The radon EDM apparatus

Fine and hyperfine interactions in 171YbOH and 173YbOH

The odd isotopologues of ytterbium monohydroxide, ^171,173YbOH, have been identified as promising molecules to measure parity (P) and time reversal (T) violating physics. Here, we characterize the òΠ_1/2(0,0,0)-X̃²Σ⁺(0,0,0) band near 577 nm for these odd isotopologues. Both laser-induced fluorescence excitation spectra of a supersonic molecular beam sample and absorption spectra of a cryogenic buffer-gas cooled sample were recorded. In addition, a novel spectroscopic technique based on laser-enhanced chemical reactions is demonstrated and used in absorption measurements. This technique is especially powerful for disentangling congested spectra. An effective Hamiltonian model is used to extract the fine and hyperfine parameters for the òΠ_1/2(0,0,0) and X̃²Σ⁺(0,0,0) states. A comparison of the determined X̃²Σ⁺(0,0,0) hyperfine parameters with recently predicted values [Denis et al., J. Chem. Phys. 152, 084303 (2020); K. Gaul and R. Berger, Phys. Rev. A 101, 012508 (2020); and Liu et al., J. Chem. Phys. 154,064110 (2021)] is made. The measured hyperfine parameters provide experimental confirmation of the computational methods used to compute the P,T-violating coupling constants W_d and W_M, which correlate P,T-violating physics to P,T-violating energy shifts in the molecule. The dependence of the fine and hyperfine parameters of the òΠ_1/2(0,0,0) and X̃²Σ⁺(0,0,0) states for all isotopologues of YbOH are discussed, and a comparison to isoelectronic YbF is made.

Pear-shaped atomic nuclei

This review presents the current status of experimental evidence for the occurrence of reflection-asymmetric or ‘pear’ shapes in atomic nuclei, which arises from the presence of strong octupole correlations in the nucleon–nucleon interactions. The behaviour of energy levels and electric octupole transition moments is reviewed, with particular emphasis on recent measurements. The relevance of nuclear pear shapes to measurements of fundamental interactions is also discussed.

Actinide and lanthanide molecules to search for strong CP-violation

Actinide and lanthanide molecules are prospective candidates to search for the violation of fundamental symmetries and test grand unification theories.

The observation of vibrating pear-shapes in radon nuclei

There is a large body of evidence that atomic nuclei can undergo octupole distortion and assume the shape of a pear. This phenomenon is important for measurements of electric-dipole moments of atoms, which would indicate CP violation and hence probe physics beyond the Standard Model of particle physics. Isotopes of both radon and radium have been identified as candidates for such measurements. Here, we observed the low-lying quantum states in ²²⁴Rn and ²²⁶Rn by accelerating beams of these radioactive nuclei. We show that radon isotopes undergo octupole vibrations but do not possess static pear-shapes in their ground states. We conclude that radon atoms provide less favourable conditions for the enhancement of a measurable atomic electric-dipole moment.

Coulomb excitation of pear-shaped nuclei

There is a large body of evidence that atomic nuclei can undergo octupole distortion and assume the shape of a pear. This phenomenon is important for measurements of electric-dipole moments of atoms, which would indicate CP violation and hence probe physics beyond the Standard Model of particle physics. Isotopes of both radon and radium have been identified as candidates for such measurements. Here, we have observed the low-lying quantum states in 224Rn and 226Rn by accelerating beams of these radioactive nuclei. We show that radon isotopes undergo octupole vibrations but do not possess static pear-shapes in their ground states. We conclude that radon atoms provide less favourable conditions for the enhancement of a measurable atomic electric-dipole moment.

CP-violating effect of the Th nuclear magnetic quadrupole moment: accurate many-body study of ThO

Investigations of CP violation in the hadron sector may be done using measurements in the ThO molecule. Recent measurements in this molecule improved the limit on the electron electric dipole moment (EDM) by an order of magnitude. Another time-reversal (T) and parity (P)-violating effect in 229ThO is induced by the nuclear magnetic quadrupole moment. We perform nuclear and molecular calculations to express this effect in terms of the strength constants of T, P-odd nuclear forces, neutron EDM, QCD vacuum angle θ, quark EDM, and chromo-EDM.

Time-reversal symmetry violation in molecules induced by nuclear magnetic quadrupole moments

Recent measurements in paramagnetic molecules improved the limit on the electron electric dipole moment (EDM) by an order of magnitude. Time-reversal (T) and parity (P) symmetry violation in molecules may also come from their nuclei. We point out that nuclear T, P-odd effects are amplified in paramagnetic molecules containing deformed nuclei, where the primary effects arise from the T, P-odd nuclear magnetic quadrupole moment (MQM). We perform calculations of T, P-odd effects in the molecules TaN, ThO, ThF+, HfF+, YbF, HgF, and BaF induced by MQMs. We compare our results with those for the diamagnetic TlF molecule, where the T, P-odd effects are produced by the nuclear Schiff moment. We argue that measurements in molecules with MQMs may provide improved limits on the strength of T, P-odd nuclear forces, on the proton, neutron, and quark EDMs, on quark chromo-EDMs, and on the QCD θ term and CP-violating quark interactions.