Se p 19 99 Correlator of Topological Charge Densities in Instanton Model in QCD .

The QCD sum rule for the correlator of topological charge densities χ(Q2) and related to it longitudinal part of the correlator of singlet axial currents is considered in the framework of instanton model. The coupling constant fη′ of η -meson with the singlet axial current is determined. Its value appears to be in a good coincidence with the value determined recently from the connection of the part of proton spin Σ, carried by u, d, s quarks, with the derivative of QCD topological susceptibility χ(0). From the same sum rule η − η mixing angle θ8 is found in the framework of two mixing angles model. The value of θ8 is close to that found in the chiral effective theory. The correlator of topological charge densities χ(Q2) at large Q2 is calculated and it was found that its Q2-dependence matches well with Q2-dependence at low Q2 determined by the known χ(0) and by contributions of πand η-mesons. e-mail:[email protected] e-mail:[email protected]