Spectroscopy of He$^{7}$ using the Be$^{9}$(He$^{6}$,Be$^{8}$) transfer reaction

The unbound nucleus He7 has been investigated via the reaction of a 16.8 MeV He6 radioactive ion beam on a Be9 target. The measurement of the outgoing Be8 through its well characterized two-α decay permitted the energy of the He6+n system to be reconstructed. Through comparison with a complete Monte Carlo simulation incorporating R-matrix lineshapes, the He7 ground state was determined to lie 0.380(28) MeV above the neutron decay with a width of Γ=0.179(21) MeV. A neutron spectroscopic factor SF=0.608(18) was extracted in agreement with the most recent calculations. Significant evidence was found for a broad resonance lying at 2.6(2) MeV above threshold with a ΓFWHM=2.3(3) MeV. These parameters are fully consistent with the properties of 1/2− state reported by Wuosmaa et al. [Phys. Rev. C 72, 061301(R) (2005)]. Limits were also put on the presence of narrow resonances seen in earlier experiments.