Session C01: Tests of Fundamental Symmetries and Searches for New Interactions

Weak Decay Recoil Spectroscopy with Superconducting and Optomechanical Sensors

Nuclear beta and electron capture (EC) decay serve as sensitive probes of the structure and symmetries of the charged weak force between quarks and leptons. As such, precision measurements of the final-state products in these processes can be used as powerful laboratories to search for new physics from the meV to TeV scale. Significant advances in rare isotope availability and quality, coupled with decades of sensing technique development from the AMO community have led us into a new era of fundamental tests of nature using unstable nuclei. For the past few years, we have taken the approach of embedding radioisotopes in thin-film superconducting tunnel junctions (STJs) to precisely measure the recoiling atom that gets an eV-scale "kick" from the neutrino following EC decay. Since these recoils are encoded with the fundamental quantum information of the decay process, they can also carry unique signatures of weakly coupled beyond standard model (BSM) physics; including neutrino mass, exotic weak currents, and potential "dark" particles created within the Q-value window of the decay. These measurements provide a complimentary and (crucially) model-independent portal to the dark sector with sensitivities that push towards synergy between laboratory and cosmological probes. Ongoing and future work in this field include extending the physics reach of recoil experiments with STJs using "on-line" measurements of short-lived systems at FRIB, as well as using macroscopic amounts of harvested rare isotopes in optically levitated nanospheres for direct momentum measurements of the decay recoils.   

Testing Lorentz Invariance in Weak Decay Experiments

Violating the Lorentz invariance attracts theoretical interests, especially for building quantum gravitational theories. Also, it has been experimentally tested in many sectors; however, the testing precisions in the weak interaction are an order of magnitude worse than other interactions, e.g., electromagnetic interaction, etc. After trying to test lifetime variation synchronizing to the Earth's rotation of polarized Li-8 at TRIUMF, we performed a new experiment testing that of muon at J-PARC aiming 10-ppm precision. The status of the experiment and new technical developments to perform high statistics measurements will be presented.   

Searching for Time-Reversal Violation Using Pear-Shaped Nuclei in the FRIB Era

Experimental tests of fundamental symmetries using nuclei and other particles subject to the strong nuclear force have led to the discovery of parity (P) violation and the discovery of charge-parity (CP) violation. It is believed that additional sources of CP-violation may be needed to explain the apparent scarcity of antimatter in the observable universe. A particularly sensitive and unambiguous signature of time-reversal- (T), parity-, and CP-violation (via the CPT theorem) would be the existence of an electric dipole moment (EDM). The next generation of EDM searches in a variety of complimentary systems (neutrons, atoms, and molecules) will have unprecedented sensitivity to physics beyond the Standard Model. This talk will focus on current and planned experiments that use radioactive isotopes with pear-shaped nuclei. This uncommon nuclear structure significantly amplifies the observable effect of symmetry violations originating within the nuclear medium when compared to isotopes with relatively undeformed nuclei such as Mercury-199. Certain isotopes of Radium (Ra) and Protactinium (Pa) are both expected to have greatly enhanced sensitivity to symmetry violations and will be produced in abundance at the Facility for Rare Isotope Beams currently operating at Michigan State University. I will describe the current status of the ongoing search for the atomic EDM of Ra using laser cooling and trapping techniques as well as the prospects for next generation searches for time-reversal violation possibly using radioactive molecules to further enhance the new physics sensitivity in the FRIB-era.   

Fundamental Physics with Cold Radioactive Heavy Elements

The electric dipole moment (EDM) for an elementary particle can be used to study physics beyond the Standard Model. A non-zero EDM leads to CP violation, which is important for understanding the mater-antimatter asymmetry in the Universe. In heavy paramagnetic atoms, due to relativistic effects, the electron EDM results in an atomic EDM that is enhanced by a factor equal to the 3rd power of the nuclear charge. The heaviest alkali element francium (Fr) has the largest enhancementof about 895. At present, the construction of a high-intensity laser-cooled Fr beam line at RIKEN is almost ready. The development to measure the EDM by atomic interferometry with an accuracy of 10^-29 ecm is in progress. In this experiment, we will use quantum optics techniques such as laser cooling and trapping in an optical lattice to achieve longer interaction times and better use of radioactive atoms. Low-energy Fr ions will be produced by nuclear fusion evaporation reactions, and they will be neutralized by depositing them on a suitable neutralizing element. Then Fr atoms are rapidly decelerated and trapped by laser cooling in a magneto-optical trap (MOT). They will then be transferred to an optical lattice to measure the spin precession of the Fr with the Ramsey resonance method. 

Furthermore, we are developing the new quantum sensing technique using ultracold entangled Fr states in an optical lattice. The dependence of the uncertainty in the EDM on a single-photon Rabi frequency inside the optical cavity is investigated. The quantum sensing using the spin squeezed state of a Fr atom for the measurement of its EDM is predicted to offer an uncertainty below the standard quantum limit, which means the measurement accuracy of the EDM at a level below 10⁻³⁰ ecm.  The Fr trapped in the optical lattice can be also used to detect the parity non-conservation in the atomic system to study the weak interaction in the quantum many-body system. The status of the fundamental physics using cold Fr source is presented in this paper.