Session C14: Minisymposium: Fundamental Symmetries I - Atom, Molecule

Electric dipole moment of the electron with ThO molecule

The Standard Model of particle physics accurately describes all fundamental particles discovered so far. However, it is unable to address two great mysteries in physics, the nature of dark matter and why matter dominates over antimatter throughout the Universe. Novel theories beyond the Standard Model may explain these phenomena. These models predict very massive particles whose interactions violate time-reversal (T) symmetry and would give rise to an electric dipole moment (EDM) along the electron’s spin. Thus, searching for EDM provides a powerful probe to these new physics and sheds light on the mystery of the matter-antimatter asymmetry of the Universe.

Here, I share with you the exciting journey of the ACME electron EDM search that has set the recent best limit on the value of electron EDM, measured by spin precession in a superposition of quantum states in cold molecules. New upgrades employing various quantum control and atomic physics techniques are recently demonstrated, projecting over an order of magnitude sensitivity enhancement for the next EDM search. These development severely constrains T-violating new physics in 10~100 TeV energy range, exceeding what can be reached at the Large Hadron Collider.   

Electron EDM search with laser-cooled heavy elements"

The large imbalance in the amounts of matter and antimatter currently observed in the universe demands physics beyond the standard model, which violates fundamental symmetries. Recently, the search for a non-zero permanent electric dipole moment (EDM) of an elementary particle has taken place actively world-wide, because the existence of EDM violates charge conjugation parity symmetry. It is predicted that the EDM of an electron (eEDM) is enhanced in paramagnetic atoms. Francium (Fr), being the heaviest alkali element, is known to possess the largest eEDM enhancement factor amongst any ground-state atom. Therefore, we aim to search for the eEDM with unprecedented precision using Fr atoms trapped in an optical lattice. In this talk, the current status of the Fr experiment conducted at RIKEN Nishina center will be presented.   

Radioactive Molecules for Studies of Fundamental Symmetries

Recent advances in precise control and study of molecules have opened up new opportunities for fundamental physics research. Radioactive molecules, in particular, can be artificially created to contain nuclei with extreme proton-to-neutron ratios, providing an extreme sensitivity to symmetry-violating nuclear properties. Precision measurements of these systems can offer unique and complementary laboratories in our search for new physics. In this talk, I will present recent highlights and perspectives from laser spectroscopy experiments on these exotic species.   

Table-top synthesis, cooling, and spectroscopy of radioactive molecules for symmetry violation searches.

Radioactive molecules are highly sensitive platforms for studies of fundamental nuclear and particle physics due to their large enhancements of CP-violating electromagnetic moments. However, practical challenges associated with producing the necessary quantities of these molecules have made their study difficult. We discuss a table-top, cryogenic buffer gas system capable of high-resolution spectroscopy on microgram-scale quantities of rare isotope molecules. Using this apparatus, we synthesize, cool, and perform high-resolution spectroscopy on radium-226 hydroxide (RaOH) molecules for the first time. RaOH is a promising candidate for next-generation symmetry violation searches, such as the Schiff moment and electron's electric dipole moment, due to the static octupole deformation of the radium nucleus and the predicted laser-coolability of the molecule.   

Fundamental symmetries via quantum sensing with polyatomic molecules

Atoms and molecules are sensitive proves of the nucleus, including collective nuclear CP-violating effects such as magnetic quadrupole moments and nuclear Schiff moments. Molecules provide high intrinsic sensitivity due to their ability to be efficiently polarized in the laboratory frame, but their complex structure presents many experimental challenges. In this talk we discuss using engineered polyatomic molecules which combine high polarizability, optical control for advanced quantum sensing, and high intrinsic sensitivity to symmetry violations. We provide an update for two ongoing experiments at Caltech: a nuclear magnetic quadrupole moment search in 173YbOH, and the production, cooling, and spectroscopy of 226RaOH using methods which would be applicable to other radioactive species.   

