Direct Dark Matter Search with LUC-ZEPLIN Experiment

LUX-ZEPLIN（LZ）实验是第二代暗物质直接探测实验，旨在通过核反冲相互作用探测弱相互作用大质量粒子（WIMP）。探测器的主要部件是一个双相氙TPC，其中含有7吨有效体积的液体氙。TPC由一层称为皮肤的液体氙以及含有钆负载液体闪烁体（GdLS）的外部探测器（OD）包围，它们一起充当否决系统以标记潜在的有问题的背景粒子，例如中子和伽马射线。理解和识别这些背景是寻找难以捉摸的暗物质信号的重要组成部分。OD的GdLS罐围绕着氙低温恒温器，本身被大型水箱包裹，作为屏蔽外部背景源的屏障。OD装有光电倍增管，光电倍增管位于水箱内，呈向内的圆柱形。为了有效地否决背景信号，OD对各种信号的响应必须很好地理解，并且在分析数据时必须使用适当的否决程序。使用光学校准系统（OCS）校准和监测外部检测器的响应，该光学校准系统由35个光注入点组成，该光注入点可以向检测器发射仔细控制的光脉冲，从而能够产生各种各样的信号。该项目包括在LZ的初始数据采集期之前和期间安装、测试和运行OCS。正在使用校准和WIMP搜索数据制定否决程序。这一程序将在2020年底前对第一批着陆区数据进行初步分析时实施，以了解和排除探测器中看到的背景信号。

The LUX-ZEPLIN (LZ) experiment is a second-generation dark matter direct-detection experiment which aims to detect Weakly Interacting Massive Particles (WIMPs) via nuclear recoil interactions. The main component of the detector is a dual-phase xenon TPC containing a 7-tonne active volume of liquid xenon. The TPC is surrounded by a layer of liquid xenon known as the Skin as well as an Outer Detector (OD) containing gadolinium-loaded liquid scintillator (GdLS), which together act as a veto system to tag potentially problematic background particles such as neutrons and gamma rays. Understanding and identifying these backgrounds is a vital part of the search for elusive dark matter signals.The OD's GdLS tanks surround the xenon cryostat and are themselves encased by the large water tank which acts as shielding against external background sources. The OD is instrumented with PMTs which are located in the water tank in an inward facing cylindrical formation. In order to effectively veto background signals, the response of the OD to various signals must be well understood and an appropriate veto procedure must be used when analysing the data. The response of the outer detector is calibrated and monitored using an Optical Calibration System (OCS) consisting of 35 light injection points which can emit carefully controlled pulses of light into the detector enabling a wide variety of signals to be produced. This project includes the installation, testing and operation of the OCS prior to and during LZ's initial data taking period.A veto procedure is being developed using calibration and WIMP search data. This procedure will be implemented in the initial analysis of the first LZ data, towards the end of 2020, in order to understand and exclude background signals seen in the detector.