Illuminating Dark Sectors with Low-Energy Leptons
Dr. Christian Herwig
FermiLab
Though the range of viable dark matter (DM) masses spans 90 orders of magnitude, the natural scenario where its abundance is set by thermal contact with ordinary matter in the early universe significantly restricts this window to ~MeV to multi-TeV masses. This thermal origin implies an interaction between DM and Standard Model (SM) particles, and thus the rich possibility that it may be produced via accelerated beams.
Despite a broad program of LHC searches for DM candidates above the GeV scale, important blind spots remain for beyond-the-SM particles with compressed mass spectra: a generic feature of many of the simplest DM models. I will discuss how the novel reconstruction of ultra-low-energy leptons with the CMS Experiment are enabling new searches in this space, exploiting events with missing-momentum and low-mass lepton pairs. Even as these searches place the first constraints on these models since LEP, I will demonstrate how the HL-LHC will afford even greater opportunities, contingent on critical upgrades to the CMS tracking and trigger systems. Lastly, I will consider new avenues to probe DM candidates lighter than the proton by adapting LHC techniques and technologies to low-energy, fixed target experiments such as the Light Dark Matter eXperiment (LDMX) at SLAC.