LDMX

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 [1] 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 [2]. An even more performant beam for a second stage, have been proposed for CERN [3].

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 [4], through the Crafoord foundation [5] and through the Royal Physiographic Society [6]. The computing is supported by the Swedish National Infrastructure for Computing, SNIC [7].