Physics beyond the Standard Model with NA62

Abstract

The NA62 experiment at CERN took data in 2016–2018 with the main goal of measuring the K + → νν̅ decay. The NA62 dataset is also exploited to search for light feebly interacting particles produced in kaon decays. Searches for K + → e + N and K + → μ + N decays, where N is a massive invisible particle, are performed. The N particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of 𝒪(10-8) the neutrino mixing parameter |U14|2, where l = e,μ. Dedicated trigger lines were employed to collect di-lepton final states, which allowed stringent upper limits to be established for the rates lepton flavor and lepton number violating kaon decays. Upper limits on the rates of several K + decays violating lepton flavour and lepton number conservation, obtained by analysing this dataset, are presented here.