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

Abstract

This thesis both proposes and experimentally explores the opportunity to operate Transition Edge Sensors (TES) as detectors for Dark Matter (DM)-scattering by simultaneously employing them as target and sensor. By exploiting their microcalorimetric capabilities and sensitivity to low energy depositions, competitive limits can be set on low mass DM interactions based on electron scattering. Further limits on absorption and DM-nucleon scattering 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, the TES sensors are not comparable to large scale experiments searching for ∼GeV-scale Weakly Interacting Massive Particles (WIMPs). However, the sensors’ sensitivity to energy depositions as low as ∼ 0.3 eV enables sensitivity to much lower sub-MeV DM masses. TES are operated on the transition curve between the normal and superconducting state, where the sensor is sensitive to the smallest energy depositions, yielding detectable pulses. Based on the detector’s sensitivity, especially to single near-infrared photons, it should also be sensitive 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 TES detection system, dedicated DM searches were performed with two distinct TES detection modules. In dedicated experimental setups, the well-known ALPS II-optimized analysis scheme was employed to determine ideal detector configurations for DM searches in need of a sufficiently large energy bandwidth. In a next step, the detector’s energy response was investigated by analyzing the pulse shapes of photons from different lasers with photon energies from 0.76 eV to 1.41 eV. During these tests, a linear proportionality between the pulse’s integral with the energy was found, while at the same time, the rise and decay time of the pulses stayed predominantly constant over these energies. This performance along with subsequent simulations of signal pulses over a larger energy range can be used for a dedicated event selection to isolate photon-like pulses from the various backgrounds present in the system. Therefore, these background sources, including fast (baseline) noise spikes, are mitigated by 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 second module TES F with a setup adjusted for DM search measurements is presented in a preliminary analysis, as well. DM search measurements of 489 h and 400 h have been performed, respectively. By applying dedicated event selections to each, limits on different DM parameter spaces have been set for both, considering expected DM interaction rates in the explored DM mass range. The resulting limits are compared to results originating from similar experimental efforts, especially one employing Superconducting Nanowire Single Photon Detectors (SNSPDs) as both target and sensor, as well. The TES modules are able to surpass limits set by the first generation of these SNSPDs for lower masses in the light mediator limit. However, limits set by a dedicated optimized second generation SNSPD experiment exceed both. Nevertheless, this enhancement from a first to a second upgraded generation already exemplifies the strength of such an approach, as similar improvements can be explored for TES detectors as well. Therefore, projections for possible future detection scenarios are explored, presenting the strength of possible second generation TES detection systems. Hence, it was shown for the first time, that TES detectors can be used as a simultaneous sensor and target in direct DM experiments with a plethora of possibilities for further upgrades and optimization.