Demystifying freeze-in dark matter at the LHC

Abstract

Freeze-in mechanism provides robust dark matter production in the early Universe. Because of its feeble interactions, freeze-in dark matter leaves signals at colliders which are often involved with long-lived particle decays and consequent displaced vertices (DV). In this paper, we develop a method to read off mass spectrum of particles being involved in the DV events at the LHC. We demonstrate that our method neatly works under limited statistics, detector resolution, and smearing effects. The signature of DV at the LHC can come from either highly suppressed phase space or a feeble coupling of particle decay processes. By measuring invisible particle mass spectrum, one can discriminate these two cases and thus extract information of dominant freeze-in processes in the early Universe at the LHC.