Measurement of η → π0γγ branching fraction with the KLOE detector

A bstract We present a measurement of the doubly radiative decay η → π 0 γγ based on a sample of 82 million η mesons produced in the e + e − → ϕ → ηγ process at the Frascati ϕ -factory DAΦNE. From the data analysis, 1246 ± 133 signal events were observed. By normalising the signal to the well-known η → 3 π 0 decay the branching fraction B (^0) is measured to be (0. 98 ± 0. 11 stat ± 0. 14 syst) × 10 − 4. This result agrees with a preliminary KLOE measurement, but is a factor of two smaller than the current world average. Results for d Γ (η → π 0 γγ) /dM 2 (γγ) are also presented and compared with the latest theoretical predictions.