The η-η′ mixing angle and the relative radiative decay rates Γ(ψ→ηγ)Γ(ψ→η′γ)

The problem of η-η′ mixing is reexamined within the nonet scheme. It is shown that the mixing angle θ_p is quite sensitive to a small SU(3) violating $\text{27}$ piece. Taking SU(3) violating q$\text{q}$ annihilation terms into account, we obtain a large ratio $\text{Γ(ψ→ηγ)}\text{Γ(ψ→η′γ)}$ which is largely independent of the mixing angle and agrees with the measured value to within 20–30%.