Measurement of the branching ratio and search for a CP violating asymmetry in the η→π+π−e+e−(γ) decay at KLOE

• Published in: Physics letters. B 2009-05, Vol.675 (3-4), p.283-288
• Main Authors: Ambrosino, F., Antonelli, A., Antonelli, M., Archilli, F., Beltrame, P., Bencivenni, G., Bertolucci, S., Bini, C., Bloise, C., Bocchetta, S., Bossi, F., Branchini, P., Capon, G., Capussela, T., Ceradini, F., Ciambrone, P., Crucianelli, F., De Lucia, E., De Santis, A., De Simone, P., De Zorzi, G., Denig, A., Di Domenico, A., Di Donato, C., Di Micco, B., Dreucci, M., Felici, G., Fiore, S., Franzini, P., Gatti, C., Gauzzi, P., Giovannella, S., Graziani, E., Lanfranchi, G., Lee-Franzini, J., Leone, D., Martini, M., Massarotti, P., Meola, S., Miscetti, S., Moulson, M., Müller, S., Murtas, F., Napolitano, M., Nguyen, F., Palutan, M., Pasqualucci, E., Passeri, A., Patera, V., Perfetto, F., Santangelo, P., Sciascia, B., Spadaro, T., Testa, M., Tortora, L., Valente, P., Venanzoni, G., Versaci, R., Xu, G.
• Format: Article
• Language: English
• Subjects: [formula omitted] collisions; CP violation; Exact sciences and technology; Nuclear physics; Physics; Rare η decays; The physics of elementary particles and fields
• ISSN: 0370-2693; 1873-2445
• DOI: 10.1016/j.physletb.2009.04.013

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 angular asymmetry, Aϕ=(−0.6±2.5Stat.±1.8Syst.)×10−2.