Neutrino-Less Double Beta Decay with EXO-200 and EXO

这一奖项为该小组继续参与浓缩氙气天文台(EXO)计划提供了基础支持，该计划旨在寻找136-氙气中的无中微子双贝塔衰变，这是一个可能掌握中微子性质线索的核过程。对这种衰变的观察将意味着中微子是Majorana粒子，即它们自己的反粒子，对我们理解基本粒子的质量模式以及早期宇宙的结构和演化具有深远的影响。EXO-200实验是一个200公斤重的浓缩液体氙气探测器，目前正在新墨西哥州的废物分离试验厂(WIPP)的地下运行。该小组还将参与更灵敏的吨级EXO实验(Full-EXO)的开发和设计，以遵循EXO-200。随着计划在华盛顿大学进行的研究，该小组将为设计对中微子质量的灵敏度低至10 meV的全EXO实验提供关键投入，方法包括：i)优化探测器的光学响应和VUV探测效率，以及ii)提供单一的钡离子源，这可能是实现EXO特有的背景抑制方案的一种改变游戏规则的工具，该方案可寻找136-Xe双β衰变后Ba2+的出现。广泛影响：稀有液体探测器正在医疗成像设备以及核电站燃料成分的远程监测中找到应用。为EXO-200等探测器开发的超低本底方法已经将放射性污染带到了20年前被认为不可能实现的水平。电子工业感兴趣的工艺现在需要在它们的生产线上达到类似水平的放射性纯度。与EXO-200和EXO的合作为研究生提供了充分的机会进行尖端研究，并在中型国际科学合作中工作。

This award provides base support for the group to continue to participate in the Enriched Xenon Observatory (EXO) program to search for neutrino-less double beta decay in 136-Xenon, a nuclear process which could hold clues into the nature of neutrinos. Observation of this decay would imply that neutrinos are Majorana particles, i.e. their own antiparticles, with profound implications on our understanding of the pattern of masses of fundamental particles and of the structure and evolution of the early universe. The EXO-200 experiment, a 200-kg enriched liquid xenon detector is now running underground at the Waste Isolation Pilot Plant (WIPP) in New Mexico. This group will also take part in the development and design of a more sensitive tonne-scale EXO experiment (full-EXO) to follow EXO-200. With the planned research at UMass, the group will provide key input to the design of a full-EXO experiment with sensitivity to neutrino masses as small as 10 meV by: i) optimizing the optical response and VUV detection efficiency of the detector, and ii) supplying a single Barium ion source, a possibly game-changing tool for the realization of the EXO-specific background suppression scheme which looks for the appearance of Barium ions following 136-Xe double beta decay.Broader Impacts: Noble liquid detectors are finding applications in medical imaging devices as well as in remote monitoring of nuclear power plant fuel composition. The ultra-low background methods developed for detectors like EXO-200 have taken radioactive contamination to levels considered impossible to achieve just twenty years ago. Processes of interest for the electronics industry now require similar levels of radio-purity in their manufacturing lines. Work with EXO-200 and EXO provides ample opportunities for graduate students to perform cutting edge research and experience working in a medium-sized international scientific collaboration.