Experiments of Search for Neutron Electric Dipole Moment and Spin-Dependent Short-Range Force
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It is of great importance to identify new sources of discrete symmetry violations because it can explain the baryon number asymmetry of our universe and also test the validity of various models beyond the standard model. Neutron Electric Dipole Moment (nEDM) and short-range force are such candidates for the new sources of P&T violations. A new generation nEDM experiment was proposed in USA in 2002, aiming at improving the current nEDM upperlimit by two orders of magnitude. Polarized <super>3</super>He is crucial in this experiment and Duke is responsible for the <super>3</super>He injection, measurements of <super>3</super>He nuclear magnetic resonance (NMR) signal and some physics properties related to polarized <super>3</super>He.
A Monte-Carlo simulation is used to simulate the entire <super>3</super>He injection process in order to study whether polarized <super>3</super>He can be successfully delivered to the measurement cell. Our simulation result shows that it is achievable to maintain more than 95% polarization after <super>3</super>He atoms travel through very complicated paths in the presence of non-uniform magnetic fiels.
We also built an apparatus to demonstrate that the <super>3</super>He precession signal can be measured under the nEDM experimental conditions using the Superconducting Quantum Interference Device (SQUID). Based on the measurement result in our lab, we project that the signal-to-noise ratio in the nEDM experiment will be at least 10.
During this SQUID test, two interesting phenomena were discovered. One is the pressure dependence of the T1 of the polarized <super>3</super>He which has never been reported before. The other is the discrepancy between the theoretically predicted T2 and the experimentally measured T2 of the <super>3</super>He precession signal. To investigate these two interesting phenomena, two dedicated experiments were built, and two papers have been published in Physical Review A.
In addition to the nEDM experiment, polarized <super>3</super>He is also used in the search for the exotic short-range force. The high pressure <super>3</super>He cell used in this experiment has a very thin window (~250 μm) to maximize the effect from the force. We demonstrate that our new method could improve the current best experimental limit by two orders of magnitude. A rapid communication demonstrating the technique and the result was published in Physical Review D.
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