Title: Simulation Study for Systematic Uncertainty Suppression in nEDM Experiment Assuming Various Surfaces Roughness
Abstract: The neutron intrinsic electric dipole moment (nEDM) can be measured as the ultracold neutron (UCN) spin precession in a storage container under homogeneous electric and magnetic fields.In the experiments, when UCNs are in a certain ordered motion, systematic uncertainties due to the relativistic magnetic field connected with a longitudinal magnetic field gradient in the storage container are enhanced, and could be comparable to the expected nEDM.They are associated with various complex factors such as the inhomogeneity of the magnetic field, the geometrical configuration of storage volume, and its surfaces roughness.Therefore, a simulation study is essential to evaluate these complex systematic effects.Non-specular reflection that occurs at the sidewalls of the storage volume because of the surfaces roughness can suppress the systematic uncertainties effectively.We developed Geant4UCN using a micro-roughness model formulated by Steyerl [1].In this study, we calculated the spin phase shift in the situation that UCNs rotate clockwise or counterclockwise in the cylindrical volume with surfaces roughness of 0.7 nm and 2.1 nm, correlation length of 22 nm and 45 nm, electric and magnetic fields of 10 kV/cm and 1 µT, respectively, and a storage time of 100 s.This calculation took into consideration the non-specular reflections induced by rough surfaces that randomize ordered motions of UCNs.Therefore, this simulation allow us to understand how effectively surfaces roughness suppresses systematic uncertainties.Further, we report the results obtained from the analysis.