First observation and study of the K± → π±π0e+e− decay

Batley, J. R.; Kalmus, G.; Lazzeroni, C.; Munday, D. J.; Slater, M. W.; Wotton, S. A.; Arcidiacono, R.; Bocquet, G.; Cabibbo, N.; Ceccucci, A.; Cundy, D.; Falaleev, V.; Fidecaro, M.; Gatignon, L.; Gonidec, A.; Kubischta, W.; Maier, A.; Norton, A.; Patel, M.; Peters, A.; Balev, S.; Frabetti, P. L.; Gersabeck, E.; Goudzovski, E.; Hristov, P.; Kekelidze, V.; Kozhuharov, V.; Litov, L.; Madigozhin, D.; Misheva, M.; Molokanova, N.; Polenkevich, I.; Potrebenikov, Yu.; Stoynev, S.; Zinchenko, A.; Monnier, E.; Swallow, E.; Winston, R.; Rubin, P.; Walker, A.; Dalpiaz, P.; Damiani, C.; Fiorini, M.; Martini, M.; Petrucci, F.; Savrié, M.; Scarpa, M.; Wahl, H.; Baldini, W.; Cotta Ramusino, A.; Gianoli, A.; Calvetti, M.; Celeghini, E.; Iacopini, E.; Lenti, M.; Ruggiero, G.; Bizzeti, A.; Veltri, M.; Behler, M.; Eppard, K.; Hita-Hochgesand, M.; Kleinknecht, K.; Marouelli, P.; Masetti, L.; Moosbrugger, U.; Morales Morales, C.; Renk, B.; Wache, M.; Wanke, R.; Winhart, A.; Coward, D.; Dabrowski, A.; Fonseca Martin, T.; Shieh, M.; Szleper, M.; Velasco, M.; Wood, M. D.; Anzivino, G.; Imbergamo, E.; Nappi, A.; Piccini, M.; Raggi, M.; Valdata-Nappi, M.; Cenci, P.; Pepe, M.; Petrucci, M. C.; Costantini, F.; Doble, N.; Fiorini, L.; Giudici, S.; Pierazzini, G.; Sozzi, M.; Venditti, S.; Collazuol, G.; Dilella, L.; Lamanna, G.; Mannelli, I.; Michetti, A.; Cerri, C.; Fantechi, R.; Bloch-Devaux, B.; Cheshkov, C.; Chèze, J. B.; De Beer, M.; Derré, J.; Marel, G.; Mazzucato, E.; Peyaud, B.; Vallage, B.; Holder, M.; Ziolkowski, M.; Bifani, S.; Clemencic, M.; Goy Lopez, S.; Biino, C.; Cartiglia, N.; Marchetto, F.; Dibon, H.; Jeitler, M.; Markytan, M.; Mikulec, I.; Neuhofer, G.; Widhalm, L.

doi:10.1016/j.physletb.2018.11.046

The NA48/2 experiment at CERN reports the first observation of the K±→π±π0e+e− decay from an exposure of 1.7×1011 charged kaon decays recorded in 2003–2004. A sample of 4919 candidates with 4.9% background contamination allows the determination of the branching ratio in the full kinematic region, BR(K±→π±π0e+e−)=(4.24±0.14)×10−6. The study of the kinematic space shows evidence for a structure dependent contribution in agreement with predictions based on chiral perturbation theory. Several P- and CP-violating asymmetries are also evaluated.

First observation and study of the K± → π±π0e+e− decay / Batley, J.R., Kalmus, G., Lazzeroni, C., Munday, D.J., Slater, M.W., Wotton, S.A., Arcidiacono, R., Bocquet, G., Cabibbo, N., Ceccucci, A., Cundy, D., Falaleev, V., Fidecaro, M., Gatignon, L., Gonidec, A., Kubischta, W., Maier, A., Norton, A., Patel, M., Peters, A., et al.. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - 788:(2019), pp. 552-561. [10.1016/j.physletb.2018.11.046]