Dark Sectors in Electron Fixed-Target Experiments

Miriam Diamond
University of Toronto

Abstract:

The leading dark matter (DM) paradigm over the past few decades has been that of a Weakly Interacting Massive Particle with a mass of tens of GeV to a few TeV. But in light of recent experimental constraints, attention is increasingly turning to models with lower-mass DM, especially in the context of a “dark sector” featuring multiple DM particle species. Probing such models requires exploiting complementarity between different types of DM searches, where electron-beam fixed-target experiments play an important role in the DM mass range of a few to hundreds of MeV. These experiments seek to generate dark sector particles, such as dark photons, via electron-nucleus scattering and emission processes analogous to standard bremsstrahlung. Identifying the visible decay products of the dark sector particles, such as electron-positron pairs, requires precise reconstruction of narrow mass resonances and/or displaced vertices; accounting for invisible decay products requires precise missing energy and/or momentum measurements. In this talk, I will give an overview of the landscape of current and planned fixed-target DM searches, with the Heavy Photon Search (HPS) and its planned successor LDMX (Light Dark Matter eXperiment) as specific examples.