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

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.