Session G13: Fundamental Symmetries II

Live

The Baryon Asymmetry of the Universe (BAU) requires charge-parity (CP) violating physical processes. The predicted values of electric dipole moments (EDM) and Magnetic quadrupole moments (MQM) calculated from the Standard Model (SM) is insufficient to explain the observed BAU. These moments are enhanced significantly in a deformed nuclei. The nuclear MQM is free from the Schiff shielding. Hence, in this work, we will be presenting the survey result of a list of candidate deformed nuclei for nuclear MQM measurement and their contribution to atomic EDM.   

Live

A major deficiency of the Standard Model is its inability to explain the observed asymmetry between matter and antimatter. Toward a resolution of this problem, Andrei Sakharov proposed three conditions for a theory to produce a matter-dominated universe, in particular a violation of the combined charge-parity (CP) symmetry. The measurement of a neutron electric dipole moment may provide a path to study beyond-the-Standard-Model sources of CP violation. The only available nonperturbative approach is lattice QCD (LQCD). Unfortunately the mixing of the underlying operators is natively parametrized by the lattice spacing alone, and the continuum limit is muddled by power divergences. We use the gradient flow to circumvent this problem. The flow fixes QCD as the initial condition for a set of diffusive PDEs in a parameter called the flow time such that the high-momentum modes of the fields are suppressed. Further, this provides an alternative parametrization of the mixing, and the continuum limit may be performed smoothly. We herein discuss the case of the quark chromoelectric dipole moment (qCEDM). We present novel perturbative calculations of its leading-order mixing and compare to flowed LQCD computations.   

Live

The nEDM@SNS experiment aims to increase experimental sensitivity to hadronic CP violation by nearly two orders of magnitude. The experiment will use polarized He-3 both as a co-magnetometer and to analyze the neutron spin in-situ during precession. Polarized He-3 from an atomic beam source will be injected into the superfluid liquid helium and diffuse into the measurement cell. I will present a system of recycled coils from the NPDGamma and n-3He experiments to test the injection cell with polarized He-3 from a metastability-exchange optical polarizer. The system includes a symmetric 5-loop gradient coil at both ends to actively tune out first-order gradients.   

Live

The neutron electric dipole moment experiment at the Spallation Neutron Source (nEDM@SNS) will implement a novel method, which utilizes polarized ultra-cold neutrons (UCN) and polarized $^3$He in a bath of superfluid $^4$He, to place a new limit on the nEDM down to 2-3×10$^{−28}$ e·cm. The experiment will employ a cryogenic magnet and magnetic shielding package to provide the required magnetic field environment to achieve the proposed sensitivity. This talk will describe the design and implementation of $^3$He polarimetry setup at the SNS to measure the neutron polarization and transmission losses resulting from passage through the magnetic shielding and cryogenic windows.   

Live

The neutron electric dipole moment experiment at the Spallation Neutron Source (nEDM@SNS) proposes to measure the nEDM using the spin-dependent capture cross section of neutrons on helium-3. The critical dressing mode of this experiment uses an oscillating magnetic field to dress the gyromagnetic ratios of neutrons and helium-3 to the same value. While this technique grants increased sensitivity to the nEDM by improving the signal-to-noise ratio, this mode of measurement also introduces additional noise from the power supply used to drive the dressing field. This can lead to randomly fluctuating magnetic fields which cause the spins of neutrons and helium-3 to drift apart over time. Here we use second-order time-dependent perturbation theory to compute relaxation and frequency shifts due to power supply noise in terms of the noise power spectrum, and compare these calculations to numerical solutions obtained by integrating the Bloch equations.   

Live

The Neutron Optics Parity and Time Reversal EXperiment (NOPTREX) aims to search for possible parity and time reversal invariance violation in the $\sigma_n \cdot k_n \times I$ dependence of the low-energy neutron-nucleon forward scattering amplitude. Certain nuclei such as $^{139}La$ have been shown to exhibit amplification of up to $10^6$, providing experimental sensitivity at the level of the next generation of searches for the electric dipole moment of the neutron. I will report on world-wide measurements of parity violating amplitudes and the so-called $\kappa$ factor of various target nuclei, which determine the experimental sensitivity, and also on the development of neutron polarizers, polarized targets, and detectors for this experiment.   

Live

We will investigate T violation in neutron interactions with heavy nuclei at a compound nuclear p-wave resonance by searching for a P-odd and T-odd term in the neutron forward scattering amplitude. Thew 131Xe P-odd effects have already been measured, however the previously unmeasured neutron incoherent scattering length of the polarized 131Xe target, would be a large systematic error because of the resulting pseudomagnetic precession. Measurement of this incoherent neutron scattering length requires absolute polarimetry of 131Xe. Here neutrons provide us a method for NMR calibration using hyperpolarized 3He as the standard instead of the more typical thermally polarized 1H sample. Since the 3He polarization dependent neutron absorption cross section is accurately known, measurement of neutron absorption of the polarized 3He gives an absolute NMR calibration. The absolute 131Xe polarimetry/magnetization used to determine the neutron incoherent scattering length of 131Xe as measured from its pseudomagnetic precession observed in measurements on the JNSE instrument at the FRMII is discussed [1]. [1] Heinz Maier-Leibnitz Zentrum. (2015). J-NSE: Neutron spin echo spectrometer. Journal of large-scale research facilies, 1, A11. http://dx.doi.org/10.17815/jlsf-1-34   

Live

Spin-dependent amplitudes in polarized neutron-polarized nucleus forward scattering can cause systematic errors in NOPTREX. We performed the first measurement of neutron pseudomagnetic precession\footnote{Zimmer, O., Ehlers, G., Farago, B. et al. A precise measurement of the spin-dependent neutron scattering length of 3He. EPJ direct 4, 1–28 (2002). https://doi.org/10.1007/s1010502a0001} in neutron transmission through polarized $^{131}$Xe and $^{129}$Xe with the J-NSE Neutron Spin Echo spectrometer at FRM II reactor facility in Germany\footnote{Heinz Maier-Leibnitz Zentrum. (2015). J-NSE: Neutron spin echo(NSE) spectrometer. Journal of large-scale research facilities, 1, A11. http://dx.doi.org/10.17815/jlsrf-1-34}. The Xenon nuclei were polarized using an in-situ Spin Exchange Optical Pumping system. We extracted pseudomagnetic precession angles from phase-sensitive NSE signals and then calculated the corresponding incoherent scattering lengths. We will present the experimental setup of the polarized Xenon pseudomagnetic precession measurement, the data analysis procedure, the result and its implication.   

On Demand

Many fundamental symmetry experiments, such as measurements of static electrodynamic moments or neutron spin rotation depend on experimentalists' ability to tightly control the magnetic fields within their apparatus. One source of error in such experiments is transient magnetic fields that have not been effectively shielded. To minimize this error we propose surrounding the measurement volume of the apparatus with a superconducting mesh in order to freeze in the desired fields. The practical limits of this method and potential gains to error reduction will be discussed.