Measurement of Γ(η→π^+π^-γ)/Γ(η→π^+π^-π^0) with KLOE experiment

We report the measurement of the ratio Γ(η→π^+π^-γ)/Γ(η→π^+π^-π^0) analyzing a large sample of ϕ→ηγ decays recorded with the KLOE experiment at the DAΦNE e^+ e^- collider, corresponding to an integrated luminosity of 558 pb^-1. The η→π^+π^-γ process is supposed to proceed both via a resonant contribution, mediated by the ρ 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_η=Γ(η→π^+ π^- γ)/Γ(η→π^+ π^- π^0)= 0.1838± 0.0005_stat± 0.0030_syst is in agreement with a recent CLEO measurement, which differs by more 3 σ from the average of previous results.