Above threshold s-wave resonances illustrated by the [formula omitted] states in 9Be and 9B

Abstract

We solve the persistent problem of the structure of the lowest 1/2+ resonance in 9Be which is important to bridge the A=8 gap in nucleosynthesis in stars. We show that the state is a genuine three-body resonance even though it decays entirely into neutron–8Be relative s-waves. The necessary barrier is created by “dynamical” evolution of the wave function as the short-distance α-5He structure is changed into the large-distance n-8Be structure. This decay mechanism leads to a width about two times smaller than table values. The previous interpretations as a virtual state or a two-body resonance are incorrect. The isobaric analog 1/2+ state in 9B is found to have energy and width in the vicinity of 2.0 MeV and 1.5 MeV, respectively. We also predict another 1/2+ resonance in 9B with similar energy and width.