[Journal of the Physical Society of Japan Proceedings of the 14th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU2016) - Kyoto, Japan (July 25-30, 2016)] Proceedings of the 14th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU2016) - \(\eta \) n Scattering Length from the \(\gamma \) d \( \to \) p \(\eta \) n Reaction at \(E_{\gamma } \sim 0.9\) GeV