DELight: Low-background environment

• Applicant: Professor Dr. Marc Schumann
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 561595909

DELight is a new particle physics experiment to search for light dark matter (LDM) particles with masses well below 1 GeV/c2 by detecting elastic LDM scattering off a cryogenic liquid helium (LHe) target. Its low mass number, the low threshold achievable with large-area magnetic microcalorimeters (MMCs), its intrinsic radiopurity and the availability of several signal channels render LHe an ideal target for LDM searches. DELight can only be realized through the confluence of its six projects. Each project plays a fundamental and unique role, where this project is responsible for ensuring that the DELight background level is sufficiently low for a competitive search for LDM. The science goal of the first phase (phase-I) of DELight, to be completed within the first four years of funding, is to search for light dark matter with masses >~60 MeV/c2 with a 1 kg x d exposure of its LHe target and a 20 eV detector threshold, i.e., very close to the He atomic excitation threshold of 19.82 eV. New parameter space with cross sections below 1e-39 cm2 for spin-independent dark matter-nucleon scattering will be explored. The second phase (phase-II) aims for an even lower threshold and a 100 x larger exposure to improve the sensitivity by two orders of magnitude and to explore even lower dark matter masses. The sensitivity predictions currently assume a simplified background scenario, based on preliminary studies. Given that background sources are ubiquitous, with background events coming from the environment (gamma-radiation, neutrons, muons, muon-induced backgrounds) and from the detector and shielding materials themselves (alpha/beta/gamma-radiation, neutrons), the construction of DELight requires low-background technologies and employing various background mitigation strategies. The task of this project within the research unit is to ensure that the background requirements will be reached for phase-I while preparing for the subsequent phase-II. This will be achieved by identifying low-background materials to construct the detector and auxiliary systems close to the LHe target and by studying and developing massive radiation shields to reduce environmental backgrounds. This project will also establish the DELight background model in the underground laboratory, which serves as a crucial input for the dark matter search. A detailed simulation of the DELight detector, to be developed within this project, is the basis for these tasks.

• DFG Programme: Research Units
• Subproject of: FOR 6006: DELight: Direct Search Experiment for Light Dark Matter with Superfluid Helium
• Co-Investigators: Dr. Klaus Eitel; Professor Dr. Christian Walter Dietrich Enss; Dr. Sebastian Lindemann