Lowering Backgrounds and Thresholds in the Search for Light Dark Matter with SuperCDMS

Abstract

Cosmological observations have produced a wealth of evidence which demonstrates that the majority of thematter content in our Universe is “dark”. The identity of this dark matter remains elusive, as none of the members of the standard model of particle physics accurately describe its properties. This has prompted the scientific community to launch a broad search, spanning decades in time, mass and sensitivity, with the goal of detecting and identifying this source of new physics. The next generation of the Super Cryogenic Dark Matter Search (SuperCDMS) is currently under construction deep underground at SNOLAB. The experiment aims to expand the search for dark matter to lower masses (≲ 10 GeV/c2) and greater sensitivities using silicon and germanium detectors by minimizing experimental backgrounds and operating detectors with superb energy resolution. SuperCDMS will accomplish its low projected background in part by deploying a robust shield to protect its detectors from environmental radiation. This dissertation presents the results of simulations which demonstrate the success of the shield design at stopping radiogenic neutrons. The shield will be able to reduce these environmental sources to the point where coherent scattering from solar neutrinos are expected to dominate the nuclear recoil backgrounds. In order to search for such light dark matter masses, SuperCDMS uses sensitive transition edge sensors to measure small energy depositions in the detectors. The ultimate energy resolution of these devices, expected to be < 1 eV, has not yet been realized. This dissertation describes the analysis of a dark matter search performed at the University of Massachusetts Amherst with a prototype detector which uses SuperCDMS style sensors to achieve a baseline energy resolution of 2.3 eV. The results of this search demonstrate sensitivity to dark matter candidates with masses as low as ∼ 25 MeV.