DARWIN: towards the ultimate dark matter detector

Abstract: DARk matter WImp search with liquid xenoN (DARWIN) will be an experiment for the direct detection of dark matter using a multi-ton liquid xenon time projection chamber at its core. Its primary goal will be to explore the experimentally accessible parameter space for Weakly Interacting Massive Particles (WIMPs) in a wide mass-range, until neutrino interactions with the target become an irreducible background. The prompt scintillation light and the charge signals induced by particle interactions in the xenon will be observed by VUV sensitive, ultra-low background photosensors. Besides its excellent sensitivity to WIMPs above a mass of 5 GeV/c2, such a detector with its large mass, low-energy threshold and ultra-low background level will also be sensitive to other rare interactions. It will search for solar axions, galactic axion-like particles and the neutrinoless double-beta decay of 136-Xe, as well as measure the low-energy solar neutrino flux with <1% precision, observe coherent neutrino-nucleus interactions, and detect galactic supernovae. We present the concept of the DARWIN detector and discuss its physics reach, the main sources of backgrounds and the ongoing detector design and R&D efforts.

• The paper presents the design and operational objectives of the DARWIN detector, targeting dark matter detection with sensitivity to spin-independent WIMP-nucleon cross-sections as low as 10⁻⁴⁹ cm².
• It details a multi-ton LXe TPC that leverages dual-phase detection using both scintillation and ionization signals to suppress background and extend detection thresholds to WIMP masses around 5 GeV/c².
• The proposal also outlines complementary physics goals, including searches for axions, precise solar neutrino measurements (<1% precision), and neutrinoless double-beta decay, underscoring its broad scientific impact.

An Analysis of the DARWIN Dark Matter Detector Project

The DARWIN collaboration presents an extensive project proposal aiming at the direct detection of dark matter (DM) through Weakly Interacting Massive Particles (WIMPs) using a multi-ton liquid xenon (LXe) time projection chamber (TPC). The paper outlines the design of the proposed DARWIN experiment, which aims to cover a comprehensive range of WIMP masses and coupling strengths, thereby extending the sensitivity beyond current and near-future detectors.

Technical Design and Operational Objectives

The DARWIN detector is envisioned to include a 50-ton xenon target, concentrating on a multitude of compelling science goals beyond WIMP detection, such as searches for axions and axion-like particles, neutrino physics, and the neutrinoless double-beta decay process. The detector design builds upon successful concepts deployed in existing LXe-based detectors but scales the target volume significantly to reach unprecedented sensitivities.

Dark Matter Sensitivity and Investigation of Parameter Spaces

The primary goal is to explore the parameter space accessible for WIMPs, particularly targeting spin-independent WIMP-nucleon cross-sections as low as $10^{-49}$ cm². To achieve this, the DARWIN detector will leverage its large target volume and low background environment. The proposal discusses potential configurations for the dual-phase TPC system, which utilize both prompt scintillation (S1) and ionization (S2) signals for event discrimination and background suppression. The target mass and design specifications are carefully chosen to push the detection thresholds, ensuring sensitivity down to lower WIMP masses around 5 GeV/$c^2$.

Complementary Physics Targets

In addition to dark matter searches, DARWIN’s sizable LXe mass and ultra-low background will enable investigations into other rare processes. This includes solar axions, galactic supernova neutrinos, coherent neutrino-nucleus scattering, and potentially neutrinoless double-beta decay searches utilizing $^{136}$Xe. The experiment aims to measure solar neutrino fluxes with unprecedented precision (<1%) and to collect real-time data during supernova events, enriching our understanding of neutrino properties and interactions.

Background Mitigation Techniques

The paper describes comprehensive strategies for background mitigation, which are crucial for reaching DARWIN's sensitivity goals. The internal radioactivity will be minimized by careful selection of low-radioactivity materials and advanced techniques such as cryogenic distillation to eliminate krypton contamination. Active and passive shielding structures, robust purification systems, and high-purity construction materials are foreseen to suppress both external and intrinsic backgrounds to the required levels.

Technological Challenges and R&D Efforts

Recognizing the technological challenges inherent in scaling up TPC and cryogenic systems, the collaboration dedicates significant resources to research and development. This includes innovations in high-voltage systems, new photo-detection technologies like silicon photomultipliers and gaseous photomultipliers, and advanced data acquisition systems capable of coping with the increased channel count and data rates associated with a detector of this scale.

Outlook and Implications

The DARWIN project represents a significant advancement in direct dark matter detection technologies, with implications that extend into broader fields of particle astrophysics and neutrino physics. Through its extensive program of rare event searches, DARWIN is poised to provide vital insights, irrespective of whether or not a WIMP signal is observed within its sensitivity range. The collaboration anticipates operational readiness by the mid-2020s, aligning with the broader timeline of strategic underground physics initiatives.

In conclusion, the DARWIN proposal articulates a well-considered, multifaceted approach to next-generation dark matter searches, infusing the endeavor with a breadth that extends into several complementary science goals. The planned advancements in detection capabilities and background reduction methodology could decisively influence the trajectory of dark matter and neutrino research in the coming decades. Such an ambitious project underscores a collaborative ethos in astroparticle physics, setting a strategic benchmark for future experiments in this domain.