Session E16: Liquid Xenon Dark Matter III

VUV light reflectivity measurements from PTFE in Liquid Xenon for the LZ Dark Matter experiment

The LUX-Zeplin (LZ) collaboration is the next generation of the experiment to search for Dark Matter in the Universe with a dual-phase detector based on liquid xenon (LXe) with a target mass of 7 ton. LXe dual phase detectors are very sensitive probes to search for WIMP dark matter interactions. The LZ collaboration is conducting R{\&}D to study VUV light reflectivity from PTFE (Teflon) in LXe. Teflon is used in dual phase detectors both as an electrical insulator and as reflector of VUV scintillation light (\textasciitilde 175 nm) to improve photon detection with photomultiplier tubes (PMTs). However, experimental data for the reflectance of VUV light from PTFE in LXe is not sufficiently conclusive. We present a new technique of measuring the light reflectivity from PTFE by varying the fractional area of the PMT in the detector. PTFE reflectivity measurements were performed as a function of Teflon wall thickness in the range of 2 mm to 9.5 mm. The method, apparatus and experimental results will be presented.   

TPC GRID DESIGN IN LUX-ZEPLIN(LZ) AND LZ SYSTEM TEST

The lux-zeplin (lz) project is a dark matter direct detection experiment using liquid xenon in a large time projection chamber. The detection scheme requires an electric drift field and efficient light collection for the scintillation and charge signals, respectively. These requirements lead to design challenges for the thin wire grids and meshes that establish the fields with minimal impact on light collection and field non-uniformity. This talk will present the lz design, as informed by simulations and laboratory tests in the lz system test platform at slac.   

High Voltage Tests in the LUX-ZEPLIN System Test

The LUX-ZEPLIN (LZ) project is a dark matter direct detection experiment using liquid xenon. The detector is a time projection chamber (TPC) requiring the establishment of a large electric field inside of the detector in order to drift ionization electrons. Historically, many xenon TPC designs have been unable to reach their design fields due to light production and breakdown. The LZ System Test is scaled so that with a cathode voltage of -50 kV, it will have the fields that will be seen in the LZ detector at -100 kV. It will use a fully instrumented but scaled-down version of the LZ TPC design with a vessel set and gas system designed for quick turnaround, allowing for iterative modifications to the TPC prototype and instrumentation. This talk will present results from the high voltage tests performed during the first runs of the LZ System Test.   

Measurement of the Field-Dependent Response of Liquid Xenon to Low-Energy Electronic Recoils

The search for the direct detection of dark matter continues to be led by experiments employing liquid xenon (LXe) as the detection medium. Still, few measurements have been made of the response of LXe to low-energy interactions as a function of energy and electric field. The neriX detector at Columbia University is a dual-phase time projection chamber optimized for simultaneous measurements of light and charge from low-energy interactions in LXe. In this talk, we will present the results of measurements of the light and charge yield of electronic recoils in LXe using neriX. The Compton coincidence technique is employed to extract the yields as a function of energy deposited at different electric fields.   

Measurement of the Charge and Light Yield of Low Energy Nuclear Recoils in Liquid Xenon at Different Electric Fields

Dual-phase liquid xenon detectors continue to lead in the search for the direct detection of dark matter. Characterization of the response of liquid xenon to low energy ($\leq 20$ keV) nuclear recoils is essential to establish the sensitivity of these detectors to dark matter. The neriX detector at Columbia University is a dual-phase time projection chamber that is optimized for simultaneous measurements of light and charge from these low-energy interactions. A coincidence technique is employed to extract the light and charge yield from nuclear recoils in liquid xenon as a function of energy deposited and applied electric field. In this talk, we will present preliminary results from the light and charge yield measurements.   

Front-end electronics for the LZ experiment

LZ is a second generation direct dark matter detection experiment with 5.6 tonnes of liquid xenon active target, which will be instrumented as a two-phase time projection chamber (TPC). The peripheral xenon outside the active TPC (“skin”) will also be instrumented. In addition, there will be a liquid scintillator based outer veto surrounding the main cryostat. All of these systems will be read out using photomultiplier tubes. I will present the designs for front-end electronics for all these systems, which have been optimized for shaping times, gains, and low noise. Preliminary results from prototype boards will also be presented.   

DAX: A Versatile Testbed for Xenon Detector R{\&}D

The DAX (DAvis Xenon) system serves as a test bed for liquid-xenon (LXe) detector research and development, particularly in the context of future dark matter direct detection searches. A number of important technologies are being tested in this system, including an active liquid-purity monitor, silicon photomultiplier sensors, wavelength shifters, and a direct measurement of the scintillation and ionization response of LXe to low-energy Pb-206 recoils. The last item is important because Pb-206 is a decay product of Po-210, which is a prominent surface background resulting from radon plate-out, and its behavior in LXe is poorly understood. I discuss the motivation and design of this system, along with the current status and recent results of its goals.   

Design and First Results of the CoDeX Liquid-Xenon Compton-Imaging Detector

CoDeX (Compton-imaging Detector in Xenon) is an R&D Compton gamma-ray imaging detector that uses 30 kg of xenon in a two-phase time projection chamber. Time projection relative to the initial scintillation signal provides the vertical interaction positions, and either PMT-sensed gas electroluminescence or a charge-sensitive amplifier quantifies the drifted ionization signal. Detector features to enable Compton imaging are a pair of instrumented wire grids added to sense the horizontal position of clouds of drifted electrons that traverse the detector. Each wire is individually amplified in the cold xenon environment. Design choices addressing the thermodynamic and xenon purity constraints of this system will be discussed. We will also discuss the mechanical designs, engineering challenges, and performance of this Compton-imaging detector.