  Trapped ultracold neutrons (UCN) have for many years been the mainstay of
experiments to search for the electric dipole moment (EDM) of the neutron, a
critical parameter in constraining scenarios of new physics beyond the Standard
Model. Because their energies are so low, UCN preferentially populate the lower
region of their physical enclosure, and do not sample uniformly the ambient
magnetic field throughout the storage volume. This leads to a substantial
increase in the rate of depolarization, as well as to shifts in the measured
frequency of the stored neutrons. Consequences for EDM measurements are
discussed.
