The Light Dark Matter eXperiment, LDMX
The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range.
Specific scenarios for the origin of dark matter sharpen the focus on a narrower range of masses: the natural scenario where dark matter originates from thermal contact with familiar matter in the early Universe requires the dark matter mass to lie within about an MeV to 100 TeV.
Considerable experimental attention has been given to exploring Weakly Interacting Massive Particles in the upper end of this range (few GeV – ~TeV), while the region ~MeV to ~GeV is largely unexplored. Most of the stable constituents of known matter have masses in this lower range, tantalizing hints for physics beyond the Standard Model have been found here, and a thermal origin for dark matter works in a simple and predictive manner in this mass range as well. It is therefore a priority to explore.
If there is an interaction between light DM and ordinary matter, as there must be in the case of a thermal origin, then there necessarily is a production mechanism in accelerator-based experiments.
The most sensitive way to search for this production is to use a primary electron beam to produce dark matter in ﬁxed-target collisions.
LDMX  has unique sensitivity to light dark matter by exploring such reactions, its reach goes far beyond the predictions from what is predicted by the dark matter abundance in the Universe, and for natures of dark matter particles that are not reachable by direct detection experiments.
LDMX requires a primary electron beam with low current and high duty cycle to collect 1014-1016 electrons on target. This will be provided by the LCLS-II accelerator at the National Accelerator Laboratory SLAC at Stanford . An even more performant beam for a second stage, have been proposed for CERN .
Lund University has central roles in the collaboration as co-spokesperson and experimental physics coordinator, and as contributor to the realization of its hadronic calorimeter, HCal. We also contribute to its computing using the LUNARC computing centre at our university, and our e-science expertise have introduced a distributed computing system for the whole collaboration.
Lund University in LDMX is supported through the Knut & Alice Wallenberg foundation project Light Dark Matter , through the Crafoord foundation  and through the Royal Physiographic Society . The computing is supported by the Swedish National Infrastructure for Computing, SNIC .
The interaction strength between dark matter and Standard Model matter versus the possible mass of the dark matter particles. The black lines show the interaction strength compatible with the dark matter abundance in the universe, and for the types of dark matter particles that are not excluded from analysis of the Cosmic Microware Background. The grey area shows the already excluded region. The coloured lines show the reach of LDMX. The plot is taken from .
Official LDMX website: Light Dark Matter Experiment - Light Dark Matter Experiment - SLAC Confluence
The Wallenberg Project Light Dark Matter
 SLAC beam: https://arxiv.org/abs/1801.07867
 CERN beam: https://arxiv.org/abs/2009.06938
 Knut & Alice Wallenberg foundation: https://kaw.wallenberg.org/en/research-projects-2019
 Crafoord foundation: https://www.crafoord.se/
 Royal Physiographic Society: https://www.fysiografen.se/en/
 Swedish National Infrastructure for Computing, SNIC: https://www.snic.se/
 T. Akesson et al.,Dark Sector Physics with a Primary Electron Beam Facility at CERN,tech. rep., CERN-SPSC-2018-023. SPSC-EOI-018, 2018, URL: http://cds.cern.ch/record/2640784