Neutron versus proton scattering on exotic nuclei: the $^9$He example

Abstract

Neutron scattering on exotic nuclides is a class of processes which can not be studied directly now and in any observable future. Resonance proton scattering of exotic nuclide on a thick target in inverse kinematics can be used to infer the properties of the low-energy neutron scattering of this nuclide assuming the isobaric symmetry. However, the results of such resonance proton scattering reactions are so far analyzed in theoretical approaches (optical, R-matrix models), which are missing important aspects of isospin dynamics, isospin violation in continuum and threshold dynamics. The isospin conserving coupled-channel model (ICM) is proposed, which provides a more reliable basis for understanding of such experimental studies. Qualitatively different phase shifts for the $^{8}$He+$p$ $T=5/2$ and $T=3/2$ resonances are predicted by ICM with quite unusual profile for the $T=5/2$ states. Alternative interpretation of the existing $^{8}$He+$p$ data is proposed. The observable properties of the $T=5/2$ resonances may be strongly affected by the isobaric-partner $T=3/2$ states. Crucial importance of studies of the neutron-emission channel for disentangling this possible influence is demonstrated.