Quantifying uncertainties due to optical potentials in one-neutron knockout reactions

TL;DR

This paper quantifies and propagates uncertainties in optical potentials used in one-neutron knockout reaction models, revealing significant theoretical uncertainties that affect the extraction of nuclear structure information.

Contribution

It introduces a Bayesian framework to quantify and compare uncertainties from phenomenological and microscopic optical potentials in knockout reactions.

Findings

Uncertainty in optical potentials can be as large as experimental errors.

Theoretical uncertainties are about 20% for halo nuclei and 40% for tightly-bound nuclei.

Microscopic and phenomenological approaches yield similar confidence interval widths.

Abstract

One-neutron knockout reactions have been widely used to extract information about the single-particle structure of nuclei from the valley of stability to the driplines. The interpretation of knockout data relies on reaction models, where the uncertainties are typically not accounted for. In this work we quantify uncertainties of optical potentials used in these reaction models and propagate them, for the first time, to knockout observables using a Bayesian analysis. We study two reactions in the present paper, the first of which involves a loosely-bound halo projectile, $^{11}$Be, and the second a tightly-bound projectile, $^{12}$C. We first quantify the parametric uncertainties associated with phenomenological optical potentials. Complementing to this approach, we also quantify the model uncertainties associated with the chiral forces that can be used to construct microscopic optical potentials. For the phenomenological study, we investigate the impact of the imaginary terms of the optical potential on the breakup and stripping components of the knockout cross sections as well as the impact of the angular range. For the $^{11}$Be case, the theoretical uncertainty from the phenomenological method is on the order of the experiment uncertainty on the knockout observables; however, for the $^{12}$C case, the theoretical uncertainty is significantly larger. The widths of the confidence intervals for the knockout observables obtained for the microscopic study and the phenomenological approach are of similar order of magnitude. Based on this work we conclude that structure information inferred from the ratio of the knockout cross sections, will carry a theoretical uncertainty of at least $20\%$ for halo nuclei and at least $40\%$ for tightly-bound nuclei.