The EXO search for Neutrino-less Double Beta Decay

这项申请寻求对EXO计划的支持，该计划正在寻找氙气中中微子较少的双β衰变。拟议的工作包括三项紧密结合的主要活动：现有的200公斤探测器EXO-200的工作；建立第一个探测倒置层次Nexo的探测器的工作；以及寻找达到正常层次的路线图的工作。*我们正在参与EXO-200探测器的运营和开发。这个开创性的探测器是第一个在数百公斤尺度上达到灵敏度的探测器，利用这个探测器，我们首次观测到了136Xe的两个中微子衰变。我们为无中微子衰变模式建立了一个极限，这在当时是一项世界纪录，这是第一次严重挑战海德堡-莫斯科合作小组对这一衰变过程的观测结果的测量。它已经决定再运行三年，以使双β衰变的敏感度提高约3倍。这将再次使探测器的灵敏度可与世界上最好的探测器相媲美。这项工作还为我们的学生和研究助理提供了物理主题。*工作的第二部分是为拟议的5吨探测器Nexo开发设计，合作计划在SNOLAB安装该探测器。如果获得批准，这将是这项关键物理研究中世界上最灵敏的探测器，并将覆盖中微子质量的整个倒置层次区域。虽然该探测器以EXO-200设计为基础，但仍有许多地方可以在设计上进行改进，或者200公斤探测器的设计不能很好地适应吨位标准。加拿大队在这一过程中非常积极。我们已经承担了光敏系统的主要责任，该系统将采用SIMS。另一个责任领域是校准交付系统的设计。这些活动是我们今后一段时期活动的主要部分。我们还开始探索是否可以找到成本更低的技术来浓缩氙气。具体地说，我们将开展研究，看看氙气同位素的蒸气压差是否足够大，以允许通过蒸馏分离。*最后，该小组正在展望未来，开发能够达到正常等级的探测器的概念。我们一直在探索的一种技术是在每一次事件中都加上一个子体钡离子的存在。我们已经为此制定了概念，并成功地测试了这一过程中的每个步骤，但现在我们必须将这些步骤结合起来，以研究一个完整的过程。了解流程的总体效率并衡量衡量的任何内在背景将是至关重要的。

This application seeks support for the EXO program searching for neutrino less double beta decay in xenon. The proposed work is comprised of three main, tightly coupled, activities: work on the existing 200 kg detector, EXO-200; work to establish the first detector to explore the inverted hierarchy, nEXO; and work to find a roadmap to reach the normal hierarchy.******We are participating in the operation and exploitation of the EXO-200 detector. This pioneering detector was the first to reach sensitivity at the hundred kilogram scale and with this detector we have made the first observation of the two neutrino decay of 136Xe. We established a limit for the neutrino less decay mode which at the time was a world record and it was the first measurement to seriously challenge the claimed observation of this decay process by the Heidelberg-Moscow collaboration. It has been decided to operate for another three years to get an improvement of about a factor of 3 in the sensitivity to double beta decay. This will again make the detector comparable in sensitivity to the best in the world. This work also provides physics topics for our students and research associates.******The second part of the work is the development of the design for the proposed 5 tonne detector nEXO, that the collaboration plan to install at SNOLAB. If approved this should be the world's most sensitive detector for this critical physics study and would provide coverage of the entire inverted hierarchy region of neutrino masses. While the detector has its basis in the EXO-200 design, there are a number of area where improvements can be made in the design or where the design of the 200 kg detector does not scale nicely to the tonne scale. The Canadian team has been very active in this process. We have undertaken major responsibilities for the light sensitive system which will employ SiMs. Another area of responsibility is the design of calibration delivery systems. These activities form a major part of our activities for the coming period. We have also started to explore if less expensive techniques can be found to enrich the xenon. Specifically, we will carry out studies to see if the vapour pressure differences of the xenon isotopes are large enough to permit separation by distillation.******Finally the group is looking ahead to develop concepts for detectors that can reach the normal hierarchy. One of the techniques we have been exploring is to tag each event with the presence of otherwise of a daughter barium ion. We have developed concepts for this and have been successfully testing each of the steps in the process but now we must combine the steps to study a complete process. It will be critical to understand the overall efficiency for the process and to measure any inherent backgrounds to the measurement.