Measurement of $\Gamma(\eta \to \pi^+\pi^-\gamma)/\Gamma(\eta \to   \pi^+\pi^-\pi^0)$ with KLOE experiment
  We report the measurement of the ratio $\Gamma(\eta \to \pi^+\pi^-\gamma)/\Gamma(\eta \to \pi^+\pi^-\pi^0)$ analyzing a large sample of $\phi \to \eta \gamma$ decays recorded with the KLOE experiment at the DA$\Phi$NE $e^+ e^-$ collider, corresponding to an integrated luminosity of 558 pb$^{-1}$. The $\eta \to \pi^+\pi^-\gamma$ process is supposed to proceed both via a resonant contribution, mediated by the $\rho$ meson, and a non resonant direct term, connected to the box anomaly. The presence of the direct term affects the partial width value. Our result $R_{\eta}=\Gamma(\eta \to \pi^+ \pi^- \gamma)/\Gamma(\eta \to \pi^+ \pi^- \pi^0)= 0.1838\pm 0.0005_{stat} \pm 0.0030_{syst}$ is in agreement with a recent CLEO measurement, which differs by more 3 $\sigma$ from the average of previous results. 
The KLOE Collaboration: F. Ambrosino, A. Antonelli, M. Antonelli, F.   Archilli, I. Balwierz, G. Bencivenni, C. Bini, C. Blo...
hep-ex