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

Understand

We update the values of the eta-eta' mixing angle and of the eta' gluonium content by fitting our measurement R_phi = BR(phi to eta' gamma)/ BR(phi to eta gamma) together with several vector meson radiative decays to pseudoscalars (V to P gamma), pseudoscalar mesons radiative decays to vectors (P to V gamma) and the eta' to gamma gamma, pi^0 to gamma gamma widths.

• From the fit we extract a gluonium fraction of Z^2_G = 0.12 +- 0.04, the pseudoscalar mixing angle psi_P = (40.4 +- 0.6) degree and the phi-omega mixing angle psi_V = (3.32 +- 0.09) degree.
• Z^2_G 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.