Dineutron-dineutron correlation in 8He
Abstract
Background: The four-neutron correlation has been attracting much attention for decades. In addition to the study on the tetra-neutron system, it is worthwhile to investigate the correlation in bound systems. Purpose: The 8He nucleus is a system where four neutrons are weakly bound around the 4He core. The dineutron (2n) correlation has been long discussed in various weakly-bound neutron-rich nuclei such as 6He and 11Li, whereas the 8He nucleus gives us an opportunity to investigate the 2n-2n type four-neutron correlation. Methods: We introduce a microscopic 4 He+4n model and describe the ground-state structure of 8He. The mixing of the two-2n component in the ground state is examined. The ground-state wave function is verified by investigating various observables including high-energy scattering cross sections. Results: Our model reasonably reproduces the available experimental data, the binding energy, charge radius, total reaction cross section, and proton-nucleus elastic scattering cross section data. We find that the significant mixing of the two-2n cluster configurations around 4He in the ground state of 8He: The ground state has a squared overlap of about 45% with a 2n-4He-2n configuration with the 4He-2n distance of 3 fm and opening angle of 80. Conclusion: The ground state of 8He contains a certain amount of the two-2n cluster component, indicating the strong nuclear deformation, which was experimentally observed recently.
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