Felix Wagner
PostDoc, Superconducting Quantum Bits and Sensors
I am working on experiments for the direct detection of dark matter and compiled a brief introduction to the field below. A few more details of my projects are listed in the menu under "Projects".
Dark matter
Dark matter is a type of matter that does not interact with light or other forms of electromagnetic radiation, making it invisible to telescopes. However, its presence can be inferred through its gravitational effects on visible matter, such as the rotation curves of galaxies. It is estimated that dark matter makes up approximately 85% of the matter in the universe. No dark matter particle was measured until today, making its nature one of the biggest open questions in modern physics.
Image from https://wmap.gsfc.nasa.gov/universe/uni_matter.html
Direct detection experiments
Direct detection experiments, such as CRESST and COSINUS, aim to detect dark matter particles through their interactions with normal matter. These experiments use detectors made of sensitive materials, such as crystals or scintillating liquids, to detect the tiny amounts of energy released when a dark matter particle collides with an atom in the detector. By studying these interactions, researchers hope to learn more about the properties of dark matter and its role in the universe.
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In the figure left I show the expected scattering rate in an earth-based silicon detector, normalized to the mass of the detector and the runtime of the measurement, for various dark matter masses.
Cryogenic calorimeters with transition edge sensors
Cryogenic calorimeters are a type of detector used in direct detection experiments for dark matter that rely on the measurement of heat produced by the collision of a dark matter particle with the detector. These detectors typically consist of a sensor made of a sensitive material, such as a crystal or scintillating material, that is cooled to extremely low temperatures, typically around 10 millikelvin, to minimize thermal noise. Transition Edge Sensors (TES) are a type of sensor used in these detectors that rely on the measurement of the change in resistance of a thin film of superconducting material when it is exposed to a small amount of heat produced by the collision of a dark matter particle with the detector. TES are highly sensitive and have high energy resolution, making them suitable for detecting low-energy particle interactions.
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There are several specific challenges in detecting dark matter with cryogenic calorimeters and TES.The property dominating the sensitivity of a detector is the energy threshold, i.e. the lowest particle recoil energy that can be detected. To optimize this, the superconducting film is operated in its transition from superconducting to normal conducting state, for that a careful fine tuning of the operation settings is necessary. Ideally, particle recoils in the detector produce pulse-shaped voltage traces in the readout electronics. The shape and amplitude of these pulses needs to be analyzed to discriminate recoils from instrumental artefacts, and recoil energies need to be calibrated. Furthermore, interactions of other particles in the detector (backgrounds) need to be minimized, which is why experiments are usually done in underground laboratories, as e.g. the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, where we do our experiments.
Below I show an transition curve of a TES and an exemplary pulse from a particle recoil.
