Magnetic fields and ultracold neutron production: studies towards the neutron electric dipole moment experiment at TRIUMF

Abstract

The existence of a non-zero neutron electric dipole moment (nEDM) confirms the theoretical models of Physics beyond the Standard Model which provide extra sources of CP violation. Based on Sakharov Criteria, CP violation is one of the main ingredients to create the baryon asymmetry in the universe. The current upper limit of the neutron EDM was found to be 3.0×10^(−26) e·cm, which is below the theoretical models predictions. As a result, there is a worldwide quest to find a finite nEDM. The typical experimental method to measure the nEDM uses the ultracold neutrons (UCN) and employs the Ramsey method of separated oscillatory fields. In this method, the Larmor precession frequency of UCN is measured in the presence of aligned Electric and Magnetic fields orientations. Such precision measurements require high UCN statistics and very stable and homogeneous magnetic fields. The work presented in this thesis is focused on the magnetic field and UCN studies for the future nEDM measurement at TRIUMF.

The TUCAN (TRIUMF UltraCold Advanced Neutron source) collaboration’s goal is to measure the nEDM to the sensitivity level of 10^(−27) . For this measurement, the < 1 pT magnetic stability requirement could be met by using magnetic shields with high magnetic permeability (μ) to reduce the external magnetic fields. However, external sources such as ambient temperature fluctuations could give rise to a change in the magnetic properties such as μ. The result of the temperature dependence of μ measurements and related simulations are presented here. These measurements set a limit on the temperature control level for the future nEDM measurement at TRIUMF.

The TUCAN collaboration’s goal is to design a next-generation UCN source to increase the UCN statistics and reach the required nEDM sensitivity. In 2016, the vertical UCN source that was previously developed at RCNP was shipped to TRIUMF. In 2017, we significantly improved the control system for data acquisition and conduced the first UCN experiments.The status of the current UCN facility at TRIUMF and the result of the first UCN production tests are presented here.