Alpha Radiation Studies and Related Backgrounds in the DarkSide-50 Detector

Thesis/Dissertation · Mon Jan 01 04:00:00 EST 2018

DOI:https://doi.org/10.2172/1497091· OSTI ID:1497091

Monte, Alissa Erin ^[1]

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1. Massachusetts U., Amherst

DarkSide-50 is the current phase of the DarkSide direct dark matter search pro- gram, operating underground at the Laboratori Nazionali del Gran Sasso in Italy. The detector is a dual-phase argon Time Projection Chamber (TPC), designed for direct detection of Weakly Interacting Massive Particles (WIMPs), and housed within a veto system of liquid scintillator and water Cherenkov detectors. Since switching to a target of low radioactivity argon extracted from underground sources in April 2015, the background is no longer dominated by naturally occurring $$^{39}$$Ar. However, alpha backgrounds from radon and its daughters remain, both from the liquid argon bulk and internal detector surfaces. In some cases, the alpha events are a dangerous background in need of mitigation. In others, the alpha events can be used as a tool to deepen our understanding of our detector. We present here several analyses of alpha events in DarkSide-50. An analysis of radon-polonium coincidences is perfo rmed, yielding measurements of ion mobility and charged daughter fraction in liquid argon. These coincidences are also used to place upper limits on XY-resolution and liquid argon motion in the detector. A method for simulating the degraded energy spectra from $$^{210}$$Po events traveling through surface materials is presented and compared with data from DarkSide-50. Lastly, a pileup background created by the accidental coincidence of scintillation-only $$^{210}$$Po surface events with random ionization-like pulses is thoroughly discussed. The estimation of this background and its mitigation informed the recent WIMP search analysis performed with 532 live-days of DarkSide-50 data.

• Research Organization: Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
• DOE Contract Number: AC02-07CH11359
• OSTI ID: 1497091
• Report Number(s): FERMILAB-THESIS-2018-26; 1721688
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS