The Search for 0νββ Decay in 130Te with CUORE-0 by Jonathan Loren Ouellet Ph.D. Thesis Department of Physics University of California, Berkeley Berkeley, Ca 94720 and Nuclear Science Division Ernest Orlando Lawrence National Laboratory Berkeley, Ca 94720 Spring 2015 This material is based upon work supported by the US Department of Energy (DOE) Office of Science under Contract No. DE-AC02-05CH11231 and by the National Science Foundation under Grant Nos. NSF-PHY-0902171 and NSF-PHY-1314881. DISCLAIMER This document was prepared as an account of work sponsored by the United States Gov- ernment. 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The Search for 0νββ Decay in 130Te with CUORE-0 by Jonathan Loren Ouellet A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Physics in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Yury Kolomensky, Chair Professor Gabriel Orebi Gann Professor Eric B. Norman Spring 2015 The Search for 0νββ Decay in 130Te with CUORE-0 Copyright 2015 by Jonathan Loren Ouellet 1 Abstract The Search for 0νββ Decay in 130Te with CUORE-0 by Jonathan Loren Ouellet Doctor of Philosophy in Physics University of California, Berkeley Professor Yury Kolomensky, Chair This thesis describes the design, operation and results of an experimental search for neutri- noless double beta decay (0νββ) of 130Te using the CUORE-0 detector. The discovery of 0νββ would have profound implications for particle physics and our un- derstanding of the Universe. Its discovery would demonstrate the violation of lepton number and imply that neutrinos are Majorana fermions and therefore their own anti-particles. Com- bined with other experimental results, the discovery of 0νββ could also have implications for understanding the absolute neutrino mass scale as well as the presently unknown neutrino mass hierarchy. The CUORE experiment is a ton-scale search for 0νββ in 130Te expected to begin oper- ation in late 2015. The first stage of this experiment is a smaller 39-kg active-mass detector called CUORE-0. This detector contains 11 kg of 130Te and operates in the Laboratori Nazionali del Gran Sasso lab in Italy from 2013 { 2015. nat The results presented here are based on a TeO2 exposure of 35.2 kg·yr, or 9.8 kg·yr exposure of 130Te collected between 2013 { 2015. We see no evidence of 0νββ and place an −24 −1 upper limit on the 0νββ decay rate of Γ0νββ < 0:25 × 10 yr (90% C.L.), corresponding 0ν 24 to a lower limit on the half-life of T1=2 > 2:8 × 10 yr (90% C.L.). We combine the present result with the results of previous searches in 130Te. Combining it with the 1.2 kg·yr 130Te exposure from the Three Towers Test run we place a half-life limit 0ν 24 130 of T1=2 > 3:3 × 10 yr (90% C.L.). And combining these results with the 19.75 kg·yr Te exposure from Cuoricino, we place the strongest limit on the 0νββ half-life of 130Te to date, 0ν 24 at T1=2 > 4:5 × 10 yr (90% C.L.). Using the present nuclear matrix element calculations for 130Te, this result corresponds to a 90% upper limit range on the effective Majorana mass of mββ < 250 − 710 meV. i To my family ii Contents Contents ii List of Figures iv List of Tables vi 1 Introduction 1 1.1 Baryon Asymmetry and the Sakharov Conditions . 2 1.2 Neutrinos and Neutrino Mass . 4 1.3 Neutrinoless Double Beta Decay . 8 2 Double Beta Decay 9 2.1 Neutrinos in the Standard Model . 9 2.2 2νββ and 0νββ .................................. 15 2.3 Phase Space and Nuclear Matrix Elements . 21 2.4 Alternate 0νββ Models . 24 2.5 Experimental Sensitivity . 27 2.6 Present Experimental Searches for 0νββ .................... 28 3 The CUORE and CUORE-0 Experiments 31 3.1 A Bolometric Detector . 32 3.2 Predecessor To CUORE: Cuoricino . 38 3.3 CUORE Construction and Assembly Line . 