SuperCDMS HVeV Run 2 Low-Mass Dark Matter Search, Highly Multiplexed Phonon-Mediated Particle Detector with Kinetic Inductance Detector, and the Blackbody Radiation in Cryogenic Experiments

Citation

Chang, Yen-Yung (2023) SuperCDMS HVeV Run 2 Low-Mass Dark Matter Search, Highly Multiplexed Phonon-Mediated Particle Detector with Kinetic Inductance Detector, and the Blackbody Radiation in Cryogenic Experiments. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/jswx-ad33. https://resolver.caltech.edu/CaltechTHESIS:05212023-152144355

Abstract

There is ample evidence of dark matter (DM), a phenomenon responsible for ≈ 85% of the matter content of the Universe that cannot be explained by the Standard Model (SM). One of the most compelling hypotheses is that DM consists of beyond-SM particle(s) that are nonluminous and nonbaryonic. So far, numerous efforts have been made to search for particle DM, and yet none has yielded an unambiguous observation of DM particles.

We present in Chapter 2 the SuperCDMS HVeV Run 2 experiment, where we search for DM in the mass ranges of 0.5--10⁴ MeV/c² for the electron-recoil DM and 1.2--50 eV/c² for the dark photon and the Axion-like particle (ALP). SuperCDMS utilizes cryogenic crystals as detectors to search for DM interaction with the crystal atoms. The interaction is detected in the form of recoil energy mediated by phonons. In the HVeV project, we look for electron recoil, where we enhance the signal by the Neganov-Trofimov-Luke effect under high-voltage biases. The technique enabled us to detect quantized e⁻h⁺ creation at a 3% ionization energy resolution. Our work is the first DM search analysis considering charge trapping and impact ionization effects for solid-state detectors. We report our results as upper limits for the assumed particle models as functions of DM mass. Our results exclude the DM-electron scattering cross section, the dark photon kinetic mixing parameter, and the ALP axioelectric coupling above 8.4 x 10⁻³⁴ cm², 3.3 x 10⁻¹⁴, and 1.0 x 10⁻⁹, respectively.

Currently every SuperCDMS detector is equipped with a few phonon sensors based on the transition-edge sensor (TES) technology. In order to improve phonon-mediated particle detectors' background rejection performance, we are developing highly multiplexed detectors utilizing kinetic inductance detectors (KIDs) as phonon sensors. This work is detailed in chapter 3 and chapter 4. We have improved our previous KID and readout line designs, which enabled us to produce our first ø3" detector with 80 phonon sensors. The detector yielded a frequency placement accuracy of 0.07%, indicating our capability of implementing hundreds of phonon sensors in a typical SuperCDMS-style detector. We detail our fabrication technique for simultaneously employing Al and Nb for the KID circuit. We explain our signal model that includes extracting the RF signal, calibrating the RF signal into pair-breaking energy, and then the pulse detection. We summarize our noise condition and develop models for different noise sources. We combine the signal and the noise models to be an energy resolution model for KID-based phonon-mediated detectors. From this model, we propose strategies to further improve future detectors' energy resolution and introduce our ongoing implementations.

Blackbody (BB) radiation is one of the plausible background sources responsible for the low-energy background currently preventing low-threshold DM experiments to search for lower DM mass ranges. In Chapter 5, we present our study for such background for cryogenic experiments. We have developed physical models and, based on the models, simulation tools for BB radiation propagation as photons or waves. We have also developed a theoretical model for BB photons' interaction with semiconductor impurities, which is one of the possible channels for generating the leakage current background in SuperCDMS-style detectors. We have planned for an experiment to calibrate our simulation and leakage current generation model. For the experiment, we have developed a specialized ``mesh TES'' photon detector inspired by cosmic microwave background experiments. We present its sensitivity model, the radiation source developed for the calibration, and the general plan of the experiment.

Thesis Files