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The Brown Particle Astrophysics group is focused on direct detection of dark matter. To this end the group performs R&D on low background, rare event search experiments. Currently the Particle Astrophysics group is an active member in the LUX and LZ dark matter search experiments. Both LUX and LZ are two-phase xenon Time Projection Chamber (TPC) detectors. The goal of LUX and LZ is to detect energy depositions caused by galactic dark matter particles known as WIMPs (Weakly Interacting Massive Particles) scattering off of atomic nuclei. Once LUX finishes its WIMP-search run, LZ will begin construction.
The site for LUX is the Davis Laboratory at the 4850 ft. level of the Sanford Underground Research Laboratory (SURF) at the Homestake Mine in Lead, SD. The detector is housed in an 8 m diameter (300 tonnes) water tank that acts as a background shield and muon veto. The LUX detector is comprised of 370kg of liquid xenon, 250kg of which define the active region observed by 122 Hamamatsu R8778 2-inch diameter photomultiplier tubes (61 in the top array, 61 in the bottom array). LZ will be in the same water tank, but will contain 7 tonnes of active liquid xenon and will have 488 Hamamatsu R11410 3-inch diameter PMTS.
The Particle Astrophysics group plays pivotal roles in all aspects of the experiment, with particular emphasis on Monte Carlo simulations, material radioactivity screening, PMT testing and deployment, digital electronics, data processing and data analysis. Monte Carlo simulations are performed using GEANT4 to study background and light collection of LUX. Future, larger scale detectors are also simulated.
The LUX Photomultiplier Tube program has been developed and implemented by the Brown Particle Astrophysics group. This includes testing the PMTs in liquid xenon, monitoring the health of the PMTs over time and performing gain calibrations using LEDs.
The data acquisition system (DAQ) in LUX was designed and implemented by the Particle Astrophysics group. The DAQ for LUX is unique in that it records only the interesting parts of the particle interaction. This prevents unwanted baseline from dominating the data stream and compromising the live time of the DAQ. This data is then analyzed and parameterized to distinguish WIMP candidate events from unwanted background.
The Particle Astrophysics group also hosts the primary data mirror for LUX data and plays a key role in developing and maintaining the data processing framework. By the end of LUX, the group will maitain nearly 1 petabyte of data, and more will be added for LZ. Additionally, Brown's Center for Computation and Visualization (CCV) is the primary processing center for all LUX data and contributes many millions of CPU-hours.
The LUX detector was assembled at the surface at Sanford Lab in 2010-2011, where it was successfully operated with all systems. It was then moved 4850 feet underground in 2012, and operated there starting October 2013. The first dark matter search results coming out of it were released publicly on October 30, 2013.
It will finish its WIMP-search run in the summer of 2016 before making way for the bigger, more sensitive LZ.