Unresolved Question of the He-10 Ground State Resonance

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The ground state of He-10 was populated using a 2p2n-removal reaction from a 59 MeV/u Be-14 beam. The decay energy of the three-body system, He-8 + n + n, was measured and a resonance was observed at E = 1.60(25) MeV with a 1.8(4) MeV width. This result is in agreement with previous invariant mass spectroscopy measurements, using the Li-11(-p) reaction, but is inconsistent with recent transfer reaction results. The proposed explanation that the difference, about 500 keV, is due to the effect of the extended halo nature of Li-11 in the one-proton knockout reaction is no longer valid as the present work demonstrates that the discrepancy between the transfer reaction results persists despite using a very different reaction mechanism, Be-14(-2p2n). DOI: 10.1103/PhysRevLett.109.232501