Energy dependence of non-local potentials

TL;DR

This study revisits phenomenological non-local optical potentials for neutron elastic scattering, demonstrating that an energy-dependent imaginary component improves data fitting across multiple nuclei and energies.

Contribution

Introduces energy and asymmetry dependencies into non-local optical potentials, providing improved global parameterizations for neutron scattering data.

Findings

Energy dependence in the imaginary potential is essential for accurate data description.

Two new parameterizations outperform original potentials for fitted and non-fitted nuclei.

Non-locality alone does not eliminate the need for energy dependence in optical potentials.

Abstract

Recently a variety of studies have shown the importance of including non-locality in the description of reactions. The goal of this work is to revisit the phenomenological approach to determining non-local optical potentials from elastic scattering. We perform a $\chi^2$ analysis of neutron elastic scattering data off $^{40}$Ca, $^{90}$Zr and $^{208}$Pb at energies $E \approx 5-40$ MeV, assuming a Perey and Buck or Tian, Pang, and Ma non-local form for the optical potential. We introduce energy and asymmetry dependencies in the imaginary part of the potential and refit the data to obtain a global parameterization. Independently of the starting point in the minimization procedure, an energy dependence in the imaginary depth is required for a good description of the data across the included energy range. We present two parameterizations, both of which represent an improvement over the original potentials for the fitted nuclei as well as for other nuclei not included in our fit. Our results show that, even when including the standard Gaussian non-locality in optical potentials, a significant energy dependence is required to describe elastic-scattering data.