η — η′ glueball mixing from photon-meson transition form factors and the decay ratio Ds → ηlv/η′lv

We have determined (a) the η/η′ mixing angle and (b) the regions of the allowed admixture of the glueball component with JPC = 0−+ in η and η′, based on transition form factors η → γγ* and η′ → γγ* at 0 ≤ Q2 ≤ 20 GeV2/C2, and the branching ratio Ds → ηlv/η′lv. For η and η′ wave functions, η = cos α (cos θ nn̄ — sin θ ss̄) + sin α G and η′ = cos ga′ (sin θ′ nn̄ + cos θ′ ss̄ + sin α− G where nn̄) = (uū + dd̄) / √2 and G means a glueball, a shape of the allowed region in the (θ, α, α′) space is determined which is located inside the borders 0.56 ≤ sin θ ≤ 0.67, sin2 α ≤ 0.08, sin2 α′ ≤ 0.20. This corresponds to θp = −16.7° ± 2.8° (90% confidence level).