Background isolation techniques for future liquid xenon dark matter observatories

LUX-ZEPLIN是第二代暗物质实验，将于2020年在美国南达科他州铅市的桑福德地下研究设施投入使用。它将使用10吨液态氙和500个光电倍增管（PMT）来探测暗物质与常规物质相互作用的极其罕见的事件。为了明确探测难以捉摸的暗物质粒子，严格的数据分析程序至关重要，并得到探测器校准程序和相关模拟的支持。实验将使用一套内部分散的（83mKr, 131Xe， 220Rn和CH4标记的氚）和外部部署的密封中子（AmLi, 205, 206BiBe, 252Cf, 88YeBe）和伽马（57Co, 22Na, 133Ba, 228Th）辐射源，为背景事件和WIMP信号的响应提供高统计校准。罕见事件实验需要尖端的数据分析，支持极其精确的模拟调整现有和未来的校准数据，以及探测器响应模型。所有数据分析步骤和支持模拟和校准都必须非常健壮。一个非常重要的步骤是从脉冲序列中提取和识别单光子，这些脉冲序列是数字化仪从电子链中记录的，包括PMT、电缆、放大器板和进一步的电缆。这样做的算法已经存在，并且已经在适合现有实验的水平上进行了测试，但是，可以通过合并新技术和扩展模拟工具组合的能力来进一步改进。该项目的目标是开发特定的分析工具，并辅以详细的模拟，以提供对探测器对校准源响应的最佳理解。项目主要目标是通过改进光子探测算法、事件重建和触发能力，降低探测器的探测阈值，提高探测器的科学覆盖范围。除了使用LZ探测器的数据外，这还将涉及在氙时间投影室中生成特定事件的模拟（例如，重新使用校准事件），以前实验中记录的数据中的事件，并使用所有可用的信息，以提供和验证适当增强的算法。该项目的新颖性是通过关注迄今为止尚未被模拟和分析覆盖的探测器元素来确保的，这些元素要么完全没有覆盖，要么只是部分覆盖。该项目还有一个新的方面，与未来的光子传感设备有关，这一领域与牛津实验室的实验能力完美匹配。这将包括为未来的暗物质探测器开发低温电子设备和电缆解决方案。这项研究的一个关键新元素将是这些传感器的电子读出链的集成，这是建立在牛津大学之前开发的探测器电子响应模型的基础上的。该项目主要是基于计算机的，使用基于geant的仿真，ROOT数据分析包和LZAp分析框架。牛津大学是LZ协作组织的成员之一。硬件开发的一小部分将在牛津进行，主要是与伦敦帝国理工学院（Imperial College London）、布里斯托尔大学（Bristol）和利物浦大学（Liverpool）合作。

LUX-ZEPLIN is a generation-2 Dark Matter experiment being commissioned in 2020 at the Sanford Underground Research facility in Lead, South Dakota (USA). It will use 10 tonnes of liquid xenon and 500 photomultiplier tubes (PMT) to detect extremely rare events of dark matter interactions with regular matter. For the unambiguous detection of elusive dark matter particles rigorous data analysis procedures are vital, supported by a detector calibration programme and associated simulations. The experiment will use a suite of internally dispersed (83mKr, 131Xe, 220Rn and CH4 labelled tritium) and externally deployed sealed neutron (AmLi, 205, 206BiBe, 252Cf, 88YeBe) and gamma (57Co, 22Na, 133Ba, 228Th) radiation sources to provide high statistics calibration of the response to background events and WIMP signal. Rare-event experiments require cutting-edge data analysis, supported by extremely accurate simulations tuned existing and future calibration data, and a model of the detector response. All data analysis steps and supporting simulations and calibrations have to be extremely robust. A very important step is to extract and identify single photons from the pulse trains that the digitizers record from the electronics chain comprising PMT, cabling, amplifier board and further cabling. Algorithms to do this exist and have been tested at a level suitable for existing experiments, however, further improvements can be made by incorporating new techniques and expanding capabilities of the portfolio of simulation tools.The goal of this project is to develop specific analysis tools, supported by detailed simulations to provide an optimal understanding of the detector response to calibration sources. The main project objective is to enhance the science reach of the detector by lowering the detection threshold through improvements to the photon detection algorithms, event reconstruction and triggering capability. In addition to using data from the LZ detector, this will also involve generating simulations of particular events in a xenon time projection chamber (re-using calibration events, for example), events from data recorded in previous experiments and using all possible information that is available in order to provide and validate suitably enhanced algorithms. The novelty of the project is ensured by focussing on detector elements that so far have not been covered by simulation and analysis, either not at all or only partially. There is a further novel aspects to the project that is related to future photon sensing devices, an area that is ideally matched to the experimental capabilities of the Oxford laboratory. This will involve developing cryogenic electronics and cabling solutions for a future dark matter detector. A crucial novel element of this research will be the integration of the electronic readout chain for such sensors, building on previous work at Oxford that developed a detector electronics response model.The project is mostly computer based, using GEANT-based simulation, the ROOT data analysis package and the LZAp analysis framework. It is carried out within the LZ Collaboration of which Oxford is a member. The small element of hardware development will be carried out at Oxford, mainly, in collaboration with Imperial College London, Bristol and Liverpool.