A Metastability-Exchange Optical Pumping and Compression System using Polarized $^{3}$He for a Proposed Laboratory Search for Neutron Monopole-Dipole Interactions

$^{3}$He nuclei polarized using the metastability-exchange optical pumping (MEOP) method have been used for scientific applications such as magnetometry in space, neutron polarization and analysis, and medical imaging. In this talk we explain how this technique is also well-suited for a proposed experiment [1] to search for possible monopole-dipole interactions of polarized $^{3}$He nuclei with matter. The P-odd and T-odd monopole-dipole potential proposed by Moody and Wilczek [2] is proportional to $\vec{s} \cdot \vec{r}$ where $\vec{s}$ is the $^{3}$He spin and $\vec{r}$ is the separation between the particles. It can be induced by axions, and ARIADNE proposes to perform NMR on a polarized $^{3}$He ensemble at 4K with a radially-slotted tungsten disk spinning at a multiple of the $^{3}$He Larmour frequency to induce a resonant monopole-dipole perturbation. The radial slot length variations are chosen to maximize sensitivity to a monopole-dipole interaction range corresponding to the axion window. We describe the advantages that MEOP presents for this experiment and describe the MEOP-based polarized $^{3}$He gas compression system at Indiana University [3].\\[4pt] [1] A. Arvanitaki, A Geraci, PRL 113 161801 (2014)\\[0pt] [2] J. Moody, F Wilczek, PRD 30 130\\[0pt] [3] D. Hussey et al, RSI 76, 053503 (2005