Direct dark matter searches offer an extraordinary opportunity to unravel one of the greatest enigmas of our universe. The most common strategy is the search for elastic spin-independent dark-matter–nucleus scattering, which would produce tiny nuclear recoils in sensitive detectors. At the same time, many experiments are also sensitive to alternative dark-matter candidates and interaction channels, including particles such as axion-like particles (ALPs) or dark photons. Because the expected interaction rate is extremely small, these experiments must achieve ultra-low background levels. Consequently, they are typically operated in deep underground laboratories to shield them from cosmic radiation and rely on highly radiopure detector materials and careful background mitigation techniques. Different experimental approaches are optimized for different regions of the dark-matter parameter space. For instance, the CRESST experiment and the upcoming DELight experiment employ cryogenic calorimeters with exceptionally low energy thresholds, making them particularly sensitive to light dark matter in the sub-GeV mass range. In contrast, experiments such as XENONnT and the planned XLZD use dual-phase xenon time-projection chambers and focus on the more traditional GeV–TeV dark-matter mass range, where they excel among others due to their very large target masses.
The DELight experiment (Direct search Experiment for Light dark matter) is a new experiment currently in the planning and design phase, while simultaneously collecting R&D data. The noble gas helium-4 serves as the active target. Due to its low nuclear mass, it is particularly well-suited for the search for light dark matter being a light scattering partner and thus providing a measurable nuclear recoil signal.
DELight will be equipped with “Large-Area cryogenic MicroCALorimeters” (LAMCALs), which are based on ultra-sensitive energy detectors known as magnetic microcalorimeters (MMCs). These measure the three distinguishable signal channels produced by the recoil of the helium nuclei: phonons/rotons, photons, and helium excimers. In a nuclear recoil, a significantly larger fraction of the energy is transferred to phonons and rotons than in an electron recoil, which makes it possible to distinguish between the two signatures and thus suppress the background, which consists mainly of electron scattering.
In my team, we are working on comprehensive simulation studies to maximize the detector’s efficiency and sensitivity by optimizing the geometry and through a detailed understanding of background events and signal production in superfluid helium. In parallel, my team is developing the data acquisition and trigger system with the goal of achieving a dead-time-free system with the lowest possible detection threshold. In Heidelberg, we work closely with the group of Prof . Dr. Christian Enss at KIP, which is developing the helium cell and cryogenic platform for DELight.
The CRESST experiment (Cryogenic Rare Event Search with Superconducting Thermometers) is a cutting-edge direct detection dark matter experiment utilizing cryogenic detectors. CRESST aims to detect dark matter particles, specifically Weakly Interacting Massive Particles (WIMPs), by using scintillating crystals, made in the default configuartion from calcium tungstate (CaWO4) and operated at millikelvin temperatures. This experimental setup allows for the precise measurement of energy deposited by potential dark matter interactions.
CRESST detectors are equipped with superconducting transition-edge sensors (TES), which measure both phonon (heat) and scintillation light signals produced by particle interactions within the crystals. This dual-signal approach helps in distinguishing between different types of interactions, thereby enhancing the experiment's sensitivity to potential dark matter signals.
Each CRESST detector module consists of a ~25g CaWO4 crystal coupled to a light detector. When a particle interacts with the crystal, it produces a small amount of heat and scintillation light. The heat is measured by the TES, while the light is detected by a separate light detector. The ratio of the phonon to light signal helps differentiate between nuclear recoils (possible dark matter interactions) and electron recoils (background events).
The CRESST experiment is located at the Gran Sasso National Laboratory (LNGS) in Italy, benefiting from the lab's deep underground environment which significantly reduces cosmic ray background noise. This low-background setting, combined with the high sensitivity of cryogenic detectors, enables CRESST to explore new parameter space in the search for dark matter.
For analyses very close to a low energy threshold, a detailed understanding of the raw data and the causes of, and influences on, the noise baseline is of utmost relevance. My group is therefore particularly concerned with the analysis of raw data. One focus here is the development of algorithms based on machine learning. In preparation for a large-scale expansion of CRESST, existing AI algorithms will also be further developed for automated data processing.
The XENONnT experiment is a leading direct detection dark matter experiment operated at the Gran Sasso National Laboratory (LNGS) in Italy. It is part of the XENON program and aims to detect dark matter particles, in particular Weakly Interacting Massive Particles (WIMPs) with masses above about 6 GeV, through their rare interactions with xenon atoms. The experiment is located deep underground to reduce background events from cosmic radiation.
XENONnT employs a large dual-phase (liquid–gas) xenon time projection chamber (TPC) containing several tonnes of ultra-pure liquid xenon, of which about 5.9 tonnes serve as the active target. Xenon is well suited for GeV to TeV-scale dark matter searches due to its high nuclear mass, increasing the probability of an interaction, and its ability to produce both scintillation light and ionization signals when particles interact with it.
The detector measures two distinct signal channels: a prompt scintillation signal and a delayed ionization signal. When a particle interacts in the liquid xenon, it produces an initial flash of scintillation light and ionization electrons. These electrons are drifted upwards in an electric field and extracted into the gaseous phase, where they generate a second light signal. The combination of both signals allows for precise reconstruction of the deposited energy and interaction position, as well as discrimination between nuclear recoils (possible dark matter signals) and electron recoils (background events).
XLZD (short for XENON, LUX-Zeplin and DARWIN) is a coordinated effort to develop the next generation liquid xenon dark matter experiment. It aims to combine the expertise and technologies of current leading collaborations to realize a multi-tens-of-tonne detector with unprecedented sensitivity reaching into the so-called neutrino-fog, the signal region of coherent elastic neutrino-nucleus scattering (CEvNS) measurements.
My team focuses primarily on computing within XENONnT and the data acquisition system for XLZD. In Heidelberg, we are working closely together with the team of Prof. Dr. Stephanie Hansmann-Menzemer at PI and are in regular exchange with the group of Prof. Dr. Teresa Marrodán Undagoitia at MPIK.
Under this link you will find a selection of my and our most relevant journal publications.
