η′ gluonic content and J/ψ→VP decays

The η-η′ pseudoscalar mixing angle and the gluonium content of the η′ meson are deduced from an updated phenomenological analysis of J/ψ decays into a vector and a pseudoscalar meson. In absence of gluonium, the value of the mixing angle in the quark-flavour basis is found to be ϕP=(40.5±2.4)°. In presence of gluonium, the values for the mixing angle and the gluonic content of the η′ wave function are ϕP=(44.5±4.3)° and , respectively. Corrections due to non-ideal ω-ϕ mixing are shown to be negligible. The newly reported values of B(J/ψ→ρπ) by the BABAR and BES Collaborations are crucial to get a consistent description of data.