[Zurück]

C. Klauser:
"High Precision Neutron Polarization For PERC";
Betreuer/in(nen), Begutachter/in(nen): H. Abele, K. Kirch; Atominstitut TU Wien, 2013; Rigorosum: 20.11.2013.

The decay of the free neutron into a proton, an electron and an anti-electron neutrino offers a simple system to study the semi-leptonic weak decay. High precision measurements of angular correlation coefficients of this decay provide the opportunity to test the standard model on the low energy frontier.
The Proton Electron Radiation Channel PERC is part of a new generation of expriments pushing the accuracy of such an angular correlation coefficient measurement towards 10$^{-4}$. Past experiments have been limited to an accuracy of 10$^{-3}$ with uncertainties on the neutron polarization as one of the leading systematic errors. This thesis focuses on the development of a stable, highly precise neutron polarization for a large, divergent cold neutron beam. A diagnostic tool that provides polarization higher than 99.99 \% and analyzes with an accuracy of 10$^{-4}$, the Opaque Test Bench, is presented and validated. It consists of two highly opaque polarized helium cells.
The Opaque Test Bench reveals depolarizing effects in polarizing supermirrors commonly used for polarization in neutron decay experiments. These effects are investigated in detail. They are due to imperfect lateral magnetization in supermirror layers and can be minimized by significantly increased magnetizing fields and low incidence angle and supermirror factor m. A subsequent test in the crossed (X-SM) geometry demonstrated polarizations up to 99.97\% from supermirrors only, improving neutron polarization with supermirrors by an order of magnitude.
The thesis also discusses other neutron optical components of the PERC beamline: Monte-Carlo simulations of the beamline under consideration of the primary guide are carried out. In addition, calculation shows that PERC would statistically profit from an installation at the European Spallation source. Furthermore, beamline components were tested. A radio-frequency spin flipper was confirmed to work with an efficiency higher than 0.9999.