Charge radii and neutron correlations in helium halo nuclei
  Within the complex-energy configuration interaction framework, we study correlations of valence neutrons to explain the behavior of charge radii in the neutron halo nuclei $^{6,8}$He. We find that the experimentally observed decrease of the charge radius between $^6$He and $^8$He is caused by a subtle interplay between three effects: dineutron correlations, a spin-orbit contribution to the charge radius, and a core swelling effect. We demonstrate that two-neutron angular correlations in the $2^+_1$ resonance of $^6$He differ markedly from the ground-state correlations in $^{6,8}$He. 
G. Papadimitriou, A.T. Kruppa, N. Michel, W. Nazarewicz, M.   P{\l}oszajczak, J. Rotureau
nucl-th nucl-ex