Two-neutron correlations inHe6in a Coulomb breakup reaction

Abstract

We investigate the three-body Coulomb breakup of a two-neutron halo nucleus, $^{6}\mathrm{He}$. Based on the $\ensuremath{\alpha}+n+n$ model, the three-body scattering states of $^{6}\mathrm{He}$ are described by using the combined methods of the complex scaling and the Lippmann-Schwinger equation. We calculate the breakup cross section, the two-dimensional energy distributions, and the invariant mass spectra for the $E1$ transition of $^{6}\mathrm{He}$. We discuss the relations between the structures in these strengths and the $n$-$n$ and $\ensuremath{\alpha}$-$n$ correlations of $^{6}\mathrm{He}$. It is found that the $^{5}\mathrm{He}$ resonance in the final states contributes to make a low-energy enhancement of the strength. The $n$-$n$ final-state interaction also contributes to enhance the strength globally. However, the ground-state correlations of $^{6}\mathrm{He}$, such as a dineutron, are difficult to recognize in the strength because of the dominant effect of the final-state interaction.