Session U16: Minisymposium: Low Radioactivity Background Techniques in Underground Experiments - III

TPC without charge multiplication : a CMOS direct readout towards neutrinoless double-beta decay and other applications.

High-pressure gaseous TPCs provide a unique combination of excellent energy resolution, event tracking for background discrimination, and scalability, which are ideal for neutrinoless double-beta decay searches. We are developing a pixelated charge readout plane filled with an array of CMOS sensors to harness the power of such a TPC. Each CMOS sensor has an exposed metal patch for direct charge collection and integrates charge sensitive amplifiers as well as signal processing and digitization/data transmission circuitry. The electronic noise is suppressed to a level that the required signal-to-noise ratio is achieved without the need of charge multiplication. It provides competitive energy resolution while improves on tracking capability, stability, and scalability compared to alternative readout schemes. Moreover, ions drifting in the gas can be read directly since the otherwise prohibitive ion avalanche is unnecessary. It enables the use of alternative gases and double-beta decay candidate isotopes such as $^{82}$SeF$_6$ gas, in which only ion drifting is possible. With modest modifications, the readout plane could be used in liquid noble gas and organic liquid TPCs for a broad range of applications. The design and the progress of the first prototype will be presented.   

Low Energy Noise Rejection with the Majorana Demonstrator

The \textsc{Majorana Demonstrator} is an array of P-type point contact germanium detectors enclosed in a low-background shield at the Sanford Underground Research Facility. Complementary to its search for the neutrinoless double beta decay of ${}^{76}$Ge are low energy rare event searches for dark matter and solar axions. In the initial run, 10 kg-y of data has been taken over a nearly two-year period. Though its detectors are routinely capable of sub-keV energy thresholds, electronics noise in the array presents a challenge to reliably discriminate physics signals from noise at the lowest energies. In this talk I discuss new noise rejection methods for the \textsc{Demonstrator}, employing maximum likelihood fits of each waveform and wavelet packet decomposition to maximize the detection potential for low energy physics searches.   

Performance of the MAJORANA Low-Mass Front-End in liquid cryogen

The next generation of neutrinoless double-beta decay experiments requires further reduction of backgrounds to maximize discovery potential. Using 76-Ge as a target, the LEGEND collaboration plans to achieve this through a combination of the low background materials employed by the MAJORANA DEMONSTRATOR, and the liquid argon active veto employed by GERDA. Given its low noise and world-leading low backgrounds, the MAJORANA Low-Mass Front-End (LMFE) is the baseline design for detector readout in LEGEND. However, as a component designed for use in a vacuum cryostat, its performance submerged in liquid cryogen must be evaluated. This talk will describe the MAJORANA LMFE, the testing performed to evaluate its performance in liquid cryogen, and the results of these tests.   

R\&D Status of Low Tc TES for CUPID Light Detectors

The Cryogenic Underground Observatory for Rare Events (CUORE) is a search for new physics via lepton number violation (LNV) currently operating at the Laboratori Nazionali del Gran Sasso (LNGS). CUORE utilizes 988 TeO$_2$ crystals (m = 742 kg) operated as cryogenic bolometers in an attempt to observe neutrinoless double beta decay ($0\nu\beta\beta$), and is expected to achieve a sensitivity to the $^{130}$Te $0\nu\beta\beta$ decay half-life of $T_{1/2} = 9$ x $10^{25}$ years (90 \% C.L.) after 5 years of operation. Beyond this, the CUORE Upgrade with Particle ID (CUPID) program is an attempt to extend the reach of a LNV search by introducing new detection strategies, lower background components, enhanced target masses, while making use of existing infrastructure from CUORE. CUPID will also allow for event by event discrimination, enhancing the ability to reject background. One such technique is to utilize sensitive light detectors that could measure scintillation light from the target mass. This talk will cover the current R\&D efforts at LBNL and UC Berkeley on CUPID and in particular the status of developing low-Tc transition edge sensors (TES) with SQUID readout for use in CUPID light detectors.   

Measurement of Light Emission in TeO$_2$ Crystals

CUPID (CUORE Upgrade with Particle ID) is a next-generation bolometric experiment that will search for $0\nu\beta\beta$ decay with enhanced sensitivity through the ability to distinguish between $0\nu\beta\beta$ events and $\alpha$ backgrounds by detecting light emissions. To achieve this, it is important to characterize the amount of Cherenkov radiation that we can expect to detect, as well as any other luminescence that particles may cause in the detector material. The CHErenkov/Scintillation Separation setup (CHESS) can detect light with high time resolution and is sensitive to the directionality of light escaping the target material. We use this setup to measure and distinguish between Cherenkov and scintillation-like light emitted in TeO$_2$ crystals, one of the primary candidate materials for the detector mass of CUPID.   

CUORE Noise Reduction using Decorrelation and Filtering

The Cryogenic Underground Observatory for Rare Events (CUORE) is a ton scale experimental search for 0$\nu\beta\beta$ decay on ${}^{130}$Te. The CUORE detector consists of 988 TeO$_2$ crystals operating at $\sim$15mK. CUORE sensitivity can be enhanced by both improving the resolution and by lowering the trigger thresholds leading to better rejection of multi-coincidence background events. Both these can be achieved via noise reduction: in this talk we present a method for the removal of multi-crystal correlated noise and its performance in terms of resolution improvement.   

Ultra low background DEAP-3600 detector: Is the secret ingredient Acrylic?

DEAP-3600 is a ton scale single-phase liquid argon detector operating 2 km underground at SNOLAB (Canada), and looking for WIMP with a mass higher than 100 GeV. Relying on the so-called argon scintillation pulse-shape discrimination to distinguish the electromagnetic background from the nuclear recoil signal, it has been designed as a background-free detector in the region of interest for 3 years of data. It has been taking data for over a year, and the first results have been published during the summer 2017. While the background-free goal cannot yet be demonstrated, it is already clear that DEAP-3600 achieved remarkably low levels of backgrounds. In particular, the $^{\mathrm{222}}$Rn contamination in the liquid argon was measured to be of the level of 0.2 $\mu $Bq/kg, significantly better than the best liquid Xenon detector. It is thanks in part to the use of acrylic for the detector vessel, a premiere for a cryostat. But acrylic alone would not have been enough. In this talk, I will present all the steps that have been needed to achieve these low background levels, from the material choices and assays to the surface treatments during construction and argon purification techniques.   

A study of high energy gamma intensities in $^{208}$Tl decay from a ThO$_{2}$ powder

The gamma decay intensities for E $>$ 3 MeV from $^{208}$Tl decay have very large uncertainties (100$\%$) in the NNDC database. New measurements with smaller uncertainties are desirable for understanding nuclear decay properties of the nucleus and high energy gamma background for other rare decay experiments. The AMoRE experiment, which is a neutrinoless double beta decay search with a Mo$_{100}$ (Q=3.034 MeV) based crystals at the YangYang Underground Laboratory (Y2L) in Korea, can be affected by the gammas over 3 MeV from the $^{208}$Tl. The High Purity Germanium (HPGe) group at the Center for Underground Physics (CUP) measured a 2kg ThO$_{2}$ powder with a 100$\%$ efficiency HPGe detector in the Y2L to obtain more accurate numbers of the high energy gamma intensities from $^{208}$Tl. A 10 cm thick lead plate was installed between the ThO$_{2}$ powder and the HPGe detector to block low energy gammas. The experimental set-up, Monte Carlo simulation results for detection efficiencies, and a preliminary result will be presented.