XENON10 Collaboration: Construction and Operation of a Liquid Xe Dark Matter Detector

现在有确凿的证据表明，宇宙中约25%的质量能量密度是以“暗物质”的形式存在的。发现这种暗物质的本质是物理学和宇宙学中最重要的问题之一。也许最令人信服的想法是，暗物质是由被称为弱相互作用大质量粒子(Wimp)的亚原子粒子组成的，它们是在大爆炸中产生的。它们的质量很可能与金原子大致相同，但实际上小得令人难以置信，很难检测到。这类粒子是超对称性的一般预测，超对称性是迄今为止在加速器中探索的更高能量尺度上的粒子物理学的最佳激励理论。探测超对称性是欧洲核子研究中心大型强子对撞机的主要目标之一。如果WIMP确实存在，它们肯定也是我们银河系中的主要质量，并且应该可以从地球上探测器的相互作用中检测到。这些相互作用的速度可以从大爆炸中支配它们产生的相同物理机制中粗略地预测出来，不幸的是，它们的速度很小：大约在1个事件/公斤/月到1个事件/吨/年之间。粒子探测器中的环境背景，无论是来自放射性的还是来自宇宙射线的，都比这个大得多。目前的研究刚刚获得了对这些可能的最高速率的灵敏度。氙气合作开发了基于液体氙气的新一代暗物质探测器。与目前领先的探测器一样，这项技术能够区分大多数放射性背景(伽马射线和贝塔)和WIMP，前者导致探测器撞击后电子反冲，后者导致原子核反冲。然而，与目前质量约为1公斤的领先探测器相比，它有望更容易地扩展到完全检验WIMP假说所需的吨级规模。这里资助的工作是参与XENON10，这是一个大约10公斤的原型实验，将设在意大利Gran Sasso。我们的团队正在开发一种去除污染Xe的放射性Kr的系统，并正在开发一种新的方法来去除降低探测器性能的其他杂质。我们的团队还将参与探测器的设计和建造，特别是用于测量WIMP产生的电离的线栅，并致力于CSI系统的工作，以测量闪烁。暗物质的性质是物理学和宇宙学中最重要的问题之一，也是广大公众非常感兴趣的问题。我们的小组将积极参与公众宣传，特别是与当地学校的联系。本科生和研究生的教育和培训是这项工作的基础，学生将在拟议的研究中发挥主要作用。实验物理的技术方面为广泛的有益于公共利益的事业奠定了良好的基础。极低本底粒子探测的具体技术在核不扩散核查中也具有重要的国家安全作用。我们小组一直积极参与学术物理学家和国防防扩散界物理学家之间的联合努力，以开发先进的下一代低放射性本底筛选设施。这项工作将间接使这一努力受益。

The evidence is now overwhelming that ~ 25% of the mass-energy density of the universe is in the form of "dark matter". Discovering the nature of this dark matter is one of the most important questions in physics and cosmology. Perhaps the most compelling idea is that dark matter is composed of subatomic particles known as weakly interacting massive particles, or WIMPs, that were created in the big bang. They most likely have a mass roughly the same as an atom of gold, but are effectively incredibly small and difficult to detect. Such particles are a generic prediction of supersymmetry, the best-motivated theory for particle physics at higher energy scales than has been probed so far in accelerators. Probing for supersymmetry is one of the principle goals for the Large Hadron Collider at CERN. If WIMPs do exist, they must also be the dominant mass in our galaxy, and should be detectable from interactions in detectors on Earth. The rate of these interactions can be roughly predicted from the same physics that governs their production in the big bang, and is unfortunately small: somewhere between roughly 1 event/kg/month and 1 event/ton/year. Ambient backgrounds in particle detectors, both from radioactivity and cosmic rays, are much larger than this. Current searches have only just achieved sensitivity to the highest of these possible rates.The XENON collaboration has developed a new generation of dark matter detector based on liquid xenon. Like the current leading detectors, this technology has the ability to distinguish most radioactive backgrounds (gamma rays and betas), which cause an electron to recoil after the detector is struck, from WIMPs, which cause a nucleus to recoil. However it promises to more readily be scaled to the ton-scale needed to fully test the WIMP hypothesis than the current leading detectors, which have a mass of roughly 1 kg. The work funded here is participation in the XENON10, a ~10 kg prototype experiment which will be located in Gran Sasso, Italy. Our group is developing a system for removal of radioactive Kr which contaminates Xe, and is also developing a new method for removing other impurities that degrade the performance of the detector. Our group will also be involved in the design and construction of the detector, in particular wire grids used to measure ionization produced by WIMPs, and work on a CsI system for measuring scintillation. Finally, we will be involved in data taking operations and analysis.The nature of dark matter is one the most important questions in physics and cosmology, and is of great interest to the public at large. Our group will be actively engaged in public outreach, especially with local schools. Education and training of both undergraduate and graduate students is fundamental to this work, and students will have major roles in the proposed research. The technical aspects of experimental physics are a good foundation for a wide range of careers that benefit the public good. The specific techniques of very low background particle detection also have an important national security role in nuclear non-proliferation verification. Our group has been actively engaged in a joint effort between academic physicists and physicists in the defense non-proliferation community to develop advanced next-generation low radioactive background screening facilities. This work will indirectly benefit this effort.