Search for bound η-nucleus states

Abstract

The extracted s-wave scattering amplitude from both the polarized and unpolarized d + d → ⁴He + η reaction at 2385.5 MeV/c allowed to determine the scattering length which fulfills the requirements for bound η. In the p + ²⁷Al → ³He + p + Π^- + X reaction studied at recoil free kinematics the η meson is produced almost at rest and so it can be bound with enhanced probability. This state proceeds via N^∗(1535) resonance and the decay products proton and pion emitted into opposite direction are detected in concidence with ³He produced at zero degree. Under these conditions some hints for bound state can be observed with an upper limit of the cross section of ≈0.5 nb.