An investigation of the very rare K+→ π+νν¯ decay

Cortina Gil, E.; Kleimenova, A.; Minucci, E.; Padolski, S.; Petrov, P.; Shaikhiev, A.; Volpe, R.; Numao, T.; Velghe, B.; Bryman, D.; Fu, J.; Husek, T.; Jerhot, J.; Kampf, K.; Zamkovsky, M.; Aliberti, R.; Khoriauli, G.; Kunze, J.; Lomidze, D.; Marchevski, R.; Peruzzo, L.; Vormstein, M.; Wanke, R.; Dalpiaz, P.; Fiorini, M.; Neri, I.; Norton, A.; Petrucci, F.; Wahl, H.; Cotta Ramusino, A.; Gianoli, A.; Iacopini, E.; Latino, G.; Lenti, M.; Parenti, A.; Bizzeti, A.; Bucci, F.; Antonelli, A.; Georgiev, G.; Kozhuharov, V.; Lanfranchi, G.; Martellotti, S.; Moulson, M.; Spadaro, T.; Ambrosino, F.; Capussela, T.; Corvino, M.; Di Filippo, D.; Massarotti, P.; Mirra, M.; Napolitano, M.; Saracino, G.; Anzivino, G.; Brizioli, F.; Imbergamo, E.; Lollini, R.; Piandani, R.; Santoni, C.; Barbanera, M.; Cenci, P.; Checcucci, B.; Lubrano, P.; Lupi, M.; Pepe, M.; Piccini, M.; Costantini, F.; Di Lella, L.; Doble, N.; Giorgi, M.; Giudici, S.; Lamanna, G.; Lari, E.; Pedreschi, E.; Sozzi, M.; Cerri, C.; Fantechi, R.; Pontisso, L.; Spinella, F.; Mannelli, I.; D'Agostini, G.; Raggi, M.; Biagioni, A.; Leonardi, E.; Lonardo, A.; Valente, P.; Vicini, P.; Ammendola, R.; Bonaiuto, V.; Fucci, A.; Salamon, A.; Sargeni, F.; Arcidiacono, R.; Bloch-Devaux, B.; Boretto, M.; Menichetti, E.; Migliore, E.; Soldi, D.; Biino, C.; Filippi, A.; Marchetto, F.; Engelfried, J.; Estrada-Tristan, N.; Bragadireanu, A. M.; Ghinescu, S. A.; Hutanu, O. E.; Baeva, A.; Baigarashev, D.; Emelyanov, D.; Enik, T.; Falaleev, V.; Kekelidze, V.; Korotkova, A.; Litov, L.; Madigozhin, D.; Misheva, M.; Molokanova, N.; Movchan, S.; Polenkevich, I.; Potrebenikov, Y.; Shkarovskiy, S.; Zinchenko, A.; Fedotov, S.; Gushchin, E.; Khotyantsev, A.; Kudenko, Y.; Kurochka, V.; Medvedeva, M.; Mefodev, A.; Kholodenko, S.; Kurshetsov, V.; Obraztsov, V.; Ostankov, A.; Semenov, V.; Sugonyaev, V.; Yushchenko, O.; Bician, L.; Blazek, T.; Cerny, V.; Kucerova, Z.; Bernhard, J.; Ceccucci, A.; Danielsson, H.; De Simone, N.; Duval, F.; Dobrich, B.; Federici, L.; Gamberini, E.; Gatignon, L.; Guida, R.; Hahn, F.; Holzer, E. B.; Jenninger, B.; Koval, M.; Laycock, P.; Lehmann Miotto, G.; Lichard, P.; Mapelli, A.; Massri, K.; Noy, M.; Palladino, V.; Perrin-Terrin, M.; Pinzino, J.; Ryjov, V.; Schuchmann, S.; Venditti, S.; Bache, T.; Brunetti, M. B.; Duk, V.; Fascianelli, V.; Fry, J. R.; Gonnella, F.; Goudzovski, E.; Iacobuzio, L.; Lazzeroni, C.; Lurkin, N.; Newson, F.; Parkinson, C.; Romano, A.; Sergi, A.; Sturgess, A.; Swallow, J.; Heath, H.; Page, R.; Trilov, S.; Angelucci, B.; Britton, D.; Graham, C.; Protopopescu, D.; Carmignani, J.; Dainton, J. B.; Jones, R. W. L.; Ruggiero, G.; Fulton, L.; Hutchcroft, D.; Maurice, E.; Wrona, B.; Conovaloff, A.; Cooper, P.; Coward, D.; Rubin, P.

doi:10.1007/JHEP11(2020)042

The NA62 experiment reports an investigation of the K+→ π+nu nubar mode from a sample of K+ decays collected in 2017 at the CERN SPS. The experiment has achieved a single event sensitivity of (0.389 ± 0.024) × 10−10, corresponding to 2.2 events assuming the Standard Model branching ratio of (8.4 ± 1.0) × 10−11. Two signal candidates are observed with an expected background of 1.5 events. Combined with the result of a similar analysis conducted by NA62 on a smaller data set recorded in 2016, the collaboration now reports an upper limit of 1.78 × 10−10 for the K+→ π+nu nubar branching ratio at 90% CL. This, together with the corresponding 68% CL measurement of (0.48−0.48+0.72) × 10−10, are currently the most precise results worldwide, and are able to constrain some New Physics models that predict large enhancements still allowed by previous measurements.