Exploring light dark matter at accelerators

Abstract

The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. Specific scenarios for a thermal origin of dark matter sharpen this mass range to within about an MeV to 100 TeV. Most of the stable constituents of known matter have masses in the MeV to GeV range, and a thermal origin for dark matter works in a simple and predictive manner in this mass range as well, yet it remains largely unexplored. The simplest and most popular models of sub-GeV dark matter involve a new hypothetical vector boson called a dark (or heavy) photon which provides clear benchmarks for such models. Two fixed target experiments that utilize an electron beam and offer complimentary searches for dark photons are the Heavy Photon Search (HPS) at Jefferson Lab and the planned next generation Light Dark Matter eXperiment (LDMX) at SLAC. HPS searches for visibly decaying dark photons through two distinct methods − a resonance search in the e⁺e⁻ invariant mass distribution and a displaced vertex search for long-lived dark photons − while LDMX will search for invisibly decaying dark photons through a missing-momentum experiment. In this talk, a theoretical motivation for sub-GeV dark matter, an overview of these experiments and their challenges, and the latest results from HPS will be presented.