Data and systematic error analysis for the neutron electric dipole moment experiment at the Paul Scherrer Institute\ud and Search for Axionlike Dark Matter

This thesis details work conducted as part of the experimental collaboration responsible for the neutron electric dipole moment (nEDM) experiment based at the Paul Scherrer Institute (PSI). The nEDM is a sensitive probe of a broad range of new CP violating physics beyond the standard model, however it remains elusive: while historic experiments since 1951 have increased in sensitivity by over six orders of magnitude, a nonzero nEDM is yet to be detected. Many theories of physics beyond the standard model predict neutron EDMs of a size that would be detectable by current and next generation experiments, and it has been said that measurements of the neutron EDM have ruled out more theories than any other experiment. One explanation of the smallness of the neutron EDM, the Peccei-Quinn theory, invokes a novel particle, the axion, which is also a credible dark matter candidate. The axion is yet to be detected.\ud \ud The work covers three main areas. First, contributions to the data analysis technique used to analyse the main dataset to produce a new world-leading limit on the neutron EDM. Second, an auxiliary measurement campaign to map the magnetic field within the experiment's magnetic shields is described, and the analysis of these datasets to provide corrections for several critical systematic effects is presented. Finally, a novel analysis of the data taken at a previous-generation nEDM experiment is used to derive the first experimental limits on the coupling of axion-like dark matter particles to gluons is described. These exclusions are up to 1000 times stronger than previous results for cosmologically interesting 10-22 eV axions.