The precise knowledge of the neutron polarization is needed in tests of the electroweak Standard Model using angular correlations in polarized neutron beta decay. We performed an experimental comparison study of two different methods of polarization analysis of a cold neutron beam which are based on spin-dependent reflection, respectively, transmission. The compared devices are a supermirror analyzer used in prior neutron decay studies and an opaque transmission spin filter of either polarized 3He or polarized protons. The results of the neutron polarization measured with the supermirror analyzer and with the spin filter coincided in three different experiments within 0.1-0.2%.
Zimmer, O., Hautle, P., Heil, W., Hofmann, D., Humblot, H., Krasnoschekova, I., … Vassilev, A. (2000). Spin filters and supermirrors: A comparison study of two methods of high-precision neutron polarization analysis. Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 440(3), 764–771. https://doi.org/10.1016/S0168-9002(99)01080-3