Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session H10: Tonne Scale Neutrinoless Double Beta Decay R&D IIIFocus
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Sponsoring Units: DNP DPF Chair: Andrea Pocar, University of Massachusetts, Amherst Room: Sheraton Governor's Square 12 |
Sunday, April 14, 2019 10:45AM - 11:21AM |
H10.00001: A Clear-Eyed View of Matter Creation: Beating Background in Neutrinoless Double-Beta Decay Searches Invited Speaker: Jason A Detwiler The first observation of the creation of matter in the laboratory in the form of neutrinoless double-beta (0νββ) decay may soon be within reach, with numerous high-exposure experiments using different, sensitive techniques either currently running, under construction, or being proposed. Each experiment faces a paramount challenge: deploying and observing enormous quantities of double-beta decay isotope without incurring significant background that could obfuscate a potential signal. I will discuss the primary categories and sources of background in these experiments, such as natural radioactivity, cosmic ray by-products, anthropogenic contamination, and even two-neutrino double-beta decay itself, which occurs at least O(105) times more frequently than 0νββ decay. I will then discuss the chief strategies and techniques used to mitigate background, such as passive shielding, active rejection, and multidimensional analysis, as well as design choices, administrative controls, and radioassay campaigns that intend to eliminate the presence of background sources from the outset. Finally, I'll quantify the impact of background on experimental sensitivities, highlighting the robustness of the present international program toward reaching its sensitivity goals, even while breaking new ground and fielding some of the lowest-background experiments in history. |
Sunday, April 14, 2019 11:21AM - 11:33AM |
H10.00002: Measurement of External Radioactive Backgrounds in the SNO+ Water Phase Anthony Zummo The SNO+ experiment has taken data with water and will search for neutrinoless double beta decay using 780 tonnes of tellurium loaded liquid scintillator. Because the rate of external radioactive backgrounds are not expected to change significantly between phases of SNO+, they can be measured in the water phase and used for sensitivity projections in future phases. These backgrounds are critical to the search for neutrinoless double beta decay as they are the dominant factor in the choice of fiducial volume. Two independent analyses were performed to measure the rate of the most significant external radioactive backgrounds, 208Tl and 214Bi. Both analyses find these rates to be consistent with expectations. |
Sunday, April 14, 2019 11:33AM - 11:45AM |
H10.00003: Surface Backgrounds in the Large Enriched Germanium Experiment for Neutrinoless Double beta decay (LEGEND) Bjoern Lehnert LEGEND searches for lepton number violation using high purity germanium detectors enriched in Ge76. These detectors are operated in a large volume of liquid argon (LAr) that provides cryogenic cooling, a low background environment, as well as an active scintillation veto for background rejection. LEGEND will use a variety of existing detectors from the GERDA and Majorana experiments and newly procured larger inverted coaxial p-type detectors. Past experience shows that, in LAr, surface backgrounds from alpha (Po210) and beta (K42) decays on the p+ and n+ electrodes are considerable backgrounds before analysis cuts. These backgrounds can be strongly reduced with pulse shape discrimination, which is highly dependent on the detector type, the fabrication procedure of the electrodes, as well as the instrumental noise in the final experimental configuration. Some of the detector types have never been extensively operated in LAr, and their response to LAr-borne surface backgrounds needs to be characterized prior to deployment. In this talk, I will discuss the surface backgrounds in LEGEND, including their pulse shape modeling, mitigation, and characterization plans. |
Sunday, April 14, 2019 11:45AM - 11:57AM |
H10.00004: Materials Radioassay Techniques for the nEXO Experiment O. Nusair for the nEXO Collaboration The University of Alabama Omar Nusair EXO-200 was a 200-kg-scale search for neutrinoless double-beta decay in isotopically enriched $^{136}$Xe, based on a single-phase liquid time projection chamber (TPC). nEXO is a 5000-kg-scale successor, presently in development, using a similar monolithic TPC concept. Both experiments require extremely low backgrounds, in order to achieve sensitivity targets on the order of $10^{26}$ and $10^{28}$ years, respectively. To this end, EXO-200 implemented a rigorous materials screening program prior to construction, in order to minimize intrinsic backgrounds from radioactivity in detector and shielding components. Operational data shows this approach to have been both effective in minimizing materials backgrounds and accurate in predicting overall detector backgrounds. nEXO has continued this campaign with even more stringent requirements. This talk will discuss radioassay techniques implemented by the nEXO collaboration. Constraints obtained by low-background gamma ray spectroscopy, neutron activation analysis, and mass spectrometry will be presented. |
Sunday, April 14, 2019 11:57AM - 12:09PM |
H10.00005: Investigation of Background Sources in CUORE Krystal Alfonso The Cryogenic Underground Observatory for Rare Events (CUORE) experiment is designed to search for the process of neutrinoless double-beta decay in 130Te. The signature of this process would manifest as a monoenergetic peak at the Q-value of the decay that, if observed, would confirm lepton number violation and the Majorana nature of the neutrino. As this is a process beyond the Standard Model and expected to be very rare, understanding the background sources in CUORE is essential to enhancing signal sensitivity. Using the geometry of the CUORE detector, which consists of a hexagonal array of 988 TeO2 bolometers, I will present my investigation of the positional dependence of the backgrounds in the array to identify localized background sources in CUORE. Implications on future generation of bolometer detectors for neutrinoless double-beta decay will also be discussed. |
Sunday, April 14, 2019 12:09PM - 12:21PM |
H10.00006: Cosmogenic Backgrounds in the MAJORANA DEMONSTRATOR Search for Neutrinoless Double-Beta Decay in 76Ge Andrew M Lopez Ultra-low background experiments such as the neutrinoless double-beta search in the MAJORANA DEMONSTRATOR and the future tonne-scale LEGEND experiment require a detailed understanding and minimization of all sources of background. An important method of minimizing muon-induced cosmogenic backgrounds is to build experiments in deep underground laboratories. A simulation campaign based on the GEANT4 and FLUKA codes provides an estimate of the cosmogenic background contributions to the MAJORANA DEMONSTRATOR, and is benchmarked by using data from the DEMONSTRATOR to validate the simulations. In this talk we discuss the details of the data analysis and simulation, the limitations of the campaign, and how this study benefits cosmogenic background estimation for the future LEGEND experiment. |
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