Pulse Shape Discrimination Studies In Liquid Argon For The Deap 1 Detector

Author : Benjamin R. Schlitzer
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.6/5 (912 download)

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Download or read book Characterization of Liquid Argon Response for the Direct Detection of Dark Matter written by Benjamin R. Schlitzer and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The nature of dark matter remains one of the most significant open questions in modern physics, despite the large body of astrophysical and cosmological evidence supporting its existence. The Weakly Interacting Massive Particle (WIMP) is a well-motivated candidate particle with mass in the range 1 GeV/c2 - 100 TeV/c2 and coupling to Standard Model matter at or below the weak scale. If WIMPs do exist, they should occasionally interact with baryonic particles and leave behind a small amount of energy. DarkSide is a phased experimental program which aims to detect the interaction of a WIMP with a liquid argon target in a dual-phase time projection chamber (TPC). In order to make a WIMP discovery, an accurate understanding of the signal region is required. To this end, small-scale experiments which measure the detector response to a recoiling argon nucleus (NR) or scattering with atomic electrons (ER) are critical in establishing results of the large-scale direct detection experiments. The Argon Response to Ionization and Scintillation (ARIS) experiment was designed to characterize liquid argon's response to both NR and ER events at low recoil energies using a small dual-phase TPC. This work presents a complete chronology of the ARIS experiment and analysis of the collected data. A detailed description of the design of the ARIS TPC and related subsystems is given, as well as an account of the commissioning and calibration performed at the University of California, Los Angeles. The inverse-kinematics neutron source LICORNE was used at the Institute De Physique Nucléaire Orsay to bombard the ARIS TPC with collimated low energy neutrons. Neutron detectors surrounding the TPC were used to tag events which scattered in the TPC at selected angles, and the resulting data were used to characterize both NR and ER events at tightly constrained recoil energies. A description of the low-level reconstruction and data selection cuts is given, as well as corrections made due to trigger efficiency and vertical position in the TPC. ER data were analyzed to provide an improved measurement of the linearity of LAr light yield for incident [gamma]/[beta] particles with energies below 511 keV. ARIS measured a constant light yield to within 1.6% in the [41.5, 511] keV recoil energy range. The linearity of the ER scintillation response measured by ARIS has also been used to derive the spectral shape of forbidden 39Ar [beta] decay, which is a background intrinsic to liquid argon. The NR data were analyzed to measure the relative scintillation efficiency for recoils between [7.1, 117.8] keV, and were in good agreement with the previous SCENE results at low recoil energy. The DarkSide collaboration has used ARIS results to precisely model the response of nuclear recoils in liquid argon in both field-on and field-off configurations. In addition to the characterization of argon response, this work presents an optimization of the electric fields used to drift ionization electrons in DarkSide TPCs. The relevant electrostatics models used by COMSOL simulation software to approximate electric field behavior are described, as well as a technique developed to quantify field uniformity in the TPC. Then, the uniformity of the electric field is optimized for several possible TPC design changes, including the fiducial radius, the first shaping ring voltage, and the cross-sectional geometry of shaping rings. This work was supervised by Dr. Emilija Pantic, and was completed in collaboration with both members of the DarkSide collaboration as well as scientists at the University of California, Davis.