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

TL;DR

This paper refines the measurements of the eta' meson's gluonium content and mixing angle using a comprehensive fit to various decay processes, providing updated values and assessing future experimental impacts.

Contribution

It presents a new global fit to determine the eta' meson's gluonium fraction and mixing angle, updating previous estimates with additional decay data and analysis.

Findings

Gluonium fraction Z^2_G = 0.12 ± 0.04

Pseudoscalar mixing angle ψ_P = (40.4 ± 0.6) degrees

Phi-omega mixing angle ψ_V = (3.32 ± 0.09) degrees

Abstract

We update the values of the eta-eta' mixing angle and of the eta' gluonium content by fitting our measurement R_phi = BR(phi to eta' gamma)/ BR(phi to eta gamma) together with several vector meson radiative decays to pseudoscalars (V to P gamma), pseudoscalar mesons radiative decays to vectors (P to V gamma) and the eta' to gamma gamma, pi^0 to gamma gamma widths. From the fit we extract a gluonium fraction of Z^2_G = 0.12 +- 0.04, the pseudoscalar mixing angle psi_P = (40.4 +- 0.6) degree and the phi-omega mixing angle psi_V = (3.32 +- 0.09) degree. Z^2_G and psi_P are fairly consistent with those previously published. We also evaluate the impact on the eta' gluonium content determination of future experimental improvements of the eta' branching ratios and decay width.