Extending the Sensitivity to the Detection of WIMP Dark Matter with an Improved Understanding of the Limiting Neutron Backgrounds
Extending the Sensitivity to the Detection of WIMP Dark Matter with an Improved Understanding of the Limiting Neutron Backgrounds
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通过更好地了解限制中子背景，扩展 WIMP 暗物质探测的灵敏度
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发表时间：
2005
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通讯作者：
S. Kamat
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作者：
S. Kamat
低温暗物质搜索 (CDMS) 使用位置敏感的锗和硅晶体直接探测弱相互作用大质量粒子 (WIMP)，据信构成了宇宙中大部分暗物质。 WIMP 与物质的相互作用很少见，识别和消除已知背景对于检测至关重要。探测器逐个事件的辨别拒绝了主要的伽马和贝塔背景，而蒙特卡罗模拟有助于估计和减去中子的贡献。本论文描述了理解中子背景的努力，如 CDMS 搜索 WIMP 的两个阶段所示。实验的第一阶段是在斯坦福地下设施的一个浅层地点进行的，那里的限制背景来自于洞穴周围岩石中宇宙射线μ介子相互作用产生的高能中子。该背景的模拟有助于对该站点的实验运行数据进行分析，并作为背景降低技术的输入，该技术是在 WIMP 核子截面上设置新的排除限制所必需的，排除质量为 8-20 GeV/c{sup 2} 的 WIMP 的新参数空间。本文考虑了所使用的模拟方法以及数据中的各种事件群体如何作为对模拟的检查，从而使它们能够用于解释 WIMP 搜索数据。研究还证实，浅层地点存在限制性中子本底，因此需要迁移至 713 米深的苏丹地下设施。类似的基于计算机的研究有助于量化在更深地点看到的中子背景，并为苏丹第一次物理实验中出现的数据分析提供信息。结合 WIMP 搜索和校准数据，模拟证实，增加的深度大大减少了所见的中子背景，从而大大提高了 WIMP 检测的灵敏度。对于 60 GeV/c{sup 2} 的 WIMP 质量，数据运行将 WIMP 核子截面的上限设置为 4 x 10{sup -43} 。背景中子速率的上限也已确定。« less
The Cryogenic Dark Matter Search (CDMS) uses position-sensitive Germanium and Silicon crystals in the direct detection of Weakly Interacting Massive Particles (WIMPs) believed to constitute most of the dark matter in the Universe. WIMP interactions with matter being rare, identifying and eliminating known backgrounds is critical for detection. Event-by-event discrimination by the detectors rejects the predominant gamma and beta backgrounds while Monte Carlo simulations help estimate, and subtract, the contribution from the neutrons. This thesis describes the effort to understand neutron backgrounds as seen in the two stages of the CDMS search for WIMPs. The first stage of the experiment was at a shallow site at the Stanford Underground Facility where the limiting background came from high-energy neutrons produced by cosmic-ray muon interactions in the rock surrounding the cavern. Simulations of this background helped inform the analysis of data from an experimental run at this site and served as input for the background reduction techniques necessary to set new exclusion limits on the WIMP-nucleon cross-section, excluding new parameter space for WIMPs of masses 8-20 GeV/c{sup 2}. This thesis considers the simulation methods used as well as how various event populations in the data served as checks on the simulations tomore » allow them to be used in the interpretation of the WIMP-search data. The studies also confirmed the presence of a limiting neutron background at the shallow site, necessitating the move to the 713-meter deep Soudan Underground Facility. Similar computer-based studies helped quantify the neutron background seen at the deeper site and informed the analysis of the data emerging from the first physics run of the experiment at Soudan. In conjunction with the WIMP-search and calibration data, the simulations confirmed that increased depth considerably reduced the neutron backgrounds seen, greatly improving the sensitivity to WIMP detection. The data run set an upper limit of 4 x 10{sup -43} on the WIMP-nucleon cross section for a WIMP mass of 60 GeV/c{sup 2} . Upper limits to the rate of background neutrons have also been determined.« less