Coulomb dissociation reaction and correlations of two halo neutrons in 11Li

We have performed an exclusive measurement for the Coulomb dissociation reaction, Pb(11Li,9Li+2n)X at an incident energy of 43 A MeV. The deduced excitation energy spectrum of the 11Li nucleus shows a prominent peak at 1 MeV with a large tail towards higher excitation energies. The relative energy spectra for the n-n and 9Li−2n sub-systems show that the excitation is dominated by the relative motion between 9Li and the center-of-mass of the two neutrons. The above characteristics are explained by a direct Coulomb breakup mechanism with an extended ‘di-neutron’ model.