S-MATRIX AND R-MATRIX DETERMINATION OF THE LOW-ENERGY HE-5 AND LI-5 RESONANCE PARAMETERS

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