Direct Dark Matter Search with LUC-ZEPLIN Experiment

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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.