Deep Underground Science and Engineering Lab: Dark Matter Working Group 2007 White Paper

This whitepaper is the result of discussions and presentations initiated at the DUSEL Town Meeting held in Washington in November 2007. The essential elements of this report are: - The quest to detect dark matter is a science goal of the very highest priority, and is flagship science for DUSEL. - The dark matter community presents here a Roadmap for a set of proposals for the Initial Suite of Experiments. The science goals will be reached in two phases of experiments, at the 4850 and 7400 ft levels, respectively. - The US is currently the world leader in the search for WIMP dark matter. Constructing DUSEL will ensure that the US will continue its leading role and attract international collaborators to DUSEL.

💡 Research Summary

The 2007 DUSEL Dark Matter Working Group white paper, drafted after the Washington town‑meeting, positions the search for dark matter as the flagship scientific mission of the Deep Underground Science and Engineering Laboratory (DUSEL). It argues that the United States, currently the world leader in Weakly Interacting Massive Particle (WIMP) searches, must secure a deep‑underground laboratory to maintain this leadership and to attract a broad international community. The document outlines a two‑phase experimental roadmap, each tied to a specific depth within the proposed underground complex: the 4,850‑ft (≈1.5 km) level for an “Initial Suite” of experiments, followed by a more ambitious program at the 7,400‑ft (≈2.2 km) level.

Phase I focuses on deploying a set of mature detector technologies that can be built and commissioned relatively quickly. The plan includes liquid noble‑gas time projection chambers (LXe, LAr, LKr), cryogenic solid‑state detectors (Ge, Si), and bubble‑chamber style experiments. The primary scientific goal is to probe WIMP‑nucleon cross sections down to ~10⁻⁴⁶ cm², matching the best limits achieved worldwide, while reducing background rates to ≤10⁻⁴ counts per day per kg per keV. Achieving these targets requires rigorous material screening, extensive passive shielding, active veto systems, and real‑time calibration to control cosmogenic muon fluxes and radiogenic neutrons.

Phase II, situated at the deeper 7,400‑ft level, is designed to push sensitivity an order of magnitude further, toward cross sections of ~10⁻⁴⁸ cm². This phase envisions ton‑scale liquid xenon detectors, multi‑detector arrays, and next‑generation cryogenic bolometers. Lessons learned from Phase I will be applied: ultra‑pure detector media, improved thermal management to suppress phonon noise, and sophisticated data‑analysis pipelines that employ machine‑learning classifiers for signal‑background discrimination. The deeper site dramatically attenuates muon‑induced backgrounds, enabling the ultra‑low background environment required for such extreme sensitivities.

Beyond the technical roadmap, the paper stresses the strategic importance of DUSEL as a hub for interdisciplinary collaboration. It proposes a governance model that integrates U.S. national laboratories, university groups, and international partners, fostering shared responsibility for detector design, construction, and data analysis. An explicit emphasis is placed on training the next generation of scientists and engineers, with dedicated graduate‑student programs, post‑doctoral fellowships, and technology‑transfer pathways to industry.

Budgetary considerations are addressed through a modular funding strategy: Phase I requires a relatively modest capital outlay, allowing early scientific returns and a proof‑of‑concept that can be leveraged to secure additional investment for Phase II. The authors also outline risk‑mitigation measures, including staged construction, redundancy in critical systems, and compliance with safety and environmental regulations.

In summary, the white paper presents a compelling case that DUSEL, by providing deep‑underground space at two distinct depths, will enable the United States to maintain its leadership in dark‑matter research, achieve world‑leading sensitivities, and cultivate a vibrant, internationally collaborative scientific ecosystem. The proposed roadmap balances immediate feasibility with long‑term ambition, ensuring that each experimental phase builds on the successes and lessons of its predecessor while steadily advancing toward the ultimate goal of a definitive detection of particle dark matter.