Spin flip loss in magnetic storage of ultracold neutrons

TL;DR

This paper investigates how lateral motion in magnetic traps causes depolarization of ultracold neutrons, impacting precision neutron lifetime measurements, using an approximate quantum mechanical approach that considers non-vertical neutron trajectories.

Contribution

It extends previous models by analyzing depolarization effects for non-vertical neutron motions in magnetic storage, highlighting lateral motion as the main depolarization source.

Findings

Lateral neutron motion significantly increases depolarization loss.

Depolarization is primarily caused by lateral, not vertical, motion.

The analysis applies to both existing and proposed magnetic storage experiments.

Abstract

We analyze the depolarization of ultracold neutrons confined in a magnetic field configuration similar to those used in existing or proposed magneto-gravitational storage experiments aiming at a precise measurement of the neutron lifetime. We use an approximate quantum mechanical analysis such as pioneered by Walstrom \emph{et al} [Nucl. Instrum. Methods Phys. Res. A 599, 82 (2009)]. Our analysis is not restricted to purely vertical modes of neutron motion. The lateral motion is shown to cause the predominant depolarization loss in a magnetic storage trap.