Progress towards a nuclear Schiff moment measurement using 205TlF molecules in CeNTREX

The aim of CeNTREX (Cold molecule Nuclear Time-Reversal EXperiment) is to search for the time-reversal and parity-violating Schiff moment of the 205Tl nucleus. With the expected experimental sensitivity we would be able to set competitive bounds on θ_QCD, quark chromo electric dipole moments (EDMs), and the proton EDM. The energy shift resulting from the 205 Tl Schiff moment is amplified in the polar molecule thallium fluoride (TlF), relative to the case in atoms. We employ two methods to maximize population in the science state used in the measurement: rotational cooling to pump several rotational states into a single hyperfine level of the J=0 rotational level of the ¹Σ⁺ electronic ground state and electrostatic focusing with a quadrupole lens. Rotational cooling pumps population into the J=0 state, but the electrostatic lens requires a weak field seeking state with J=2 and the science state has J=1. This requires multiple quantum state transfer stages, which we perform using adiabatic passage with microwaves. Finally, the Schiff moment measurement requires nulling of the magnetic fields in the interaction region to within 10 uG, which is achieved with a combination of passive magnetic shielding and shim coils. This talk will discuss progress towards the nuclear Schiff moment measurement.   

A new search for flavor-conserving hadronic CP violation using ultracold assembled 223FrAg molecules

We present a new approach to search for flavor-conserving hadronic CP violation (FCH-CPV) by measuring the ²²³Fr nuclear Schiff moment. The ²²³Fr nucleus (t_1/2 = 22 minutes) is believed to have a static octupole deformation that leads to a ~300-fold enhancement in the size of its Schiff moment, for a given strength of FCH-CPV  interactions [1]. The observable CP-violating energy shift induced when electrons interact with the Schiff moment is further amplified (relative to the shift in Fr atoms) when ²²³Fr is bound in a strongly ionic molecule. Binding Fr and Ag to form francium-silver (FrAg) creates such a polar molecule [2,3]. Because both species have alkali-like atomic structures, all modern atomic physics techniques such as laser cooling, controllable interactions via Feshbach resonances, and optical trapping can be applied to them. This will enable the assembly of ultracold  ²²³FrAg molecules using well-established methods [4]. Assuming experimental parameters for molecule number, nuclear spin coherence time, and detection efficiency that have already been demonstrated in other experiments that use ultracold assembled molecules, we project a factor of ~1000 improvement in underlying FCH-CPV physics for the first generation of an experiment. In this talk, we present progress towards creating ²²³FrAg by demonstrating magneto-optical trapping of silver atoms and studies towards measuring ultracold Ag-Ag scattering properties. We also present progress towards developing an offline ²²³Fr source.

[1] Spevak, V., et al. (1997). Enhanced T-odd, P-odd electromagnetic moments in reflection asymmetric nuclei. Phys. Rev. C, 56(3), 1357.

[2] Fleig, T., & DeMille, D. (2021). Theoretical aspects of radium-containing molecules amenable to assembly from laser-cooled atoms for new physics searches. New J. Phys., 23(11), 113039.

[3] Śmiałkowski, M., & Tomza, M. (2021). Highly polar molecules consisting of a copper or silver atom interacting with an alkali-metal or alkaline-earth-metal atom. Phys. Rev. A, 103(2), 022802.

[4] Kłos, J., et al. (2022). Prospects for assembling ultracold radioactive molecules from laser-cooled atoms. New J. Phys., 24(2), 025005.   

Progress towards a search for CP-violating nuclear Schiff moments using molecules in solids

Nuclear Schiff moments (NSMs) present a powerful probe into new physics through their connection to CP-symmetry violation. Such symmetry violations are needed to explain the observed baryon asymmetry of the Universe. We are investigating the application of molecular matrix methods[1] to the search for NSMs of pear-shaped nuclei in heavy polar radioactive molecules[2]. Pear-shaped nuclei (i.e. those with both octupole deformations), such as ²²⁵Ra, are expected to have enhanced NSMs[3]. These methods involve trapping polar molecules in a noble gas matrix, which is predicted to lock their orientation relative to the matrix lattice vectors. This contribution focuses on the FRIB-EDM3 instrument, which consists of two main parts.

The frontend will create and mass-separate molecular ions, such as RaF. Electrospray ionization will be used to create the molecular ions, then a series of ion optics will introduce the ions to vacuum and perform mass separation[4].

The backend will neutralize the ions, co-deposit them in a noble gas matrix, and perform molecular hyperfine spectroscopy, which will ultimately enable an NSM search.

We believe that this approach may be an efficient method for creating and trapping radioactive molecules starting from a precursor solution made available by the Isotope Harvesting Program at FRIB. Our initial goal is to quantify and optimize the efficiency of this approach. Eventually we aim to carry out a sensitive search for the NSM of ²²⁵Ra using, for example, RaF molecules in solid argon. We will provide an update on the current status of the instrument as well as calculations relevant to developing an NSM measurement scheme.

