Neutron supermirrors (SMs) are a crucial part of many scattering and particle physics experiments. So far, Ni(Mo)/Ti SMs have been used in experiments that require to transport a polarized neutron beam due to their lower saturation magnetization compared to Ni/Ti SMs. However, next generation β decay experiments require SMs that depolarize below 10−4 per reflection to reach their targeted precision. The depolarization of a polarized neutron beam due to reflection from Ni(Mo)/Ti SMs has not yet been measured to that precision. Recently developed Cu/Ti SMs with a very low saturation magnetization compared to Ni(Mo)/Ti may serve as an alternative. In this paper, we test the performance of both mirrors. At a first stage, we present four-states polarized neutron reflectivity (PNR) curves of Ni(Mo) and Cu monolayers measured at the neutron reflectometer SuperADAM and perform a full polarization analysis, showing a difference between the magnetic scattering length density (mSLD) of both materials, with Cu having a lower mSLD than Ni(Mo). These results are corroborated with the full polarization analysis of four-states PNR curves of m=2 Ni(Mo)/Ti and Cu/Ti SMs. In a second stage, we measured the depolarization (D) that a polarized neutron beam suffers after reflection from the same Ni(Mo)/Ti and Cu/Ti SMs by using the Opaque Test Bench setup. We find upper limits for the depolarization of DCu/Ti(4N5)<7.6×10−5, DNi(Mo)/Ti<8.5×10−5, and DCu/Ti(2N6)<6.0×10−5 at the 1σ confidence level, where (4N5) corresponds to a Ti purity of 99.995% and (2N6) to 99.6%. The uncertainties are statistical. These results show that all three SMs are suitable for being used in next generation β decay experiments. We found no noticeable dependence of D on the q value or the magnetizing field, in which the samples were placed.
@article{arxiv.2503.22561,
title = {Depolarization studies on low-depolarizing Cu/Ti and Ni(Mo)/Ti neutron supermirrors},
author = {Jose Manuel Gómez-Guzmán and Karina Bernert and Anton Devishvili and Christine Klauser and Bastian Märkisch and Ulrich Schmidt and Torsten Soldner},
journal= {arXiv preprint arXiv:2503.22561},
year = {2025}
}