. Such measurements demonstrate the great sensitivity of molecules to nuclear magnetization distributions and the potential of radioactive molecules for nuclear structure studies.
This presentation will focus on the latest results of the CRIS collaboration on RaF and AcF, extending from nuclear structure measurements to preparatory studies for BSM measurements using molecular beams.
[1] Garcia Ruiz, R.F., et al. "Spectroscopy of short-lived radioactive molecules." Nature 581, 396-400 (2020).
[2] Opportunities for Fundamental Physics Research with Radioactive Molecules, arXiv:2302.02165 (2023)
[3] Kudashov, A. D., et al. "Ab initio study of radium monofluoride (RaF) as a candidate to search for parity-and time-and-parity–violation effects." Physical Review A 90, 052513 (2014).
[4] Osika, Y., & Shundalau, M. Fock-space relativistic coupled cluster study on the RaF molecule promising for the laser cooling. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 264, 120274 (2022).
[5] Athanasakis-Kaklamanakis, M., Au, M., Kyuberis, A., Zülch, C., Gaul, K., Wibowo, H., et al., Laser spectroscopy and CP-violation sensitivity of actinium monofluoride. arXiv preprint arXiv:2507.05224 (2025).
[6] Kudashov, A. D., et al. "Ab initio study of radium monofluoride (RaF) as a candidate to search for parity-and time-and-parity–violation effects." Physical Review A 90.5 (2014): 052513.
[7] Athanasakis-Kaklamanakis, M., Wilkins, S. G., Skripnikov, L. V., Koszorús, Á., Breier, A. A., Ahmad, O., et al., Electron correlation and relativistic effects in the excited states of radium monofluoride. Nature Communications, 16, 2139 (2025).
[8] S.-M. Udrescu, et al., Precision spectroscopy and laser-cooling scheme of a radium-containing molecule, Nature Physics 20, 202–207 (2024).
[9] S. G. Wilkins et al., Observation of the distribution of nuclear magnetization in a molecule, submitted (2023).
