Upper limit on the η → π + π − branching fraction with the KLOE experiment
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Babusci D., Berlowski M., Bloise C., Bossi F., Branchini P., Budano A., Cao B., Ceradini F., Ciambrone P., Curciarello F., Czerwinski E., D'Agostini G., Dane E., De Leo V., De Lucia E., De Santis A., De Simone P., Di Cicco A., Di Domenico A., Domenici D., D'Uffizi A., Fantini A., Fermani P., Fiore S., Gajos A., Gauzzi P., Giovannella S., Graziani E., Ivanov V. L., Johansson T., Kang X., Kisielewska-Kaminska D., Kozyrev E. A., Krzemien W., Kupsc A., Lukin P. A., Mandaglio G., Martini M., Messi R., Miscetti S., Moricciani D., Moskal P., Parzych S., Passeri A., Patera V., Perez del Rio E., Santangelo P., Schioppa M., Selce A., Silarski M., Sirghi F., Solodov E. P., Tortora L., Venanzoni G., Wislicki W., Wolke M.
ISSN: 1029-8479
Based on an integrated luminosity of 1.61 fb−1e+e− collision data collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory, a search for the P- and CP-violating decay η → π+π− has been performed. Radiative ϕ → ηγ decay is exploited to access the η mesons. No signal is observed in the π+π− invariant mass spectrum, and the upper limit on the branching fraction at 90% confidence level is determined to be ℬ(η → π+π−) < 4.9 × 10−6, which is approximately three times smaller than the previous KLOE result. From the combination of these two measurements we get ℬ(η → π+π−) < 4.4 × 10−6 at 90% confidence level.