Measuring the Spin-Dependent Scattering Length of $^{3}$He using Neutron Interferometry

Experimental measurements of neutron scattering lengths are only recently achieving the required accuracy to test nucleon-nucleon (N-N) models. Neutron Interferometry (NI) provides some of the most precise values of spin-independent neutron scattering lengths including percent or better measurements for n-H, n-D, and n-$^{3}$He. For $^{3}$He, the spin-dependent neutron scattering length, b$_{i}$, has been measured once before by Zimmer \textit{et al}. [1] using a polarized $^{3}$He target inside a spin echo apparatus. Their result b$_{i}=-$2.365(20) differs from various theoretical models by more than 4$\sigma $. Currently, we are conducting an experiment to measure b$_{i}$ for $^{3}$He to better than half a percent at the NI and Optics Facility at the National Institute of Standards and Technology (NIST) using a small, flat-windowed gas cell containing polarized $^{3}$He. This is the first use of a polarized gas target in a NI. Results from this experiment will be presented. This work is supported by the National Science Foundation and NIST. \newline \newline [1] O. Zimmer \textit{et al}. Journal EPJ direct, 4(1):1--28, 2002.