Breakup correlations and continuum spectroscopy of two-neutron halo nuclei

Continuum spectroscopy implies a consistent analysis of a variety of exclusive and inclusive cross sections accessible in kinematically complete experiments. Theoretical analysis of experimental data on different energy correlations of the three fragments from breakup of 6He on lead and carbon targets at collision energy 30 MeV/nucleon, obtained at GANIL, is presented. The applied theory is based on a microscopic four-body distorted wave approach to breakup reactions and uses the three-body model for the nuclear structure of the two-neutron Borromean halo projectile nucleus 6He. The method of hyperspherical harmonics was used for consistent calculations of the ground state wave function and low-lying three-body continuum states including monopole, dipole and quadrupole excitations. Theoretical calculations reproduce quite well the low-lying excitation spectrum and fragment momentum correlations near breakup threshold. Dipole excitation dominates in the spectrum from fragmentation on the lead target, while for fragmentation on carbon excitation of the known 2+ three-body resonance is also important. The theory has previously been successfully tested on 240 MeV/nucleon energy data from GSI. The theory is also applicable to other Borromean nuclei: 11Li, etc.