S-matrix and R-matrix determination of the low-energy He-5 and Li-5 resonance parameters

Abstract

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 reproduced well. 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, which 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 which works at complex energies.

9 pages, 1 figure. Final version. Slightly rewritten, results and conclusions unchanged