[1] A.C. Vutha et al, PRA 98, 032513 (2018).

[1] G. Arrowsmith-Kron et al, (2023), arXiv:2302.02165.

[3] N. Auerbach et al, PRL 76, 4316 (1996).

[4] J. Ballof et al, NIMB 541, 224 (2023).   

Ab Initio Calculation of Schiff Moments in Heavy Nuclei

Interpreting the results of experiments to measure electric dipole moments in certain atoms and molecules requires one to compute the dependence of the nuclear Schiff moment on underlying sources of CP violation. Here we extend the valence-space In-Medium Similarity Renormalization Group so that it includes the parity- and time-reversal-violating nucleon-nucleon interaction created by CP-violating particle physics alongside the usual chiral strong interaction. We apply the new scheme to 199Hg, the isotope with the best experimental limit on its atomic dipole moment, and to other heavy nuclei.   

Prospects for Calibrating the New Physics Sensitivity of 229Pa

A non-zero permanent electric dipole moment (EDM) would violate parity (P) and time-reversal (T) symmetry, and through the CPT theorem, charge-parity (CP) symmetry is also violated. New sources of CP-violation are necessary to explain the observed baryon asymmetry of the Universe.  Detecting a non-zero EDM with current or planned levels of sensitivity would provide evidence for new sources of CP-violation. This nuclear EDM is partially screened by its atomic electrons which are described by the Nuclear Schiff Moment (NSM). The NSM is responsible for inducing the atomic EDM we are seeking to observe.  We aim to search for a nearly degenerate ground state parity doublet in ²²⁹Pa (Z = 91, τ=1.5 d, I=5/2). If this parity doublet exists, which is thought to have energy splitting consistent with 60 ± 50 eV, then this would significantly enhance the lab-frame NSM and would provide strong motivation for a future search for an NSM of ²²⁹Pa, which may be 10⁶ times larger than the NSM for ¹⁹⁹Hg. In this presentation, gamma-ray and internal conversion spectroscopy techniques are being explored in order to determine the precise nature of the parity doublet if it exists.   

Towards a More Sensitive Search for the Atomic EDM of Radium Using Laser Cooling and Trapping

Searches for the atomic electric dipole moment (EDM) of diamagnetic atoms is primarily sensitive to charge-parity-(CP)-violation originating within the nuclear medium and are motivated by the observed and unexplained baryon asymmetry of the universe. The Radium-225 isotope, which has a two week half-life, has a large octopole ("pear-shaped") nuclear deformation which is expected to enchance its nuclear Schiff moment by about three orders of magnitude compared to the Hg-199 isotope which currently sets some of the best limits on new sources of CP-violation in the hadronic sector. The Ra EDM experiment utilizes laser probing to measure the spin precession of laser cooled and trapped atoms in its search for an EDM. A variety of upgrades for the experiment are underway which, when combined, are expected to improve the statistical sensitivity of the experiment by at least two orders of magnitude. A new laser cooling scheme, utilizing a stronger atomic transition, will increase the atom trapping efficiency by two orders of magnitude. In addition, a new high voltage apparatus capable of a factor of 7 higher electric field (E-field) as well as a more well-controlled E-field reversal is under development. A new laser-based spin-precession readout scheme, demonstrated recently for a similar search using Yb-171 atoms, is being adapted for Ra-225. Finally, studies are being performed, using stable surrogates, to quantify the efficiency of producing neutral atomic beams from rare isotopes harvested from the water beam dump at the Facility for Rare Isotope Beams, which will provide a new, abundant source of Ra-225 atoms.   

Intrinsic shape and low-lying collective states of atomic nuclei within the self-consistent mean-field framework

Experiments with atoms or molecules containing nuclei that possess octupole deformation may improve substantially the limits on time reversal violation. Within the spherical self-consistent mean-field framework, we establish a profound connection between the intrinsic shape of nuclei and the dynamics exhibited by their low-lying collective states. Our investigation spans the nuclide chart, offering a comprehensive exploration of nuclear deformations, encompassing quadrupole, octupole, and hexadecapole patterns. Emphasizing the role of the shell-driving mechanism, our research sheds light on the evolutionary aspects of nuclear deformation.