Coupled-channel calculation of bound and resonant spectra of Lambda-9Be and Lambda-13C hypernuclei

TL;DR

This paper employs a Multi-Channel Algebraic Scattering approach to analyze the spectra of Lambda-9Be and Lambda-13C hypernuclei, revealing the roles of spin-orbit and coupling effects in their level structures.

Contribution

It introduces a phenomenological potential-based MCAS method to accurately reproduce hypernuclear spectra and elucidates the mechanisms behind level splittings and orderings.

Findings

Reproduces observed level splittings in Lambda-9Be and Lambda-13C.

Identifies the dominant role of spin-orbit and coupling effects in level structures.

Suggests existence of additional low-lying resonant states in hypernuclei.

Abstract

A Multi-Channel Algebraic Scattering (MCAS) approach has been used to analyze the spectra of two hyper-nuclear systems, Lambda-9Be and Lambda-13C. The splitting of the two odd-parity excited levels (1/2^- and 3/2^-) at 11 MeV excitation in Lambda-13C is driven mainly by the weak Lambda-nucleus spin-orbit force, but the splittings of the 3/2^+ and 5/2^+ levels in both Lambda-9Be and Lambda-13C have a different origin. These cases appear to be dominated by coupling to the collective 2+ states of the core nuclei. Using simple phenomenological potentials as input to the MCAS method, the observed splitting and level ordering in Lambda-9Be is reproduced with the addition of a weak spin-spin interaction acting between the hyperon and the spin of the excited target. With no such spin-spin interaction, the level ordering in Lambda-9Be is inverted with respect to that currently observed. In both hyper-nuclei, our calculations suggest that there are additional low-lying resonant states in the Lambda-nucleus continua.