Gravitationally enhanced depolarization of ultracold neutrons in magnetic field gradients, and implications for neutron electric dipole moment measurements

TL;DR

This paper investigates how gravitational effects cause increased depolarization of ultracold neutrons in magnetic field gradients, impacting the precision of neutron EDM experiments and highlighting the importance of accounting for these effects.

Contribution

It introduces the concept of gravitationally enhanced depolarization in UCN experiments and discusses its implications for neutron EDM measurement accuracy.

Findings

Gravitational effects significantly increase depolarization rates.

Depolarization leads to shifts in measured neutron precession frequencies.

Implications for improving neutron EDM experimental designs.

Abstract

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.