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

We update the values of the η-η' mixing angle and of the η' gluonium content by fitting our measurement R = BR( → η'γ)/BR( → ηγ) together with several vector meson radiative decays to pseudoscalars (V → Pγ), pseudoscalar mesons radiative decays to vectors (P → Vγ) and the η' → γγ, π0 → γγ widths. From the fit we extract a gluonium fraction of ZG2 = 0.12±0.04, the pseudoscalar mixing angle ψP = (40.4±0.6)° and the −ω mixing angle ψV = (3.32±0.09)°. ZG2 and ψP are fairly consistent with those previously published. We also evaluate the impact on the η' gluonium content determination of future experimental improvements of the η' branching ratios and decay width.