We study the low-energy ${3/2}^{-}$ and ${1/2}^{-}$ states of ${}^5$He and ${}^5$Li in a microscopic cluster model. The scattering phase shifts of Bond $(\alpha +n)$ and of Schwandt $(\alpha +p)$, respectively, are well reproduced. We determine the resonance parameters by localizing the poles of the analytically continued $S$ matrix at complex energies. Our results differ from conventional $R$-matrix resonance parameters, that were extracted from experimental data using the definition of a resonance based on the positions and widths of reaction cross section peaks. However, they nicely agree with the results of an extended $R$-matrix method that works at complex energies.

• Received 6 August 1996

DOI:https://doi.org/10.1103/PhysRevC.55.536