Liquid Argon Detector R&D with Applications to the LEGEND and CCM Experiments

该奖项支持一项研究计划，该计划的重点是LEGEND实验，这是一项利用富集锗作为源和探测器的无中微子双β衰变实验。锗76同位素是少数几个已知经历极其罕见的双β衰变过程的原子核之一，产生两个电子和两个中微子。关于中微子的一个悬而未决的关键问题是，它是否是自身的反粒子。如果中微子是自身的反粒子，那么无中微子的衰变过程必然存在。这一过程的发现将对核物理学、基本粒子物理学和宇宙学领域产生革命性的影响。宇宙完全由没有反物质的物质组成，反物质的缺失可以用中微子本身就是反粒子来解释。这一研究项目将加强用液态氩探测电离辐射的技术，这对LEGEND本底抑制和其他核物理和粒子物理实验至关重要。这项工作非常适合培养未来的实验人员，更广泛地说，是STEM专业人员。新墨西哥大学阿尔伯克基分校是美国仅有的两所旗舰西班牙裔服务州立机构之一（美国教育部“高西班牙裔入学率”），也被卡内基基金会列为R1（博士大学-最高研究活动）。PI和联合PI积极从该校不同种族的本科生中招募新生，并在技术和科学技能方面对他们进行指导，使学生能够在STEM领域找到工作。LEGEND的主要挑战是去除和拒绝背景——LEGEND的目标是每年在信号区域中少于一个背景计数。实现这一目标的LEGEND策略的一部分是使用液态氩的闪烁光作为主动否决权。液态氩因其成本低、光产率好，在大型核物理和粒子物理实验中得到了广泛的应用。然而，由于氩闪烁光的波长较短（128 nm），液态氩实验需要使用波长移位器（通常是四苯基丁二烯，TPB，它在430 nm处重新发射光）来检测光。LEGEND目前的设计是在锗探测器阵列周围涂覆TPB闪烁光纤，以收集来自液态氩的光。在该小组先前的工作中，他们表明，添加少量的氙（~ 10ppm）可以将几乎所有的光转移到更有利的175 nm范围，将发射时间转移到更早的时间，并将产光率提高约两倍。该小组将在位于新墨西哥大学校园的小型（105升）低温容器的改进版本中进一步探索这一过程，并参与LEGEND-200的操作和数据分析以及未来LEGEND-1000的设计。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award supports a research program that focusses on the LEGEND experiment, a neutrino-less double beta decay experiment that utilizes enriched germanium as both source and detector. The germanium 76 isotope is one of a handful of nuclei known to undergo the exceedingly rare double-beta decay process, producing two electrons and two neutrinos. A crucial unanswered question regarding the neutrino is whether it is its own anti-particle. If the neutrino is its own anti-particle, then the neutrino-less decay process must exist. The discovery of this process would have a revolutionary impact on the fields of nuclear physics, elementary particle physics and cosmology. The universe consists entirely of matter without anti-matter, and the absence of anti-matter could be explained by a neutrino that is its own anti-particle. This research program will enhance the technique of detecting ionizing radiation with liquid argon, crucial for LEGEND background rejection and with applications to other nuclear and particle physics experiments. This work is ideal for educating future experimentalists and, more broadly, STEM professionals. The University of New Mexico-Albuquerque is one of only two Flagship Hispanic-Serving State Institutions in the US (US Department of Education "High Hispanic Enrollment") that is also classified by the Carnegie Foundation as R1 (Doctoral University-Highest research activity). The PI and co-PI actively recruit new students from the university’s ethnically diverse undergraduate pool and mentor them in technical and scientific skills that enable the students to pursue jobs in STEM fields.The major challenge of LEGEND is removal and rejection of backgrounds – the goal for LEGEND is less than one background count in the signal region per ton-year. Part of the LEGEND strategy for achieving this goal is to use scintillation light from liquid argon as an active veto. Liquid argon has become widely used in large nuclear and particle physics experiments because of its low cost and good light yield. However, due to the short wavelength of the argon scintillation light (128 nm) liquid argon experiments require the use of a wavelength shifter (typically Tetra-phenyl Butadiene, TPB, which re-emits the light at 430 nm) for the detection of the light. The current design of LEGEND has TPB coated scintillating fibers surrounding the germanium detector array to collect the light from the liquid argon. In the group‘s prior work they showed that the addition of a small quantity of xenon (~10 ppm) can shift nearly all the light to the more favorable 175 nm range, shift the emission to earlier times and increase the light yield by about a factor of two. The group will further explore this process in an improved version of a small (105 liter) cryogenic vessel located on campus at UNM, as well as participating in the operation and data analysis of LEGEND-200 and the design of the future LEGEND-1000.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.