42 3.4 The CUORE Cryostat . 45 3.5 The CUORE-0 Experiment . 46 4 CUORE-0 Data Collection and Processing 49 4.1 CUORE-0 Detector Setup and Data Taking . 49 4.2 First-Level Data Processing . 55 4.3 CUORE-0 Second-Level Data Processing . 67 5 CUORE-0 Noise Analysis And Decorrelation 81 5.1 The Full Noise Covariance Matrix and Subsets . 81 iii 5.2 Correlated Noise and Crosstalk . 85 5.3 Low-Frequency Correlated Noise In CUORE-0 . 88 5.4 Towards A Decorrelating Filter . 95 5.5 The Decorrelation Procedure in the Diana v02.30 Production . 98 5.6 Decorrelating Filter Performance . 101 6 CUORE-0 Analysis and 0νββ Fit 107 6.1 Final Physics Spectra . 108 6.2 Efficiency Evaluation . 111 6.3 208Tl Line Shape From Calibration . 112 6.4 Projecting the Detector Response . 120 6.5 0νββ ROI Fit Technique . 124 6.6 Systematics Accounting . 131 6.7 Final CUORE-0 0νββ Limit . 135 6.8 Differences with Official CUORE-0 Result . 136 7 CUORE and Beyond 140 7.1 Outlook for CUORE . 140 7.2 Beyond CUORE . 142 Bibliography 145 A CUORE-0 Dataset Data 155 B Generalized Amplitude Evaluation 165 B.1 Derivation of the Generalized Optimum Filter . 165 B.2 Special Cases . 170 B.3 Waveform Filtering in CUORE-0 . 174 C Bayesian Nuisance Parameters 176 D The Coldest Cubic Meter in the Universe 179 D.1 Low Temperature Regions in Nature . 179 D.2 The CUORE Cryostat . 180 D.3 Discussion . 181 D.4 Caveats, Qualifications, Ifs and Buts.. 182 D.5 More on the CMB . 183 iv List of Figures 1.1 Baryon number-violating processes . 3 1.2 Predicted solar neutrino spectrum . 5 1.3 Measuredν ¯e survival probability in KamLAND . 6 1.4 Fermion mass scales . 7 2.1 Possible Neutrino Hierarchies . 12 2.2 The A = 130 isobar . 17 2.3 Schematic of a 2νββ and 0νββ spectrum . 18 2.4 Majorana mass generation via the butterfly diagram . 19 2.5 Double beta decay Feynman diagrams . 20 2.6 Sum over intermediate states in a ββ decay . 23 2.7 Q-values and nuclear figures of merit . 24 2.8 Non-Standard 0νββ Mechanisms . 26 2.9 Plot of mββ vs mLightest ................................ 29 3.1 Schematic of LNGS lab . 32 3.2 Spectra for 2νββ and 0νββ ............................. 33 3.3 Idealized bolometer model . 34 3.4 NTD resistance curve . 36 3.5 CUORE NTDs . 36 3.6 CUORE bolometers and tower assembly . 38 3.7 Drawing of the CUORE detector . 39 3.8 Schematic NTD bias circuit . 39 3.9 Schematic of the bolometer readout chain . 40 3.10 The Cuoricino tower and result . 41 3.11 Energy spectrum from CCVR8 . 42 3.12 CUORE Assembly Line . 45 3.13 Drawing of the CUORE cryostat . 46 3.14 The CUORE-0 cryostat . 48 4.1 Pulser amplitude as a function of bias . 50 4.2 CUORE-0 event pulses . 51 v 4.3 Example of bad interval . 56 4.4 Average pulse and noise for channel 18 on dataset 2073 . 58 4.5 Baseline trends for stabilization algorithm . 60 4.6 Calibration of channel 18 in dataset 2070 . 63 4.7 Distribution of residual coincidence jitter . 66 4.8 Spatial correlations in coincidence . 67 4.9 Schematic of data salting . 68 4.10 Shifting channel calibrations . 70 4.11 Comparison of old and new optimum filters . 72 4.12 A channel recovered with WoH Stabilization . 73 4.13 Selection of shifted and unshifted channels . 75 4.14 Comparing the performance of two energy estimators . 76 4.15 Optimized distribution of energy estimators . 77 4.16 Comparison of possible FWHM distributions . 78 4.17 Robustness of the aggressive approach . 79 5.1 The full correlation matrix . 83 5.2 Frequency-frequency covariance matrices . 84 5.3 High frequency spikes in the NPS . 86 5.4 Channel-channel covariance matrix between 6-8 Hz . 87 5.5 Effect of channel crosstalk . 88 5.6 20 s sampled pulses . 89 5.7 Low-frequency ANPS . 89 5.8 Phase evolution of the correlated noise . ..