Surface roughness effect on ultracold neutron interaction with a wall and implications for computer simulations

TL;DR

This paper investigates how surface roughness affects ultracold neutron reflection and loss, revealing a counterintuitive reduction in loss with roughness and exploring implications for neutron lifetime experiments.

Contribution

It provides a review of diffuse scattering and loss coefficients, reports a surprising reduction in loss due to roughness, and discusses transitioning from quantum to ray optics in simulations.

Findings

Roughness can reduce neutron loss coefficients unexpectedly.

Simulation suggests potential systematic effects in neutron lifetime measurements.

Transition from quantum to ray optics may influence neutron-surface interaction modeling.

Abstract

We review the diffuse scattering and the loss coefficient in ultracold neutron reflection from slightly rough surfaces, report a surprising reduction in loss coefficient due to roughness, and discuss the possibility of transition from quantum treatment to ray optics. The results are used in a computer simulation of neutron storage in a recent neutron lifetime experiment that re-ported a large discrepancy of neutron lifetime with the current particle data value. Our partial re-analysis suggests the possibility of systematic effects that were not included in this publication.