Upper limit on the η → π + π − branching fraction with the KLOE experiment

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.

doi:10.1007/JHEP10(2020)047

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.

Upper limit on the η → π + π − branching fraction with the KLOE experiment / 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., et al.. - In: JOURNAL OF HIGH ENERGY PHYSICS. - ISSN 1029-8479. - 2020:10(2020). [10.1007/JHEP10(2020)047]