Search for K+ decays to a muon and invisible particles

The NA62 Collaboration

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48 Citations (Scopus)


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.

Original languageEnglish
Article number136259
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Publication statusPublished - 10 May 2021

Bibliographical note

Funding Information:
The cost of the experiment and its auxiliary systems was supported by the funding agencies of the Collaboration Institutes. We are particularly indebted to: F.R.S.-FNRS ( Fonds De La Recherche Scientifique - FNRS ), Belgium; BMES ( Ministry of Education Youth and Science, Bulgaria ); NSERC (Natural Sciences and Engineering Research Council), funding SAPPJ-2018-0017 Canada; NRC (National Research Council) contribution to TRIUMF , Canada; MEYS (Ministry of Education, Youth and Sports), Czech Republic; BMBF (Bundesministerium für Bildung und Forschung) contracts 05H12UM5 , 05H15UMCNA and 05H18UMCNA , Germany; INFN (Istituto Nazionale di Fisica Nucleare), Italy; MIUR (Ministero dell'Istruzione, dell'Università e della Ricerca), Italy; CONACYT (Consejo Nacional de Ciencia y Tecnología), Mexico; IFA (Institute of Atomic Physics) Romanian CERN-RO No. 1/16.03.2016 and Nucleus Programme PN 19 06 01 04 , Romania; INR-RAS (Institute for Nuclear Research of the Russian Academy of Sciences), Moscow, Russia; JINR (Joint Institute for Nuclear Research), Dubna, Russia; NRC (National Research Center) “Kurchatov Institute” and MESRF ( Ministry of Education and Science of the Russian Federation ), Russia; MESRS ( Ministry of Education, Science, Research and Sport ), Slovakia; CERN (European Organization for Nuclear Research), Switzerland; STFC (Science and Technology Facilities Council), United Kingdom; NSF (National Science Foundation) Award Numbers 1506088 and 1806430 , U.S.A.; ERC ( European Research Council ) “UniversaLepto” advanced grant 268062 , “KaonLepton” starting grant 336581 , Europe.

Funding Information:
Individuals have received support from: Charles University Research Center ( UNCE/SCI/013 ), Czech Republic; Ministry of Education, Universities and Research (MIUR “Futuro in ricerca 2012” grant RBFR12JF2Z , Project GAP), Italy; Russian Foundation for Basic Research (RFBR grants 18-32-00072 , 18-32-00245 ), Russia; Russian Science Foundation (RSF 19-72-10096 ), Russia; the Royal Society (grants UF100308 , UF0758946 ), United Kingdom; STFC (Rutherford fellowships ST/J00412X/1 , ST/M005798/1 ), United Kingdom; ERC (grants 268062 , 336581 and starting grant 802836 “AxScale”); EU Horizon 2020 (Marie Skłodowska-Curie grants 701386 , 842407 , 893101 ).

Publisher Copyright:
© 2021 The Author(s)


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