Eta-eta' mixing from V->Pgamma and J/psi->VP decays

The $\eta$-${\eta }^{\mathrm{\prime }}$ pseudoscalar mixing angle and the gluonium content of the ${\eta }^{\mathrm{\prime }}$ meson are deduced from an updated phenomenological analysis of $V\to P\gamma$ and $J\mathrm{/}\psi \to VP$ decays. In absence of gluonium, the value of the mixing angle in the quark-flavour basis is found to be ${\varphi }_P=(41.5\pm 1.2{)}^{\circ }$ from $V\to P\gamma$ and $\phi_P=(40.5\pm 2.4)^\circ$from$J/\psi\to VP$. In presence of gluonium, the values for the mixing angle and the gluonic content of the ${\eta }^{\mathrm{\prime }}$ wave function are ${\varphi }_P=(41.4\pm 1.3{)}^{\circ }$ and $Z_{{\eta }^{\mathrm{\prime }}}^2=0.04\pm 0.09$ from $V\to P\gamma$and$\phi_P=(44.5\pm 4.3)^\circ$and$Z^2_{\eta^\prime}=0.28\pm 0.21$from$J/\psi\to VP$, respectively.