Stored Ultracold Neutron Lifetime Experiments: Non-Inertial Frame Effects on the Neutron Velocity Spectrum

TL;DR

This paper investigates how Earth's rotation influences ultracold neutron spectra in storage experiments, revealing small but significant non-inertial effects that could impact high-precision measurements.

Contribution

It introduces a model for non-inertial frame effects on UCN velocity spectra in rotating storage cells, highlighting their importance for future high-accuracy experiments.

Findings

Non-inertial effects cause spectrum broadening.

Effects induce a random walk in neutron momentum.

Impacts are relevant for precision UCN experiments.

Abstract

Ultracold neutrons (UCN), stored in a cell with hard walls that is attached to, and therefore rotating with, the Earth, will experience non-inertial frame effects, resulting in a broadening of the UCN spectrum. A heating or cooling of the spectrum is also possible. This is because the stored UCN are in a freely falling (inertial) frame between sudden wall collisions, and the acceleration of the cell relative to this frame means that the cell walls will have a new quasi-random velocities between subsequent UCN wall collisions. This results in a random walk of UCN trajectories in momentum space. Estimates of the effects on UCN with specified initial velocities are presented. Although the effects appear as small, they are worth considering for experiments of current interest, and will be important for possible future experiments with anticipated improved accuracy.