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

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 reported a large discrepancy of neutron lifetime with the current particle data value. Our partial reanalysis suggests the possibility of systematic effects that were not included in this publication.

Quasielastic scattering in the interaction of ultracold neutrons with a liquid wall and application in a reanalysis of the Mambo I neutron-lifetime experiment

“…The analysis is very similar to our previous second-order treatment [12] of UCN scattering and loss at a wall with static, rather than dynamic, roughness. The transition from static to dynamic roughness is essentially accomplished by replacing the Fourier transform F (q) of the static height-height correlation in Ref.…”

“…For structure factors with exponential decay, as often used for static roughness, as in Ref. [12], no divergence problem is encountered. It is common practice in experiments on capillary waves, as in Ref.…”

“…Since the correspondence in the derivations is almost one-to-one, we will mainly present and apply the final results, referring to Ref. [12] for intermediary steps.…”

“…The transition from static to dynamic roughness is essentially accomplished by replacing the Fourier transform F (q) of the static height-height correlation in Ref. [12] (see, e.g., the comprehensive review [13], for further details) by the dynamical structure factor S(q, ω) and replacing integrations over q by integrals over q and ω. Since the correspondence in the derivations is almost one-to-one, we will mainly present and apply the final results, referring to Ref.…”

“…[12], I (00) = |R i | 2 is the specular reflectivity, calculated for the given η > 0; I (11) is the intensity per unit of solid angle and energy quasielastically scattered into the vacuum, calculated for η = 0;…”