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C. Klauser, T. Bigault, P. Böni, P. Guimera Millan, M. Schneider, T. Soldner:
"High Precision Neutron Polarisation with Supermirrors";
Vortrag: DPG spring meeting 2013 (Hadronic and Nuclear Physics), Dresden; 04.03.2013 - 08.03.2013.

Absolute measurements of correlation coefficients in neutron beta decay are presently limited to a relative accuracy in the order of 10−3 by systematics and statistics. Next-generation instruments aim for 10−4 accuracy, implying a 10−4 accuracy for the polarization of a large cold neutron beam. State-of-the-art polarizing super mirrors in the X-SM geometry deliver about 99.7% polarization only. This limitation of the performance is caused by depolarization by the supermirrors themselves. We present a systematic study of depolarizing effects in polarizing supermirrors. The highly sensitive Opaque Test Bench based on 3He spin filters is used as diagnostic tool. We have studied depolarization in both reflection and transmission for different supermirrors, varying in material and supermirror factor m, and investigated the relationship to magnetizing field, incidence angle and wavelength. The results of this study have been used to push the polarisation of the X-SM geometry to 99.970(3), combining a FeSi mirror and a CoTi bender.