CAREER: R&D for Future Noble-Liquid-Based Dark Matter Searches: Hybrid Photosensors and Intrinsic Background Rejection

多个天文观测已经确定，宇宙中大约85%的物质不是由已知粒子组成的。破译这种所谓的暗物质（DM）的性质对于宇宙学，天体物理学和高能粒子物理学具有根本的重要性。在过去的十年里，我们对DM存在的了解有了显著的增长，主要是通过观察它的引力影响。然而，一些基本问题仍然没有得到解决：DM是一种粒子吗？DM的种类不止一种吗？它是否通过非引力相互作用？我们正在系统地寻找DM，并仔细检查其检测的声明，但迄今为止，还没有人报告结论性的DM信号。这迫使我们扩大搜索范围，并开发能够使测量比目前可用的更敏感的数量级的技术。直接DM探测实验旨在测量DM在探测器中散射原子时所沉积的能量。其中，基于贵族液体的实验目前处于领先地位，预计到本十年末，DM搜索的灵敏度将提高两个数量级。为了实现这一目标，实验在很大程度上依赖于增加目标质量和实现非常低的背景环境。目前这一代的贵液DM探测器受到探测器材料、光电倍增管（PMT）和目标本身的放射性的限制。该奖项将支持开发具有更简单的内部结构，更低的固有传感器放射性和比PMT更好的电荷分辨率的放射性纯混合光电传感器。加州大学戴维斯分校的团队还将设计和建造一个贵液测试单元，该单元将精确地调整探测器设计参数对荷光比背景抑制的影响。这项工作将与基于液氩的DarkSide-50 DM搜索计划中的相关分析相结合。采用荷光比抑制可以扩展DarkSide-50探测器在低质量DM搜索的重要能量区域的灵敏度。更广泛影响的主要焦点是为学生提供实践经验，从高中到研究生院，并就如何成功发展STEM职业提供指导。PI将与两个暑期学校计划协调这些努力：核分析技术（NAT）和加州数学和科学暑期学校（COSMOS）。该奖项还旨在提高代表性不足群体的学生在NAT学校的参与度，这些学生将通过加州大学戴维斯分校本科生（REU）物理学项目的研究经验的申请过程进行选择。

Multiple astronomical observations have established that about 85% of the matter in the universe is not made of known particles. Deciphering the nature of this so-called Dark Matter (DM) is of fundamental importance to cosmology, astrophysics, and high-energy particle physics. Our knowledge about DM existence has grown significantly over the past decade, mainly through observation of its gravitational influence. However, fundamental questions still remain unsolved: Is DM a particle? Is there more than one type of DM? Does it interact via non-gravitational force? We are systematically searching for DM and scrutinizing the claims of its detection, but to date, no one has reported a conclusive DM signal. This forces us to broaden our search, as well as to develop technologies capable of making measurements orders of magnitude more sensitive than what is currently available. Direct DM detection experiments aim to measure the energy deposited by DM as it scatters off the atoms in a detector. Among them, noble-liquid-based experiments are presently leading the field and are expected to improve the sensitivity of DM searches by two orders of magnitude by the end of this decade. To achieve this, the experiments rely heavily on increasing target mass and achieving a very low background environment. The current generation of noble-liquid DM detectors is limited by the radioactivity in the detector materials, the photomultipliers (PMTs), and the target itself. This award will support the development of radio-pure hybrid photosensors with a simpler internal structure, much lower intrinsic sensor radioactivity, and significantly better charge resolution than a PMT. The UC Davis team will also design and construct a noble liquid test cell that will precisely tailor the effects of detector design parameters on the charge-to-light ratio background rejection. This effort will be combined with a related analysis in the liquid-argon-based DarkSide-50 DM search program. Employing the charge-to-light ratio rejection can extend the sensitivity of the DarkSide-50 detector in the energy region of importance for low mass DM searches.The main focus of the broader impacts is hands-on experience for students, ranging from high school to graduate school, combined with providing mentorship on how to successfully develop a STEM career. The PI will coordinate these efforts with two summer school programs: Nuclear Analytical Techniques (NAT) and the California State Summer School for Mathematics and Science (COSMOS). This award also aims to increase participation in the NAT School of students of underrepresented groups who will be selected through the application process of the Research Experiences for Undergraduates (REU) Physics program at UC Davis.