Searching for Hidden-Sector Heavy Neutral Leptons

We explore how well existing collider searches for heavy neutral leptons (HNLs) cover a model where HNLs are produced via the decay of a Higgs boson, either directly or through an intermediate Dark Higgs boson. We use MadGraph5_aMC@NLO 3.6.3 and Pythia 8.3 to produce Monte Carlo simulations of HNL productions and decays using this model, then apply selections from existing searches to determine their sensitivity to our model. We place a 95% confidence level limit on the branching ratio of Higgs boson decays to HNLs for HNL masses ranging from 5 to 60 GeV for direct decays, and 2.5 to 20 GeV for decays mediated by a Dark Higgs.