Measurement of the pseudoscalar mixing angle and $\eta^{\prime}$ gluonium content with KLOE detector

TL;DR

This paper measures the ratio of radiative phi decays to eta and eta' mesons, deriving the pseudoscalar mixing angle and gluonium content of eta', providing insights into meson structure.

Contribution

It presents a precise measurement of the decay ratio R_phi and estimates the gluonium content and mixing angle of eta' meson, advancing understanding of meson mixing and gluonium presence.

Findings

Measured R_phi = (4.77 ± 0.09_stat ± 0.19_sys) x 10^{-3}

Estimated gluonium fractional content Z^2 = 0.14 ± 0.04

Derived pseudoscalar mixing angle φ_P ≈ 39.7°

Abstract

We have measured the ratio $R_{\phi}=BR(\phi \to \eta^{\prime} \gamma)/BR(\phi \to \eta \gamma)$ by looking for the radiative decays $\phi \to \eta^{\prime} \gamma$ and $\phi \to \eta \gamma$ in the final states $\pi^+\pi^-$ 7 $\gamma$'s and 7 $\gamma$'s respectively, in a sample of $\sim 1.3\cdot 10^{9}$ $\phi$ mesons produced at the Frascati $\phi$-factory. We obtain $R_{\phi}=(4.77\pm0.09_{stat}\pm0.19_{sys})\cdot 10^{-3}$ from which we derive $BR(\phi \to \eta^{\prime} \gamma)=(6.20\pm0.11_{stat}\pm0.25_{sys})\cdot 10^{-5}$. In the hypothesis of no gluonium content we extract the pseudoscalar mixing angle in the quark-flavor basis $\phi_P=(41.4\pm0.3_{stat}\pm0.7_{sys}\pm0.6_{th})^{\circ}$. Combining the value of $R_{\phi}$ with other constraints, we estimate the gluonium fractional content of $\eta^{\prime}$ meson as $Z^2 = 0.14\pm0.04$ and the mixing angle $\phi_P = (39.7\pm0.7)^{\circ}$.