Characterization of PSI nEDM apparatus: T1, T*2, and UCN storage lifetime

Abstract

The neutron electric dipole moment (nEDM) experiment, located at the Paul Scherrer Institute (PSI), employs the Ramsey technique of separated oscillating fields, at room temperature, to search for a permanent EDM in the neutron. Neutrons with very low energy are produced in the PSI ultracold neutron (UCN) source, which are polarized by allowing them to pass through a 5 T strong magnetic field produced by a superconducting magnet. The UCNs are then stored in a chamber, where they are subject to the Ramsey technique. Manipulation of magnetization of the ensemble of stored UCNs is governed by Bloch equations, which describe the Larmor precession under the influence of a magnetic field, and involve two channels of depolarization; the transverse depolarization and the longitudinal depolarization. The time constants for longitudinal and transverse depolarization, T1 and T*2, respectively, were measured in the PSI nEDM apparatus at the beginning of the nEDM data taking schedule. T1 and T*2 play an important role in optimizing the period of free spin-precession in the Ramsey technique. We report the relaxation time constants as T1=(5770\pm420) s and T*2=(1550\pm22) s, for the UCNs from the PSI UCN source in the PSI nEDM apparatus. These values of T1 and T*2 are consistent with values reported in EPJ Web Conf. 219, 02001 (2019).