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

Abstract

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.

Authors:
 [1]
  1. Massachusetts U., Amherst
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1497091
Report Number(s):
FERMILAB-THESIS-2018-26
1721688
DOE Contract Number:  
AC02-07CH11359
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Monte, Alissa Erin. Alpha Radiation Studies and Related Backgrounds in the DarkSide-50 Detector. United States: N. p., 2018. Web. doi:10.2172/1497091.
Monte, Alissa Erin. Alpha Radiation Studies and Related Backgrounds in the DarkSide-50 Detector. United States. doi:10.2172/1497091.
Monte, Alissa Erin. Mon . "Alpha Radiation Studies and Related Backgrounds in the DarkSide-50 Detector". United States. doi:10.2172/1497091. https://www.osti.gov/servlets/purl/1497091.
@article{osti_1497091,
title = {Alpha Radiation Studies and Related Backgrounds in the DarkSide-50 Detector},
author = {Monte, Alissa Erin},
abstractNote = {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.},
doi = {10.2172/1497091},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2018},
month = {1}
}

Thesis/Dissertation:
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