η^′ gluonic content and J / ψ → V P 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 φ{symbol}P = (40.5 ± 2.4) °. In presence of gluonium, the values for the mixing angle and the gluonic content of the η′ wave function are φ{symbol}P = (44.5 ± 4.3) ° and Zη′2 = 0.28 ± 0.21, respectively. Corrections due to non-ideal ω-φ{symbol} mixing are shown to be negligible. The newly reported values of B (J / ψ → ρ π) by the BABAR and BES Collaborations are crucial to get a consistent description of data. © 2008 Elsevier B.V. All rights reserved.