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We report the first observation of the rare η→e+e−e+e−(γ) decay based on 1.7 fb−1 collected by the KLOE experiment at the DAΦNE ϕ-factory. The selection of the e+e−e+e− final state is fully inclusive of radiation. We have identified 362±29 events resulting in a branching ratio of (2.4±0.2stat+bckg±0.1syst)×10−5.
We have studied the η→π+π−e+e−(γ) decay using about 1.7 fb−1 collected by the KLOE experiment at the DAΦNE ϕ-factory. This corresponds to about 72 millions η mesons produced in ϕ radiative decays. We have measured the branching ratio, inclusive of radiative effects, with 4% accuracy: BR(η→π+π−e+e−(γ))=(26.8±0.9Stat.±0.7Syst.)×10−5. We have obtained the first measurement of the CP-odd ππ–ee decay planes...
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