η bound states in nuclei: a probe of flavour-singlet dynamics

We argue that η bound states in nuclei are sensitive to the singlet component in the η. The bigger the singlet component, the more attraction and the greater the binding. Thus, measurements of η bound states will yield new information about axial U(1) dynamics and glue in mesons. η-η′ mixing plays an important role in understanding the value of the η-nucleon scattering length.