Measurement of Γ( φ → η ′ γ ) / Γ( φ → ηγ ) and the pseudoscalar mixing angle The KLOE Collaboration

We have measured the radiative decays φ → ηγ , φ → η ′ γ selecting π + π − γ γ γ final state in a sample of ∼ 5 × 10 7 φ -mesons produced at the Frascati φ –factory DAΦNE. We obtain Γ( φ → η ′ γ ) / Γ( φ → ηγ ) = (4 . 70 ± 0 . 47 ± 0 . 31) × 10 − 3 . From this result we derive new accurate values for the branching ratio BR( φ → η ′ γ ) = (6 . 10 ± 0 . 61 ± 0 . 43) × 10 − 5 and the mixing angle of pseudoscalar mesons in the flavour basis ϕ P = (41 . 8 +1 . 9 − 1 . 6 ) ◦ .