Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session L10: Tonne Scale Neutrinoless Double Beta Decay R&D V |
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Sponsoring Units: DNP DPF Chair: Reina Maruyama, Yale University Room: Sheraton Governor's Square 12 |
Sunday, April 14, 2019 3:30PM - 3:42PM |
L10.00001: Design of the calibration system for LEGEND Ralph J Massarczyk The Large Enriched Germanium Experiment for Neutrinoless Double-beta decay (LEGEND) is an experimental effort to search for neutrinoless double-beta decay in 76Ge. Using a phased approach, the collaboration aims to develop an experimental program with the discovery potential reaching a half-life up to 1028 years or longer. In the first 200-kg phase, LEGEND will use existing resources as appropriate to expedite physics results. |
Sunday, April 14, 2019 3:42PM - 3:54PM |
L10.00002: Calibration Techniques for the nEXO Experiment Erin Hansen The nEXO experiment will search for neutrinoless double beta decay of 136Xe using 5 tonnes of enriched liquid xenon in a low-background single-phase time projection chamber. nEXO is expected to reach a 10 year sensitivity of ~1028 years. This talk will discuss techniques for light and charge calibration currently under study by the nEXO collaboration, including results from testing and simulation of dissolved calibration sources capable of characterizing the center of nEXO's large drift chamber, complemented by liquid xenon fluid simulations. External gamma and neutron sources are also studied. |
Sunday, April 14, 2019 3:54PM - 4:06PM |
L10.00003: An Internal-Source Scanning Cryostat for HPGe Detectors Gulden Othman LEGEND is a next-generation search for neutrinoless double-beta decay in 76Ge which will incorporate successful aspects of the current-generation experiments, the MAJORANA DEMONSTRATOR and GERDA. In addition to new detector designs, LEGEND will utilize the 76Ge-enriched high-purity germanium (HPGe) detectors currently in use in MAJORANA and GERDA. The MAJORANA DEMONSTRATOR employs HPGe detectors of a P-type Point Contact (PPC) geometry. Passivated surfaces on the MAJORANA PPCs makes them susceptible to surface backgrounds, such as alphas, which can potentially contaminate the region of interest for neutrinoless double-beta decay. Understanding the detector response to these surface backgrounds is crucial in both current and next-generation 76Ge neutrinoless double-beta decay searches. This talk will focus on R&D efforts underway to examine the response of the passivated surface of MAJORANA-style PPCs to surface backgrounds in dedicated test stands using collimated alpha, beta, and gamma sources. |
Sunday, April 14, 2019 4:06PM - 4:18PM |
L10.00004: Cryogenic Electronics Readout for the nEXO Experiment Eric Raguzin The next Enriched Xenon Observatory (nEXO) is a proposed 5-ton monolithic liquid xenon TPC searching for evidence of the neutrinoless double beta decay of 136Xe. The sensitivity approaches T1/2 = 1028 years, and the current energy resolution benchmark is <1%. The required energy resolution calls for the use of cryogenic electronics to perform functions from signal collection to digitization for both charge and scintillation measurement. In situ cold electronics minimizes capacitance, electromagnetic interference, transistor noise, and feedthrough/cabling material. Similar cold electronic readouts have been successfully implemented in the MicroBooNE and protoDUNE experiments, validating the design concept. However, neither of these experiments necessitated radiopurity limitations. The addition of the radiopurity requirement informs the design in every aspect, from IC packaging and design to the substrate material to the interconnections and design of the collection tile. This talk will present an overview of the evolution of cold electronics and the current design considerations and progress of cryogenic electronics readout for nEXO. |
Sunday, April 14, 2019 4:18PM - 4:30PM |
L10.00005: An Electro-thermal Response Model of CUORE Bolometers Mingyu Li CUORE (Cryogenic Underground Observatory for Rare Events) is an ongoing tonne-scale search for 0νββ decay in 130Te implementing Neutron Transmutation Doped (NTD) Germanium as thermistors. The experiment contains a total of 741 kg TeO2 crystals and operates at a cryogenic temperature of around 10 mK. While there have been efforts in modeling the electro-thermal system in the precursor experiment CUORE-0, it is essential to build and test another one for CUORE to further understand key thermal interfaces that determine the quality of the pulse signal. We present an idealized electro-thermal pulse response model using the NTD Ge Voltage-Current data in thermal equilibrium. The model is fitted to normalized real-time pulses in 78 CUORE channels for validation and extraction of interested parameter values, such as crystal-NTD thermal conductance and crystal-heatsink thermal conductance. The application of the analytical response curve in the optimal filter for each channel is expected to further improve the current energy resolution of 8 keV in the region of interest. A similar model can be adopted in future detector R&D of CUORE Upgrade with Particle Identification. |
