First Results of a ⁸He+d Experiment

Secondary ⁸He beam delivered by the fragment separator ACCULINNA was used in an experiment designed for the simultaneous study of the ⁷H and ⁹He exotic nuclei. Attempt to observe ⁷H produced in the reaction ²H(⁸He,³He)⁷H resulted only in setting a cross section limit, dσ/dΩ < 20 μb/sr, for the reaction channel which could populate a resonance lying between 0 and 3 MeV above the ⁷H decay threshold. The spectrum of ⁹He was studied by means of the ²H(⁸He,p)⁹He reaction. Energy and angular correlations were obtained for the ⁹He decay products by complete kinematical reconstruction. The lowest resonant state of ⁹He is found at about 2 MeV with a width of ∼2 MeV and is identified as 1/2⁻. The observed angular correlation pattern is uniquely explained by the interference of the 1/2⁻ resonance with a virtual state 1/2⁺ (a limit of a₀ > −20 fm on the scattering length is obtained), and with a 5/2⁺ resonance located at ∼4.2 MeV.