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A Study of the Potential for Gamma Rays to Mimic WIMP Signals in DEAP-3600

  • Author / Creator
    Bina, Catherine E.
  • Identification of, and discrimination against, background radiation is of the utmost importance in dark matter searches. DEAP-3600 (Dark Matter Experiment using Argon Pulse shape discrimination) is a single phase, direct dark matter detector with a 3300 kg liquid argon target housed in a spherical acrylic vessel viewed by 255 photomultiplier tubes (PMTs). It is used to search for spin independent interactions of Weakly Interacting Massive Particle (WIMP) dark matter with the liquid argon nuclei. The measured energy resolution represents the detector’s ability to distinguish between sources of ionizing radiation. This is determined to be 3.92±0.09% in data for the 2.6 MeV gamma line from 208Tl after correcting for the relative efficiencies and channel gain of the PMTs. The simulated energy resolution for the same gamma line is found to be 2.59±0.02% when the PMTs do not produce afterpulsing and 2.86±0.02% with the creation of afterpulses. The difference between data and simulation is briefly discussed.Some of the largest sources of backgrounds in direct dark matter detectors stem from the detector components themselves. This is the case for gamma radiation within DEAP- 3600, which is produced primarily by uranium and thorium in the glass of the PMTs. An investigation of false WIMP signals produced by high-energy gamma rays stemming from the PMTs has been conducted with the use of Monte Carlo simulations and is presented in this work. The mechanism by which they are most likely to produce WIMP signals is presented. A comparison of the simulated events in the region of interest (ROI) with events from data is performed. The effect of afterpulsing on an event’s probability to be in the ROI is also studied.

  • Subjects / Keywords
  • Graduation date
    Spring 2019
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-yb3q-cv36
  • License
    Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.