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

TL;DR

This paper refines the eta-eta' mixing angle and gluonium content using updated decay data, finding consistent mixing angles and small gluonium admixture in eta' with some variation depending on the decay process.

Contribution

It provides a new phenomenological analysis of eta-eta' mixing and gluonium content based on recent decay measurements, improving previous estimates.

Findings

Mixing angle around 41.5 degrees without gluonium

Gluonium content of eta' is small, Z^2_eta' ≈ 0.04

Different decay channels yield consistent mixing angles

Abstract

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