Technical Developments in the Search for a Short-Range Spin-Dependent Fifth Force Interaction

Theoretical treatments of the possible interactions between two fermions from boson exchange in the nonrelativistic limit\footnote{B. Dobrescu and I. Mocioiu, J. High Energ. Phys. 2006.11 (2006): 005.} include a short-range monopole-dipole interaction proportional to $\vec{S} \cdot \vec{r}$. This potential would generate an NMR frequency shift in an ensemble of polarized nuclei when an unpolarized mass is brought nearby.\footnote{M. Bulatowicz et al, Phys. Rev. Lett. 111, 102001 (2013).}$^,$\footnote{P.-H. Chu et al, Phys. Rev. D 87, 011105(R) (2013).} Techniques to move the mass as close to the polarized nuclei as possible are needed to access sub-millimeter interaction ranges. We describe the preparation of nonmagnetic test masses and a mechanical system to bring the test mass close to an ensemble of polarized $^{3}$He nuclei, which are polarized in a spin-exchange optical pumping cell at Duke University. We describe how the masses are prepared to conform to the slightly asymmetric contours of the 100-micron thick glass cell window by a combination of coordinate measuring machine data and a spring-loaded suspension system that allows the mass to slightly rotate.