Search for heavy neutral leptons in decays of W bosons using leptonic and semi-leptonic displaced vertices in SQUARE ROOTs = 13 TeV pp collisions with the ATLAS detector

Abstract

A search is performed for long-lived heavy neutral leptons (HNLs), producedthrough the decay of a W boson along with a muon or electron. Two channels are explored:a leptonic channel, in which the HNL decays into two leptons and a neutrino, and a semileptonicchannel, in which the HNL decays into a lepton and a charged pion. The search isperformed with 140 fb-1 of SQUARE ROOTs = 13TeV proton-proton collision data collected by ATLASduring Run 2 of the Large Hadron Collider. No excess of events is observed; Dirac-like andMajorana-like HNLs with masses below 14.5 GeV and mixing coefficients as small as 10-7 areexcluded at the 95% confidence level. The results are interpreted under different assumptionson the flavour of the leptons from the HNL decays.