Dependence of calculated binding energies and widths of $\eta$-mesic nuclei on treatment of subthreshold $\eta$-nucleon interaction

Abstract

We demonstrate that the binding energies and widths of eta-mesic nuclei depend strongly on subthreshold eta-N interaction. This strong dependence is made evident from comparing three different eta-nucleus optical potentials: (1) a microscopic optical potential taking into account the full effects of off-shell eta-nucleon interactions; (2) a factorization approximation to the microscopic optical potential where a downward energy shift parameter is introduced to approximate the subthreshold eta-nucleon interaction; and (3) an optical potential using on-shell eta-nucleon scattering length as the interaction input. Our analysis indicates that the in-medium $\eta$N interaction for bound-state formation is about 30 MeV below the free-space $\eta$N threshold, which causes a substantial reduction of the attractive force between the $\eta$ and nucleon with respect to that implied by the scattering length. Consequently, the scattering-length approach overpredicts the binding energies and caution must be exercised when these latter predictions are used as guide in searching for $\eta$-nucleus bound states. We also show that final-state-interaction analysis cannot provide an unequivocal determination of the existence of $\eta$-nucleus bound state. More direct measurements are, therefore, necessary.

28 pages, 1 figure

References in corpus (1)

• A coupled K-matrix description of the reactions pi+N -> pi+N, pi+N -> eta+N, gamma+N -> pi+N and gamma+N -> eta+N

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