Search for heavy neutral lepton (HNL) production and lepton flavor and number violation (LFV/LNV) in charged kaon decays using the data collected by Kaon experiment NA62 at CERN are reported.
Upper limits are established on the elements of the extended neutrino mixing matrix for heavy neutral lepton mass in the range 130-450 MeV, improving on the results from previous HNL production search.
The progress and prospects in different LNV/LFV analysis on data sets
from 2015-2018 are reviewed.