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Experimental evidence for subshell closure in $^{8}$He and indication of a resonant state in $^{7}$He below 1 MeV

Abstract : The spectroscopy of the unstable $^{8}$He and unbound $^{7}$He nuclei is investigated via the p($^{8}$He, d) transfer reaction with a 15.7A MeV $^{8}$He beam from the SPIRAL facility. The emitted deuterons were detected by the telescope array MUST. The results are analyzed within the coupled-channels Born approximation framework, and a spectroscopic factor $C^2$S=4.4±1.3 for neutron pickup to the $^{7}$He_g.s.$ is deduced. This value is consistent with a full p3/2 subshell for $^{8}$He. Tentative evidence for the first excited state of $^{7}$He is found at $E^*$=0.9±0.5 MeV (width $\Gamma$=1.0±0.9 MeV). The second one is observed at a position compatible with previous measurements, $E^*$=2.9±0.1 MeV. Both are in agreement with previous separate measurements. The reproduction of the first excited state below 1 MeV would be a challenge for the most sophisticated nuclear theories.
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Submitted on : Thursday, December 21, 2006 - 11:21:05 AM
Last modification on : Wednesday, September 16, 2020 - 4:08:30 PM
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F. Skaza, V. Lapoux, N. Keeley, N. Alamanos, E. C. Pollacco, et al.. Experimental evidence for subshell closure in $^{8}$He and indication of a resonant state in $^{7}$He below 1 MeV. Physical Review C, American Physical Society, 2006, 73, pp.044301. ⟨10.1103/PhysRevC.73.044301⟩. ⟨in2p3-00025918⟩

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