COUPLED-CHANNEL CALCULATION OF BOUND AND RESONANT SPECTRA OF $^9_\Lambda{\rm Be}$ AND $^{13}_\Lambda\rm C$ HYPERNUCLEI

Abstract

A multi-channel algebraic scattering (MCAS) approach has been used to analyze the spectra of two hypernuclear systems, [Formula: see text] and [Formula: see text]. The splitting of the two odd-parity excited levels ([Formula: see text] and [Formula: see text]) at 11 MeV excitation in [Formula: see text] is driven mainly by the weak Λ-nucleus spin–orbit force, but the splittings of the [Formula: see text] and [Formula: see text] levels in both [Formula: see text] and [Formula: see text] 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 [Formula: see text] 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 [Formula: see text] is inverted with respect to that currently observed. In both hypernuclei, our calculations suggest that there are additional low-lying resonant states in the Λ-nucleus continua.