Collaborative Research for Underground Science: Barium Tagging for EXO

对无中微子双β衰变的观测将有助于确定中微子的质量，发现轻子数违反，并揭示自然界中是否存在双组分马约拉纳费米子。EXO是一个多吨的中微子双β衰变实验，使用氙-136同位素富集到80%的氙，现在正在新墨西哥州的WIPP地下站点采集数据。然而，下一代这样的实验需要先进的背景还原方法来达到低于0.01 eV的马约拉纳中微子质量灵敏度。EXO正在开发一种新技术，利用原子光谱学来标记在无中微子双β衰变最终状态下产生的钡（Ba）。这项技术有望大幅减少放射性背景，提供一个干净、明确的测量，具有前所未有的灵敏度。最近在ba标签方面取得了突破。这些团队首次实现了超过1%的运输和标签效率。该奖项资助的研发工作建立在这些突破的基础上，并渴望首次展示在液态氙中高效标记单个Ba原子。更广泛的影响：虽然该提案的主要科学目标是在中微子物理领域，但其更广泛的影响是实质性的。正在开发的技术涵盖了一系列主题，从核和粒子天体物理学到AMO、表面物理学和材料科学。这项研究如果成功，可能适用于其他科学和技术问题，其中对单原子的高效转移和识别将感兴趣。例子包括国土安全应用的痕迹分析和罕见现象的检测。该团队还计划继续暑期项目，将高中教师纳入他们的实验室。

The observation of neutrinoless double beta decay will help determine the masses of neutrinos, discover lepton number violation and reveal if two-component Majorana fermions exist in Nature. EXO, a multi-tonne neutrinoless double beta decay experiment employing xenon enriched to ~80% in the isotope Xenon-136, is now taking data at the WIPP underground site in New Mexico. However, the next generation of such experiments requires advanced background reduction methods to reach Majorana neutrino mass sensitivities below 0.01 eV.EXO is developing a novel technique to tag the Barium (Ba) produced in the final state of the neutrinoless double beta decay using atomic spectroscopy. This technique has the promise of drastically reducing radioactive backgrounds, providing a clean and un-ambiguous measurement with unprecedented sensitivity. Recent breakthroughs have been obtained in the Ba-tagging front. These groups have produced, for the first time, Ba transport and tagging efficiencies above 1%. The R&D work funded with this award builds on such breakthroughs and aspires to provide the first demonstration of high efficiency tagging of individual Ba atoms in liquid xenon. Broader impacts: While the primary scientific goal of this proposal is in the field of neutrino physics, its broader impact is substantial. The techniques being developed span a range of topics, from nuclear and particle astrophysics, to AMO, surface physics and material science. This research, if successful, is likely to be applicable to other problems in science and technology, where the high efficiency transfer and identification of single atoms would be of interest. Examples include trace analysis for homeland security applications and the detection of rare phenomena. The team is also planning to continue the summer program integrating high school teachers into their labs.