Measurement of the pseudoscalar mixing angle and eta-prime gluonium content with KLOE detector

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