A global fit to determine the pseudoscalar mixing angle and the gluonium content of the eta ' meson

We update the values of the eta-eta' mixing angle and of the eta' gluonium content by fitting our measurement R(phi) = BR(phi -> eta gamma)/BR(phi -> eta gamma) together with several vector meson radiative decays to pseudoscalars (V -> P gamma), pseudoscalar mesons radiative decays to vectors (P -> V gamma) and the eta' -> gamma gamma, pi(0) -> gamma gamma widths. From the fit we extract a gluonium fraction of Z(G)(2) = 0.12 +/- 0.04, the pseudoscalar mixing angle psi(P) = (40.4 +/- 0.6)degrees and the phi - omega mixing angle psi(V) = (3.32 +/- 0.09)degrees. Z(G)(2) and psi(P) are fairly consistent with those previously published. We also evaluate the impact on the eta' gluonium content determination of future experimental improvements of the eta' branching ratios and decay width.