Light Dark Matter eXperiment: A Discovery Experiment for Sub-GeV Dark Matter

Abstract: 

Nearly a century after first observing dark matter, we have an impressive understanding of its astronomical and cosmological properties but remarkably little knowledge of its fundamental nature. One leading paradigm postulates new fundamental particles that were in thermal equilibrium with ordinary matter in the early universe – thermal relics – where the most familiar example is a new particle that interacts through the weak nuclear force, weakly interacting massive particles (WIMPs).  As searches for WIMPs approach fundamental sensitivity limits, interest in the more general class of thermal relics has emerged, where these dark matter candidates give rise to clear and testable predictions in small, accelerator-based experiments. The Light Dark Matter eXperiment (LDMX) — proposed to operate in End Station A at SLAC using LCLS-II drive beam — is uniquely capable of searching for sub-GeV thermal relics that can explain the observed dark matter abundance. In this talk, I will review the motivations for these searches, describe how the LDMX experiment works, and discuss its potential to discover thermal relic dark matter.