Direct Dark Matter Detection with the LUX-ZEPLIN Detector

Lux-ZEPLIN是一项第二代暗物质实验，将于2019/20年在美国南达科他州铅的桑福德地下研究设施部署并投入使用。它将使用10吨液体氙气和500个光电倍增管(PMT)来探测暗物质与普通物质相互作用的极其罕见的事件。对于被称为弱相互作用质量粒子(WIMP)的难以捉摸的暗物质粒子的明确探测，需要一个严格的探测器校准程序。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，228)辐射源，以提供对背景事件和WIMP信号响应的高统计校准。罕见事件实验需要精确的校准好的探测器，以及基于现有校准数据的极其精确的模拟，以模拟探测器的响应。除了校准之外，所有的数据分析步骤都必须非常稳健。一个非常重要的步骤是从数字化仪从包括PMT、布线、放大板和进一步布线的电子链记录的脉冲序列中提取和识别单个光子。这样做的算法已经存在，并已在适用于现有实验的水平上进行了测试，然而，通过结合新技术和对探测器响应细节的扩展理解，可以进行进一步的改进。本项目的目标是执行详细的模拟，以提供对探测器对校准源的响应的最佳理解。该项目的目标是模拟LZ实验中使用的中子源和伽马源的事件，并重建事件的位置和能谱，这是探测器校准的关键部分。改进光子探测、重建和触发工作将涉及生成氙气时间投影室中特定事件的模拟(例如，重新使用校准事件)、从先前实验中记录的数据生成事件以及使用所有可能的信息，以便提供和验证适当增强的算法。该项目的新颖性是通过将重点放在迄今没有被模拟和分析涵盖的探测器元件上来确保的，这些探测器元件要么根本没有覆盖，要么只是部分覆盖。该项目还有另一个新颖的方面，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。这将涉及为未来的暗物质探测器开发低温电子学和布线解决方案。这项研究的一个关键的新元素将是这类传感器的电子读出链的集成，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。该项目主要基于计算机，使用基于GEANT的模拟、Root数据分析包和LZAp分析框架。它是在LZ合作范围内进行的，牛津是该合作的成员。硬件开发的小部分将在牛津大学进行，主要是与伦敦帝国理工学院、布里斯托尔大学和利物浦大学合作。

LUX-ZEPLIN is a generation-2 Dark Matter experiment being deployed and commissioned in 2019/20 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 the elusive dark matter particle called Weakly Interacting Massive Particle (WIMP) a rigorous detector calibration programme is required. 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 exquisitely a well-calibrated detector as well as extremely accurate simulations tuned on existing calibration data, to model the detector response. In addition to the calibrations, all data analysis steps 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 the expanded understanding of detail of the detector response.The goal of this project is to perform detailed simulations to provide an optimal understanding of the detector response to calibration sources. The project objective is to simulate events from neutron and gamma sources used in the LZ experiment and reconstruct events' position and energy spectra, which is a key part of the detector calibration. Improving on photon detection, reconstruction and triggering effort will 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 a suitably enhanced algorithms. 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.