Location: TRIUMF
Participating Canadian institutions: TRIUMF, Toronto, UBC
International partners: USA, Belgium, Germany, Netherlands, UK
In certain molecules, parity and time-reversal violation effects can be greatly enhanced compared to atomic systems 1. As these symmetry-violating effects scale with the atomic number, nuclear spin and nuclear deformation, measurements of molecular isotopologues containing heavy radioactive nuclei are predicted to provide unique and highly sensitive laboratories in these studies. However, experimental measurements of such radioactive molecules are scarce, and their study requires overcoming major experimental challenges. This research program at TRIUMF focuses on precision studies of radioactive molecules, which will offer new opportunities for the study of the nuclear electroweak structure and the violation of fundamental symmetries. The proximity of molecular states of different parity can enhance \(P\) and \(T\) violating sensitivity by orders of magnitude when compared to atomic systems. Moreover, certain radioactive molecules can contain heavy nuclei with octupole deformation, providing further sensitivity enhancements to explore \(P\) and \(T\) violation 2. The proposed program at ISAC/TRIUMF targets permanent electric dipole moments in systems with sensitivity to the electron’s EDM and \(P\),\(T\)-violating nuclear Schiff moments, as well as parity violation.
Radioactive ions will be produced at ISAC/ARIEL and sent into a cryogenic buffergas cell where molecules can be formed by interactions with the gas (see Fig. 1). The molecules will be extracted, selected and transferred to a cryogenic radiofrequency quadrupole trap, where the internal and translational temperature of the molecular ions will be reduced. Ions will be released with a kinetic energy of a few eV, neutralized, and decelerated down to sub-eV. Cold and slow molecular beams will be transported through a optical pumping region, where they can be transferred to a preferred molecular state. Subsequently, the molecular beam will interact with electric and magnetic fields. Finally, the population of a particular molecular state can be studied for different configurations of the external fields, providing information on a specific symmetry-violating effect.
In a first stage, the formation and properties of RaF will be studied 3, followed by precision spectroscopy (at the MHz level) of the hyperfine structure. Next would be optical pumping and radiofrequency spectroscopy with kHz resolution, and the production of slow, cold RaF beams. Finally, spectroscopy at the Hz level, in the presence of electric and magnetic fields, has to be demonstrated, to measure parity violating effects in a molecular beam. Subsequently, a magneto-optical trap for RaF would be attempted. Post 2025, such a setup could be used to carry about competitive EDM searches, with increasing precision over 3 to 5 years. Collaborators at MIT, Caltech, Edinburgh, and TRIUMF have started on developing the required tools and techniques.
Similarly, the broader AMO community has established techniques to construct trapped cold diatomic molecules from separate laser-cooled atoms, possibly providing very long coherence times for EDM experiments. There is ongoing consideration in the community to form diatomic molecules with octupole-deformed laser-cooled \(^{223,225}\)Ra and \(^{223}\)Fr as the heavy atom. Since low-\(Z\) alkali atom partners do not produce dimers with useful sensitivity to EDM effects, the challenge is to develop useful atomic partners which are inherently more difficult to laser cool.