Development of a guide system for free neutron oscillation searches at the European Spallation Source

Abstract: In this project, a neutron delivery system for the study of free neutron oscillations at the HIBEAM beamline at the European Spallation Source (ESS) has been developed. The HIBEAM experiment is part of a two-stage program at ESS which will address open questions in physics; specifically the nature of dark matter and the observed asymmetry between matter and antimatter in the Universe. This will be done through high-sensitivity searches for hypothetical free neutron oscillations to antineutrons and sterile neutrons, the latter being a candidate for dark matter. These oscillation processes violate baryon number conservation and so their observation could help explain the matter-antimatter asymmetry. The primary focus of this thesis was the development of a guide system for the search for neutron to antineutron oscillations. A few different guiding systems were tried out and optimized, with the best performing setup consisting of an elliptic guide in the so called monolith and a 20 m long second elliptic guide which was constructed as an extension of the first one. It was shown that with this optimized setup at the HIBEAM beamline, an increased sensitivity for free neutron to antineutron conversion searches compared to previous experiments can be obtained. A guide system for neutron to sterile neutron searches was also developed. Two setups were tried in this case, which consisted of a curved guide together with two different monolith guides. Both guide systems are shown to be viable options for a search for sterile neutrons in their current state, however they could also function as a base for further optimization.