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AWB_PhDThesis_20140120.pdf (23.59 MB)

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LUX Thermosyphon Cryogenics and Radon-Related Backgrounds for the First WIMP Result

Bradley, Adam Wade
http://rave.ohiolink.edu/etdc/view?acc_num=case1390314556

Abstract Details

2014, Doctor of Philosophy, Case Western Reserve University, Physics.
The cold, non-baryonic dark matter hypothesis describes the motions of galaxies and clusters, as well as the character of the large scale structure of the universe. Particle freeze- out arguments suggest a weakly interacting massive particle (WIMP) plays the dark matter role. Decades of experiments have sought direct interaction with normal matter and this thesis describes the efforts of the Large Underground Xenon (LUX) experiment to directly detect WIMP-xenon recoils. The LUX detector is a 370-kg two-phase time projection chamber (TPC) deployed at the Davis Campus of the 4850’ Level of the Sanford Underground Research Facility. It col- lects scintillation and ionization signals from particle interactions in the liquid xenon (LXe) to measure deposited energy and recoil type. The xenon is purified by circulating through a heated zirconium getter, condensed and evaporated with heat exchangers, and calibrated with internal and external sources to characterize the detector response to gammas, betas, neutrons, and alphas in a keV-MeV energy range. Long, stable operation of the detector at 175 K is accomplished with the thermosyphon cryogenic system, which is a passive, gravity-assisted closed cooling loop. The phase change of a fixed amount of nitrogen transports heat from the detector to a thermal bath of liquid nitrogen (LN) above the cryostat. It delivers 1000 W of cooling power through four loops whose transport tubing fits within a 6-inch diameter tube to cool the cryostat in a water tank 6.5 m below the LN bath. Low-power heaters provide temperature control to within 0.1 K. This system provided months of stable operation underground at 25-slpm xenon circulation with a 5-W heat load. The first WIMP hunt consisted of 85 live-days of data acquisition. Alpha decays from radon were observed and studied to characterize their background contributions to the WIMP analysis. The (a,n) rate and electron recoils from beta decays in the 222Rn chain were found to be sub-dominant to other irreducible backgrounds. All backgrounds were carefully measured to create a model used in the profile likelihood ratio test statistic for the first LUX result that produced the most sensitive WIMP limit to date.
Tom Shutt, PhD (Advisor)
Dan Akerib, PhD (Advisor)
John Ruhl, PhD (Committee Member)
Harsh Mathur, PhD (Committee Member)
Stacy McGaugh, PhD (Committee Member)
233 p.
Astrophysics; Particle Physics; Physics
dark matter; particle astrophysics; radon; thermosyphon; WIMP; LUX; Homestake; SURF;

Recommended Citations

Citations

  • Bradley, A. W. (2014). LUX Thermosyphon Cryogenics and Radon-Related Backgrounds for the First WIMP Result [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1390314556

    APA Style (7th edition)

  • Bradley, Adam. LUX Thermosyphon Cryogenics and Radon-Related Backgrounds for the First WIMP Result. 2014. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1390314556.

    MLA Style (8th edition)

  • Bradley, Adam. "LUX Thermosyphon Cryogenics and Radon-Related Backgrounds for the First WIMP Result." Doctoral dissertation, Case Western Reserve University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1390314556

    Chicago Manual of Style (17th edition)

case1390314556
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© 2013, some rights reserved.Creative Commons License LUX Thermosyphon Cryogenics and Radon-Related Backgrounds for the First WIMP Result by Adam Wade Bradley is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.