Sunday, April 14, 2019 4:30PM - 4:42PM |
L10.00006: Characterization of an Ionization Readout Tile for nEXO Michael J Jewell A new design for the anode of a time projection chamber, consisting of a charge-detecting "tile", is investigated for use in the proposed tonne-scale nEXO experiment to search for neutrinoless double-beta decay. Modular by design, an array of tiles can cover a sizable area. The width of each strip is small compared to the size of the tile, so a Frisch grid is not required. A grid-less, tiled anode design is beneficial for an experiment such as nEXO, where a wire tensioning support structure and Frisch grid might contribute radioactive backgrounds and would have to be designed to accommodate cycling to cryogenic temperatures. A prototype tile was tested in a cell containing liquid xenon. Very good agreement is achieved between the measured ionization spectrum of a 207Bi source and simulations giving an energy resolution comparable to the best intrinsic ionization-only resolution necessary to achieve the expected energy resolution σ/Qββ of 1 %. |
Sunday, April 14, 2019 4:42PM - 4:54PM |
L10.00007: Developing planar detectors for studying contact properties in liquid argon Rajendra Panth, Wenzhao Wei, Xianghua Meng, Guojian Wang, Hao Mei, Jing Liu, Gang Yang, Dongming Mei Electrical contact property is an important parameter for a germanium detector. The stability of electrical contact when directly immersed in liquid argon (LAr) is important for LEGEND-type detectors dedicated to measuring neutrinoless double-beta decay using 76Ge as a target. LAr also acts as an active shield for backgrounds. Cosmic rays and gamma radiation that does not fully deposit their energy in the germanium detector can be rejected with LAr scintillation light veto. Ultra-high purity LAr helps to improve light yield and attenuation of the noise signal. This can help to reduce the background level. Background reduction in the search for neutrinoless double beta decay is crucial to reach the higher sensitivity limit on half-life. We plan to study the background rejection and contact properties of a planar germanium detector immersed in the LAr at MPI this summer and compare it to operating at LN temperature at USD. |
Sunday, April 14, 2019 4:54PM - 5:06PM |
L10.00008: Signal-background Discrimination in EXO-200 with Deep Learning Thomas H Richards We develop a deep neural network (DNN) algorithm to discriminate signal and background events in the EXO-200 neutrinoless double beta decay experiment. In the studied case, the DNN is able to classify Monte Carlo events as signal (neutrinoless double beta decay of 136Xe) or different backgrounds directly from the waveforms. The classification accuracy exceeds that of conventional algorithms used in the experiment, trained over the same data. The accuracy of background classification is checked with real detector calibration data for the most important background types (gamma decays of 238U/232Th decay chains and 60Co, two-neutrino double beta decay of 136Xe, beta decay of 137Xe). Additional checks to substantiate the validity of the network’s performance will be presented. |
Sunday, April 14, 2019 5:06PM - 5:18PM |
L10.00009: Characterizing Germanium (Ge) Crystals for Developing Ge detectors Mathbar Singh Raut, Sanjay Bhattarai, Jing Liu, Hao Mei, Dongming Mei, Gang Yang, Guojian Wang The carrier concentration, the mobility of the charge carriers and the resistivity are some of the key electrical properties which are used to determine the quality of the grown HPGe crystals in the laboratory. A Vander Pauw Hall - Effect measurement system is used to measure the above mentioned electrical properties. We study the systematic error in measuring electrical properties using the Hall Effect with samples cut into different shapes. An optical microscope (Nikon Eclipse LV150L) is used to observe and count dislocations to calculate the dislocation density. We report the systematic errors in Hall Effect measurements that will impact the detector performance. This work is supported by NSF OISE-1743790 and NSF PHY-1902577. |
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