Optical Calibration System of the LUX-ZEPLIN Outer Detector

The LUX-ZEPLIN (LZ) dark matter experiment utilizes a dual-phase xenon time projection chamber (TPC) with 7 tonnes of liquid xenon, primarily searching for nuclear recoils induced by interactions of Weakly Interacting Massive Particles (WIMPs) with xenon nuclei. Surrounding the TPC enclosed in a double-walled cryostat is an Outer Detector (OD) veto system, consisting of approximately 17 tonnes of gadolinium-loaded liquid scintillator housed in acrylic tanks, and 238 tonnes of ultra-pure water forming the outermost layer. The OD's primary function is to veto neutron single-scatter events in the liquid xenon TPC by detecting neutron scattering or gammas from neutron capture in the OD. The OD is equipped with 120 Hamamatsu R5912 photomultiplier tubes (PMTs), organized in arrays to monitor its volume. An Optical Calibration System (OCS), integrated within OD PMT arrays, facilitates the calibration and monitoring of these PMTs. This presentation will provide an overview of the OD and the OCS. The results of the detector monitoring via the OCS will also be presented.