Das DELight Experiment

Dark Matter (DM) is a well-established concept in particle physics, astrophysics and cosmology and a key parameter in the Lambda Cold Dark Matter (ΛCDM) model of Big Bang cosmology. A fit of the ΛCDM model to the power spectrum of the cosmic microwave background (CMB) anisotropies predicts that DM constitutes about 85% of all matter in the Universe. Still, although there is compelling evidence for DM, its nature is unknown and DM particles have yet to be discovered. A great variety of theoretical DM particle candidates exists, spanning many orders of magnitude in mass and coupling strength. Ongoing and planned experiments are only sensitive to a subset of these candidates, one of which being the so-called weakly-interacting massive particle (WIMP) with mass and coupling(s) around the weak scale, produced in the early Universe in thermal equilibrium. Experimental efforts to detect WIMPs include direct detection experiments, designed to measure WIMP scattering off nuclei in the laboratory. Those searches have not discovered the WIMP to date, but have excluded most simple WIMP models with DM masses close to the weak scale.

One possible explanation is that DM is lighter than predicted by the standard WIMP paradigm and well below masses of a few GeV, a possibility that is currently the subject of much theoretical and experimental interest. This WIMP-like sub-GeV DM particle candidate is commonly referred to as Light DM (LDM) and its potential couplings to standard matter have been barely probed by direct detection experiments thus far. The signal resulting from DM scattering off nuclei at such low masses is too small to be observed in typical direct DM search experiments and new detector concepts have to be developed to gain the necessary sensitivity. The Direct search Experiment for Light DM, DELight, will be built to thoroughly explore the LDM region well below the GeV mass scale in DM-nucleus scattering searches.

The first phase of the DELight experiment will consist of a 10L volume of superfluid helium instrumented by Magnetic MicroCalorimeter (MMC) detectors. Above the superfluid helium volume is vacuum. Quasiparticles from particle interactions can liberate helium atoms at the helium surface in a process known as quantum evaporation. The atoms are subsequently detected by MMC detectors positioned above the liquid surface where the MMCs are also sensitive to UV photons. About four fifths of the wafer calorimeters will be submerged in the superfluid also to measure UV photons as well as the long-lived triplet excimers.

Read more about DELight at the experiment´s homepage as well as here.