Density distributions of 11Li deduced from reaction cross-section measurements

We measured the reaction cross sections of the two-neutron halo nucleus Li-11 with solid hydrogen and carbon targets at around 31 and 41 MeV/nucleon. The neutron density distribution of Li-11 was deduced for the first time by the Glauber model calculation based on the optical limit approximation. The uncertainty of the matter density of Li-11 was improved, compared with earlier measurements. The present root-mean-square radius of the proton distribution agrees with the previous one derived from an optical isotope shift measurement. The present root-mean-square radii reproduce theoretical calculations by the tensor optimized shell model by assuming core excitation. This consistency suggests the possibility that Li-9 in Li-11 is excited and the disappearance of the N = 8 shell gap of Li-11 is caused by correlations originating from the nucleon force, such as the tensor and the pairing.