Optical characterization of materials at low temperatures for rare-event searches

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What constitutes the bulk of the matter in the universe, and why there is an asymmetry between matter and anti-matter, constitute two important open questions in physics and astronomy. Particle physics explores answers by looking for rare events, including the interactions of exotic new dark-matter particles from beyond the standard model, and unusual decays involving neutrinos. I have a longstanding interest in these searches, and in developing new detectors for them. Over the next five years, my group and I will measure the optical properties of materials at temperatures down to a few degrees above absolute 0 to build improved detectors for rare-event searches. For instance, Li2MoO4 and ZnSe are compounds that may provide evidence of elusive neutrinoless double beta decay. NaI scintillators doped with radioactive elements will provide a better understanding of how these detectors respond to particles of different types that may be a background for dark matter. We will investigate wavelength shifters at various temperatures in order to enhance the capacities of future noble liquid detectors. We will study how mechanical stress affects the light yield of CsI scintillator. Moreover, we will test new light detectors, SiPMs, and their electronics, down to 4 K, to detect low-temperature scintillation, caused for instance by dark matter particles in noble liquids or other scintillators. Lastly, in the first year of this project, we will wrap-up KDK, an experiment to measure a rare decay of potassium, a naturally-occurring element, which is a radioactive background in many rare-event searches. Potassium may play a role in understanding the controversial claim of dark matter discovery by the DAMA collaboration. This work will support the strong rare-event search program at SNOLAB in Canada, and increase the chance that the next generation, 300-ton scale, noble liquid experiments are located there. Over its 5-year course, this program will support and train five undergraduate and four graduate students, and contribute to the training of a fifth graduate student and of a postdoctoral researcher, whose salaries are both paid by the McDonald Institute.