PT Journal
AU NA62 Collaboration (Cortina Gil, Eea
   Husek, T
TI Search for heavy neutral lepton production in K+ decays to positrons
SO Physics Letters B
JI Phys. Lett. B
PY 2020
BP 135599
EP 9pp
VL 807
DI 10.1016/j.physletb.2020.135599
LA English
AB A search for heavy neutral lepton (N) production in K+ -> e(+)N decays using the data sample collected by the NA62 experiment at CERN in 2017-2018 is reported. Upper limits of the extended neutrino mixing matrix element vertical bar U-e4 vertical bar(2) are established at the level of 10(-9) over most of the accessible heavy neutral lepton mass range 144-462 MeV/c(2), with the assumption that the lifetime exceeds 50 ns. These limits improve significantly upon those of previous production and decay searches. The vertical bar U-e4 vertical bar(2) range favoured by Big Bang Nucleosynthesis is excluded up to a mass of about 340 MeV/c(2).
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