High-energy proton collisions can be used to study heavy particles that decay very quickly, like the Higgs boson. But long-lived particles – which travel more than a few millimeters before they decay – could be escaping traditional search strategies focused on particles with short lifetimes. Taking on the challenge of designing novel search techniques for particles that decay away from the proton collision point has enormous potential, since many theories point to long-lived particles as solutions to big questions we have about our Universe. For example, long-lived heavy neutrinos provide a natural way to generate light neutrino masses, explain the observed matter-antimatter asymmetry and even provide a dark matter candidate.

In this talk I will present a case study of the unique experimental approaches used to hunt for long-lived heavy neutrinos using data collected by the ATLAS experiment. This talk will also discuss the landscape of heavy neutrino searches at the Large Hadron Collider (LHC) and new directions which can be explored with the current data and the data that will be collected at the high-luminsoity LHC.