Emergence of a secondary rainbow and the dynamical polarization potential for 16O on 12C at 330 MeV

TL;DR

This study investigates how collective excitations influence the nuclear interaction potential in 16O on 12C scattering at 330 MeV, revealing a local dynamical polarization potential responsible for a secondary rainbow and non-local effects.

Contribution

It provides the first detailed analysis of the dynamical polarization potential caused by collective excitations, showing non-uniform forms and non-locality effects in heavy-ion scattering.

Findings

Identification of a local DPP responsible for the secondary rainbow

Evidence of non-locality in the underlying DPP

DPP forms depend on specific nuclear excitations

Abstract

Background: An anomaly in the elastic scattering of O-16 on C-12 around 300 MeV was resolved by including collective excitations of both nuclei, leading to a secondary rainbow. There is little systematic knowledge of the contribution of collective excitations to the interaction between nuclei, particularly in the overlap region of heavy nuclei. Purpose: To study the dynamic polarization potential (DPP) generated by channel coupling that had been validated for a case where scattering is sensitive to the nuclear potential over a wide radial range; to exhibit evidence of the non-locality due to collective coupling; to validate, or otherwise, the representation of DPPs by uniform renormalization of potentials. Methods: S-matrix to potential inversion yields local potentials reproducing the elastic channel S-matrix of coupled channel calculations. Subtracting the elastic channel uncoupled potential yields a local L-independent representation of the DPP. The dependence of the DPP on the nature of the coupled states and other parameters can be studied. Results: Local DPPs were found due to the excitation of C-12 and the combined excitation of O-16 and C-12. The radial forms found were very different from uniform renormalization of the potential. Full coupling led to a 10 percent increase in the volume integral of the real potential. Evidence for the non-locality of the underlying formal DPP and the effect of direct coupling between the collective states is found. Conclusions: The local DPP generating the secondary rainbow is found. DPPs have forms depending on the specific excitations and cannot be represented by a uniform renormalization of the potential. The method is useful for study of the contribution of collective excitations to internuclear potentials, concerning which remarkably little is known in general.