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Kleimenova, A.; Petrov, Y.; Velghe, B.; Aliberti, R.; Lomidze, D.; Peruzzo, L.; Wanke, R.; Neri, I.; Petrucci, F.; Wahl, H.; Cotta Ramusino, A.; Gianoli, A.; Latino, G.; Bizzeti, A.; Kozhuharov, V.; Lanfranchi, G.; Martellotti, S.; Spadaro, T.; Ambrosino, F.; Corvino, M.; Mirra, M.; Saracino, G.; Brizioli, F.; Imbergamo, E.; Lollini, R.; Piandani, R.; Checcucci, B.; Lupi, M.; Pepe, M.; Piccini, M.; Costantini, F.; Giorgi, M.; Lamanna, G.; Sozzi, M.; Mannelli, I.; D'Agostini, G.; Biagioni, A.; Leonardi, E.; Valente, P.; Vicini, P.; Ammendola, R.; Salamon, A.; Sargeni, F.; Bloch-Devaux, B.; Boretto, M.; Menichetti, E.; Engelfried, J.; Estrada-Tristan, N.; Ghinescu, S.A.; Baeva, A.; Emelyanov, D.; Falaleev, V.; Kekelidze, V.; Litov, L.; Misheva, M.; Molokanova, N.; Potrebenikov, Yu; Shkarovskiy, S.; Zinchenko, A.; Fedotov, S.; Kudenko, Y.; Medvedeva, M.; Kholodenko, S.; Obraztsov, V.; Ostankov, A.; Semenov, V.; Yushchenko, O.; Cerny, V.; Ceccucci, A.; De Simone, N.; Döbrich, B.; Federici, L.; Gamberini, E.; Guida, R.; Jenninger, B.; Koval, M.; Mapelli, A.; Marchevski, R.; Noy, M.; Palladino, V.; Perrin-Terrin, M.; Pinzino, J.; Schuchmann, S.; Brunetti, M.B.; Duk, V.; Goudzovski, E.; Newson, F.; Romano, A.; Sergi, A.; Sturgess, A.; Heath, H.; Trilov, S.; Carmignani, J.; Dainton, J.B.; Ruggiero, G.; Maurice, E.; Wrona, B.; Cooper, P.; Coward, D.; Rubin, P.
Physics letters. B, 05/2021, Volume: 816Journal Article
The NA62 experiment at CERN reports searches for K+→μ+N and K+→μ+νX decays, where N and X are massive invisible particles, using the 2016–2018 data set. The N particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of O(10−8) of the neutrino mixing parameter |Uμ4|2 for N masses in the range 200–384 MeV/c2 and lifetime exceeding 50 ns. The X particle is considered a scalar or vector hidden sector mediator decaying to an invisible final state, and upper limits of the decay branching fraction for X masses in the range 10–370 MeV/c2 are reported for the first time, ranging from O(10−5) to O(10−7). An improved upper limit of 1.0×10−6 is established at 90% CL on the K+→μ+ννν¯ branching fraction.
