A Midscale U.S. Proposal for the LEGEND 200 Experiment

中微子是宇宙中最多产的粒子，它们在理解为什么宇宙中的物质比反物质多方面起着重要作用。 中微子的质量非常小，电荷为零，因此它们可能是自己的反粒子。如果是这样的话，这就可以解释为什么物质比反物质多。唯一可行的实验方法来回答这个问题是寻找无中微子双β衰变（NLDBD），一种非常罕见的核衰变形式。该奖项将支持一个项目，该项目增加并汇集了最好的美国（Majorana Demonstrator）和欧洲（GERDA）实验，使用锗寻找无中微子双β衰变到一个名为LEGEND-200的新实验中。 该实验将使用200公斤由浓缩锗制成的特殊探测器，并将在意大利的Gran Sasso国家实验室进行。 可能受益于作为实验一部分开发的新技术的领域包括：环境监测;大气、海洋和地下水环境迁移;放射性年代测定方法;反应堆监测;确定极低职业辐射照射的生物测定;以及涉及极低放射性示踪剂的生物研究。 学生和博士后将接受地下科学相关学科的培训，如低背景技术，探测器技术，核物理和中微子物理。当前一代Ge-76实验，GERDA和马约拉纳演示器（MJD），利用高纯度锗探测器的固有能量分辨率为0.12%，已经实现了最低的背景超过一个数量级的NLDBD信号区域相比，其他NLDBD实验。 在这一成功的基础上，LEGEND合作正在开发下一代NLDBD实验，其半衰期为1028年，具有发现潜力。 该奖项为美国参与建设和调试几乎下一代NLDBD实验提供了中等规模的支持，该实验使用了高达200公斤的Ge-76二极管，即LEGEND-200（L-200），有可能提供物理学，并作为未来吨级实验的先驱。 L-200基于结合MJD开发的技术来生产超净组件和GERDA的背景抑制，以屏蔽液氩浴中的探测器，此外还将现有的MJD和GERDA探测器，资源和基础设施与新探测器进行物理结合。 L-200将位于意大利的Gran Sasso国家实验室，并将探测器部署在现有的GERDA低温恒温器中。 L-200将具有世界领先的发现潜力，1吨 * 年暴露的半衰期灵敏度为10^27年。该奖项反映了NSF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。

Neutrinos are the most prolific particle in the Universe and they have an important role in understanding why the Universe has more matter than anti-matter. Neutrinos have very small mass and zero electric charge so they could be their own anti-particle. If that is the case, this might explain why there is more matter than anti-matter. The only experimentally feasible way to answer this question is to look for neutrinoless double beta decay (NLDBD), a very rare form of nuclear decay. This award will support a project that adds to and brings together the best U.S. (Majorana Demonstrator) and European (GERDA) experiments using germanium to look for neutrinoless double beta decay into a new experiment called LEGEND-200. The experiment will use 200 kg of special detectors made out of enriched germanium and will take place at the Laboratori Nazionali del Gran Sasso in Italy. Among the fields that may benefit from the new technology developed as part of the experiment are: environmental monitoring; atmospheric, ocean, and groundwater environmental transport; methods of radioactive dating; reactor monitoring; bioassay for determining very low occupational exposures to radiation; and biological studies involving radiotracers at very low activities. Students and postdocs will be trained in underground science related disciplines, such as low-background techniques, detector technology, nuclear physics and neutrino physics. The current generation Ge-76 experiments, GERDA and the Majorana Demonstrator (MJD), utilizing high purity Germanium detectors with an intrinsic energy resolution of 0.12%, have achieved the lowest backgrounds by over an order of magnitude in the NLDBD signal region compared to other NLDBD experiments. Building on this success, the LEGEND Collaboration is developing a next-generation NLDBD experiment with discovery potential at a half-life of 1028 years. This award provides mid-scale support for U.S. involvement in building and commissioning an almost-next-generation NLDBD experiment using up to 200 kg of Ge-76 diodes ie LEGEND-200 (L-200) that has potential to deliver physics and serve as a forerunner to a future ton-scale experiment. L-200 is based on combining the techniques developed by MJD to produce ultra-clean components and GERDA's background suppression from shielding the detectors in a liquid argon bath, in addition to physically combining the existing MJD and GERDA detectors, resources and infrastructure with new detectors. L-200 will be based at the Laboratori Nazionali del Gran Sasso in Italy, and deploy the detectors in the existing GERDA cryostat. L-200 would have world leading discovery potential and a half-life sensitivity of 10^27 yr for a 1 t*yr exposure.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.