Coulomb and nuclear effects in breakup and reaction cross sections

TL;DR

This paper uses a three-body CDCC model to analyze Coulomb and nuclear effects in breakup and reaction cross sections, highlighting ambiguities in their separation and proposing methods to improve convergence and definitions.

Contribution

It introduces two methods for separating Coulomb and nuclear effects in breakup and reaction cross sections within a three-body CDCC framework, addressing convergence and definitional issues.

Findings

Large ambiguity in defining Coulomb and nuclear breakup cross sections.

Nuclear effects dominate reaction cross sections above the Coulomb barrier.

Proposed a third method to improve convergence at high angular momentum.

Abstract

We use a three-body Continuum Discretized Coupled Channel (CDCC) model to investigate Coulomb and nuclear effects in breakup and reaction cross sections. The breakup of the projectile is simulated by a finite number of square integrable wave functions. First we show that the scattering matrices can be split in a nuclear term, and in a Coulomb term. This decomposition is based on the Lippmann-Schwinger equation, and requires the scattering wave functions. We present two different methods to separate both effects. Then, we apply this separation to breakup and reaction cross sections of 7Li + 208Pb. For breakup, we investigate various aspects, such as the role of the alpha + t continuum, the angular-momentum distribution, and the balance between Coulomb and nuclear effects. We show that there is a large ambiguity in defining the 'Coulomb' and 'nuclear' breakup cross sections, since both techniques, although providing the same total breakup cross sections, strongly differ for the individual components. We suggest a third method which could be efficiently used to address convergence problems at large angular momentum. For reaction cross sections, interference effects are smaller, and the nuclear contribution is dominant above the Coulomb barrier. We also draw attention on different definitions of the reaction cross section which exist in the literature, and which may induce small, but significant, differences in the numerical values.