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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2018)

CUORE---the Cryogenic Underground Observatory for Rare Events---is an experiment searching for the neutrinoless double-beta ($0\nu\beta\beta$) decay of $^{130}$Te, based at the Laboratori Nazionali del Gran Sasso in Italy. The detector consists of 988 5$\times$5$\times$5 cm$^3$ TeO$_2$ crystals operated as bolometers at temperatures of $\sim$10 mK inside the world's largest and most powerful dilution refrigerator. CUORE began physics data collection in the spring of 2017, and has recently released its first limit on the $0\nu\beta\beta$ decay half-life of $^{130}$Te from 24 kg $\cdot$ y isotope exposure ($\sim$2 months live time). This result---T$^{0\nu}_{1/2} > 1.5 \cdot 10^{25}$ y (Bayesian) and T$^{0\nu}_{1/2} > 2.3 \cdot 10^{25}$ y (Frequentist) at $90 \%$ C.L.---is the most stringent to date and, together with two alternative analyses necessary to calculate it, forms the centerpiece of this thesis. In the future, with five years of live time, CUORE is projected to reach a median sensitivity of $9 \cdot 10^{25}$ y on this half-life. Besides the main physics conclusions, in this work I present an analysis modeling the spectral line shape of the bolometer, which is used for constructing the region of interest fit PDF. Additionally, I discuss the major CUORE hardware projects to which I have contributed in a significant way. Specifically, these are our world-leading cryostat, a cryogenic feedback temperature control system, a radon-free detector installation environment, and a room temperature detector calibration system.

    Cover page: Searching for the 0νββ Decay of 130Te with the Ton-Scale CUORE Bolometer Array
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2017)
    The design of low temperature bolometric detectors for rare event searches necessitates careful selection and characterization of structural materials based on their thermal properties. We measure the thermal conductivities of polytetrafluoroethylene (PTFE) and Al2O3 ceramic (alumina) in the temperature ranges of 0.17–0.43 K and 0.1–1.3 K, respectively. For the former, we observe a quadratic temperature dependence across the entire measured range. For the latter, we see a cubic dependence on temperature above 0.3 K, with a linear contribution below that temperature. This paper presents our measurement techniques, results, and theoretical discussions.
      Cover page: Thermal conductivity measurements of PTFE and Al2O3 ceramic at sub-Kelvin temperatures
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2019)
      The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for neutrinoless double beta decay that has been able to reach the 1-ton scale. The detector consists of an array of 988 TeO 2 crystals arranged in a cylindrical compact structure of 19 towers, each of them made of 52 crystals. The construction of the experiment was completed in August 2016 and the data taking started in spring 2017 after a period of commissioning and tests. In this work we present the neutrinoless double beta decay results of CUORE from examining a total TeO 2 exposure of 86.3 kg yr, characterized by an effective energy resolution of 7.7 keV FWHM and a background in the region of interest of 0.014 counts/(keV kg yr). In this physics run, CUORE placed a lower limit on the decay half-life of neutrinoless double beta decay of 130 Te ≤ 1.3 · 10 25 yr (90% C.L.). Moreover, an analysis of the background of the experiment is presented as well as the measurement of the 130 Te 2vββ decay with a resulting half-life of T 2v1/2 = [7.9 ± 0.1 (stat.) ± 0.2 (syst.)] x 10 20 yr which is the most precise measurement of the half-life and compatible with previous results.
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