On Eta-Meson Interaction with Nuclear Matter

The transparency of the carbon nucleus with respect to eta mesons of energy 25 to 95 MeV was measured. Mesons of this energy originated from the photoproduction on quasifree protons of the carbon nucleus ( γ p→η p ) under the effect of photons with energies between 720 and 770 MeV. The inelastic cross sections for η N interaction in nuclear matter are determined from the measured transparency of the nucleus. The absence of nucleon resonances in the measured cross section—in particular, the S_11 resonance, which is usually associated with the assumption of the existence of eta-meson nuclei—is discussed.