Review of accelerator-based searches for Neutral Long-Lived Particles

Abstract

In this paper we present the current status of searches for neutral long-lived particles. The basic formalism that allows the determination of the number of expected long-lived particles is presented. Heavy neutral leptons can be a type of long-lived particles. The main observational motivations for the existence of heavy neutral lepton is covered as well. A summary of the main results from both collider searches and fixed target/beam dump experiments is presented. The outlook for next generation experiments and their impact on the parameter space of coupling strength and mass of heavy neutral leptons is also discussed.