Description of recent large-$q$ neutron inclusive scattering data from liquid $^4$He

TL;DR

This paper presents dynamical calculations of large-$q$ structure functions for liquid $^4$He at low temperatures, comparing with recent experimental data, and investigates the asymptotic behavior and extraction of physical parameters.

Contribution

It extends theoretical calculations of liquid $^4$He structure functions beyond experimental q-range and critically examines the extraction of physical parameters from data.

Findings

Small deviations from $1/q$ behavior for smooth potentials

Confirmation of the asymptotic approach of the response

Doubt cast on the extraction of Final State Interaction parameters

Abstract

We report dynamical calculations for large-$q$ structure functions of liquid $^4$He at $T$=1.6 and 2.3 K and compare those with recent MARI data. We extend those calculations far beyond the experimental range $q\le 29\Ain$ in order to study the approach of the response to its asymptotic limit for a system with interactions having a strong short-range repulsion. We find only small deviations from theoretical $1/q$ behavior, valid for smooth $V$. We repeat an extraction by Glyde et al of cumulant coefficients from data. We argue that fits determine the single atom momentum distribution, but express doubt as to the extraction of meaningful Final State Interaction parameters.