title: Observation of strong low-lying E1 strength in the two-neutron halo nucleus 11Li.
abstract: An exclusive measurement has been made of the Coulomb dissociation of the two-neutron halo nucleus 11Li at 70 MeV/nucleon at RIKEN. Strong low-energy (soft) E1 excitation is observed, peaked at about Ex = 0.6 MeV with B(E1) = 1.42(18) e2fm2 for Erel < or = 3 MeV, which was largely missed in previous measurements. This excitation represents the strongest E1 transition ever observed at such low excitation energies. The spectrum is reproduced well by a three-body model with a strong two-neutron correlation, which is further supported by the E1 non-energy-weighted cluster sum rule.
authors.affiliation: Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan.
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authors.lastname: Nakamura
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authors.lastname: Vinodkumar
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authors.lastname: Sugimoto
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authors.lastname: Hasegawa
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authors.lastname: Kobayashi
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authors.lastname: Saito
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authors.lastname: Sakurai
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authors.lastname: Shimoura
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authors.lastname: Watanabe
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authors.lastname: Watanabe
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authors.lastname: Yakushiji
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authors.lastname: Yanagisawa
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authors.initials: K
authors.lastname: Yoneda