η -nuclear bound states revisited

The strong energy dependence of the s-wave ηN scattering amplitude at and below threshold, as evident in coupled-channels K-matrix fits and chiral models that incorporate the S11 N⁎(1535) resonance, is included self-consistently in η-nuclear bound-state calculations. This approach, applied recently in calculations of kaonic atoms and K¯-nuclear bound states, is found to impose stronger constraints than ever on the onset of η-nuclear binding, with a minimum value of ReaηN≈0.9 fm required to accommodate an η–He4 bound state. Binding energies and widths of η-nuclear states are calculated within several underlying ηN models for nuclei across the periodic table, including Mgη25 for which some evidence was proposed in a recent COSY experiment.