Soft electric dipole (E1) response of11Li has been investigated by a kinematical complete measurement of the Coulomb breakup at about 70 MeV/nucleon. A two-wall neutron detector setup allowed us to employ a kinematical condition to exclude fully the cross talk events even for the low relative energies (Erel) down to 0 MeV, thereby enhancing the experimental sensitivities in this energy region. In the Erelspectrum, a strong peak corresponding to the soft E1 excitation has been observed at about Ex= 0.6 MeV with B (E1) = 1.42 (18) e2 fm2(4.5(6) Weisskopf units) for 0 ≤ Erel≤ 3 MeV. The spectral shape as well as its amplitude is in excellent agreement with a three-body model with strong neutron-neutron correlation in the halo. Such correlation is further supported by the E1 non-energy weighted cluster sum rule. © 2007 Elsevier B.V. All rights reserved.
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