Exploring Potential: ALPS II’s TES Detection System for Direct Dark Matter Searches

AbstractThis thesis both proposes and experimentally explores the opportunity to operate TransitionEdge Sensors (TES) as detectors for Dark Matter (DM)-scattering by simultaneouslyemploying them as target and sensor. By exploiting their microcalorimetric capabilitiesand sensitivity to low energy depositions, competitive limits can be set on low mass DMinteractions based on electron scattering. Further limits on absorption and DM-nucleonscattering can be determined as well.With a sensitive area of 25 μm × 25 μm, 20 nm thickness, and a mass of just 0.2 ng, theTES sensors are not comparable to large scale experiments searching for ∼GeV-scaleWeakly Interacting Massive Particles (WIMPs). However, the sensors’ sensitivity to energydepositions as low as ∼ 0.3 eV enables sensitivity to much lower sub-MeV DM masses. TESare operated on the transition curve between the normal and superconducting state, wherethe sensor is sensitive to the smallest energy depositions, yielding detectable pulses. Basedon the detector’s sensitivity, especially to single near-infrared photons, it should also besensitive to sub-MeV to high MeV DM particles scattering in its electron or nucleon systems.By exploiting the similarity of these processes and using the ALPS II experiment’s TESdetection system, dedicated DM searches were performed with two distinct TES detectionmodules.In dedicated experimental setups, the well-known ALPS II-optimized analysis scheme wasemployed to determine ideal detector configurations for DM searches in need of a sufficientlylarge energy bandwidth. In a next step, the detector’s energy response was investigatedby analyzing the pulse shapes of photons from different lasers with photon energies from0.76 eV to 1.41 eV. During these tests, a linear proportionality between the pulse’s integralwith the energy was found, while at the same time, the rise and decay time of the pulsesstayed predominantly constant over these energies. This performance along with subsequentsimulations of signal pulses over a larger energy range can be used for a dedicated eventselection to isolate photon-like pulses from the various backgrounds present in the system.Therefore, these background sources, including fast (baseline) noise spikes, are mitigatedby dedicated analysis and straightforward cutting schemes.Dedicated DM search measurements are performed using two different detector modules.The measurement and analysis pipeline was optimized for module TES D. A secondmodule TES F with a setup adjusted for DM search measurements is presented in apreliminary analysis, as well. DM search measurements of 489 h and 400 h have beenperformed, respectively. By applying dedicated event selections to each, limits on differentDM parameter spaces have been set for both, considering expected DM interaction rates invthe explored DM mass range. The resulting limits are compared to results originating fromsimilar experimental efforts, especially one employing Superconducting Nanowire SinglePhoton Detectors (SNSPDs) as both target and sensor, as well. The TES modules are ableto surpass limits set by the first generation of these SNSPDs for lower masses in the lightmediator limit. However, limits set by a dedicated optimized second generation SNSPDexperiment exceed both. Nevertheless, this enhancement from a first to a second upgradedgeneration already exemplifies the strength of such an approach, as similar improvementscan be explored for TES detectors as well. Therefore, projections for possible futuredetection scenarios are explored, presenting the strength of possible second generation TESdetection systems. Hence, it was shown for the first time, that TES detectors can be used asa simultaneous sensor and target in direct DM experiments with a plethora of possibilitiesfor further upgrades and optimization.