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

宇宙中物质的主体是什么，以及为什么物质和反物质之间存在不对称性，这构成了物理学和天文学中两个重要的悬而未决的问题。粒子物理学通过寻找罕见事件来探索答案，包括来自标准模型之外的奇异新暗物质粒子的相互作用，以及涉及中微子的不寻常衰变。长期以来，我一直对这些搜索感兴趣，并为它们开发新的探测器。在接下来的五年里，我和我的团队将在绝对零度以上的温度下测量材料的光学性质，以建立用于罕见事件搜索的改进探测器。例如，Li2MoO4和ZnSe是可能提供难以捉摸的无中微子双β衰变的证据的化合物。掺入放射性元素的NaI闪烁体将提供更好的理解，了解这些探测器如何响应可能是暗物质背景的不同类型的粒子。我们将研究不同温度下的波长移位器，以提高未来稀有液体探测器的能力。我们将研究机械应力如何影响CsI闪烁体的光产额。此外，我们将测试新的光探测器SiPM及其电子设备，温度低至4K，以检测低温闪烁，例如由贵重液体或其他闪烁体中的暗物质粒子引起的闪烁。最后，在这个项目的第一年，我们将总结KDK，这是一个测量钾的罕见衰变的实验，钾是一种自然存在的元素，在许多罕见事件搜索中，钾是放射性背景。钾可能会在理解DAMA合作发现暗物质这一有争议的声明中发挥作用。这项工作将支持加拿大SNOLAB的强大稀有事件搜索计划，并增加下一代300吨规模的贵重液体实验落户那里的机会。在其5年的课程中，该项目将支持和培训5名本科生和4名研究生，并为培养第5名研究生和1名博士后研究员做出贡献，这两人的工资都由麦克唐纳研究所支付。

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.