arXiv subjects

A. L. Hallin

Publications and source records attributed to A. L. Hallin.

At least 55 records · Page 3Linked to original sources

arXiv2018

Search for Zero-Neutrino Double Beta Decay in 76Ge with the Majorana Demonstrator

The \MJ\ Collaboration is operating an array of high purity Ge detectors to search for neutrinoless double-beta decay in $^{76}$Ge. The \MJ\ \DEM\ comprises 44.1~kg of Ge detectors (29.7 kg enriched in $^{76}$Ge) split between two modules contained in a low background shield at the Sanford Underground Research Facility in Lead, South Dakota. Here we present results from data taken during construction, commissioning, and the start of full operations. We achieve unprecedented energy resolution of 2.5 keV FWHM at \qval\ and a very low background with no observed candidate events in 10 kg yr of enriched Ge exposure, resulting in a lower limit on the half-life of $1.9\times10^{25}$ yr (90\% CL). This result constrains the effective Majorana neutrino mass to below 240 to 520 meV, depending on the matrix elements used. In our experimental configuration with the lowest background, the background is $4.0_{-2.5}^{+3.1}$ counts/(FWHM t yr).

nucl-ex↗

arXiv2017

The search for neutron-antineutron oscillations at the Sudbury Neutrino Observatory

Tests on $B-L$ symmetry breaking models are important probes to search for new physics. One proposed model with $Δ(B-L)=2$ involves the oscillations of a neutron to an antineutron. In this paper a new limit on this process is derived for the data acquired from all three operational phases of the Sudbury Neutrino Observatory experiment. The search was concentrated in oscillations occurring within the deuteron, and 23 events are observed against a background expectation of 30.5 events. These translate to a lower limit on the nuclear lifetime of $1.48\times 10^{31}$ years at 90% confidence level (CL) when no restriction is placed on the signal likelihood space (unbounded). Alternatively, a lower limit on the nuclear lifetime was found to be $1.18\times 10^{31}$ years at 90% CL when the signal was forced into a positive likelihood space (bounded). Values for the free oscillation time derived from various models are also provided in this article. This is the first search for neutron-antineutron oscillation with the deuteron as a target.

hep-ex↗

arXiv2016

Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy beta and nuclear recoils in liquid argon with DEAP-1

The DEAP-1 low-background liquid argon detector was used to measure scintillation pulse shapes of electron and nuclear recoil events and to demonstrate the feasibility of pulse-shape discrimination (PSD) down to an electron-equivalent energy of 20 keV. In the surface dataset using a triple-coincidence tag we found the fraction of beta events that are misidentified as nuclear recoils to be $<1.4\times 10^{-7}$ (90% C.L.) for energies between 43-86 keVee and for a nuclear recoil acceptance of at least 90%, with 4% systematic uncertainty on the absolute energy scale. The discrimination measurement on surface was limited by nuclear recoils induced by cosmic-ray generated neutrons. This was improved by moving the detector to the SNOLAB underground laboratory, where the reduced background rate allowed the same measurement with only a double-coincidence tag. The combined data set contains $1.23\times10^8$ events. One of those, in the underground data set, is in the nuclear-recoil region of interest. Taking into account the expected background of 0.48 events coming from random pileup, the resulting upper limit on the electronic recoil contamination is $<2.7\times10^{-8}$ (90% C.L.) between 44-89 keVee and for a nuclear recoil acceptance of at least 90%, with 6% systematic uncertainty on the absolute energy scale. We developed a general mathematical framework to describe PSD parameter distributions and used it to build an analytical model of the distributions observed in DEAP-1. Using this model, we project a misidentification fraction of approx. $10^{-10}$ for an electron-equivalent energy threshold of 15 keV for a detector with 8 PE/keVee light yield. This reduction enables a search for spin-independent scattering of WIMPs from 1000 kg of liquid argon with a WIMP-nucleon cross-section sensitivity of $10^{-46}$ cm$^2$, assuming negligible contribution from nuclear recoil backgrounds.

astro-ph.IM↗

arXiv2016

A precise method to determine the activity of a weak neutron source using a germanium detector

A standard high purity germanium (HPGe) detector was used to determine the previously unknown neutron activity of a weak americium-beryllium (AmBe) neutron source. Gamma rays were created through 27Al(n,n'), 27Al(n,gamma) and 1H(n,gamma) reactions induced by the neutrons on aluminum and acrylic disks, respectively. These gamma rays were measured using the HPGe detector. Given the unorthodox experimental arrangement, a Monte Carlo simulation was developed to model the efficiency of the detector system to determine the neutron activity from the measured gamma rays. The activity of our neutron source was determined to be 307.4 +/- 5.0 n/s and is consistent for the different neutron-induced gamma rays.

physics.ins-det↗

arXiv2016

Current Status and Future Prospects of the SNO+ Experiment

SNO+ is a large liquid scintillator-based experiment located 2km underground at SNOLAB, Sudbury, Canada. It reuses the Sudbury Neutrino Observatory detector, consisting of a 12m diameter acrylic vessel which will be filled with about 780 tonnes of ultra-pure liquid scintillator. Designed as a multipurpose neutrino experiment, the primary goal of SNO+ is a search for the neutrinoless double-beta decay (0$νββ$) of 130Te. In Phase I, the detector will be loaded with 0.3% natural tellurium, corresponding to nearly 800 kg of 130Te, with an expected effective Majorana neutrino mass sensitivity in the region of 55-133 meV, just above the inverted mass hierarchy. Recently, the possibility of deploying up to ten times more natural tellurium has been investigated, which would enable SNO+ to achieve sensitivity deep into the parameter space for the inverted neutrino mass hierarchy in the future. Additionally, SNO+ aims to measure reactor antineutrino oscillations, low-energy solar neutrinos, and geoneutrinos, to be sensitive to supernova neutrinos, and to search for exotic physics. A first phase with the detector filled with water will begin soon, with the scintillator phase expected to start after a few months of water data taking. The 0$νββ$ Phase I is foreseen for 2017.

physics.ins-det↗

arXiv2015

DEAP-3600 Dark Matter Search

The DEAP-3600 experiment is located 2 km underground at SNOLAB, in Sudbury, Ontario. It is a single-phase detector that searches for dark matter particle interactions within a 1000-kg fiducial mass target of liquid argon. A first generation prototype detector (DEAP-1) with a 7-kg liquid argon target mass demonstrated a high level of pulse-shape discrimination (PSD) for reducing $β$/$γ$ backgrounds and helped to develop low radioactivity techniques to mitigate surface-related $α$ backgrounds. Construction of the DEAP-3600 detector is nearly complete and commissioning is starting in 2014. The target sensitivity to spin-independent scattering of Weakly Interacting Massive Particles (WIMPs) on nucleons of 10$^{-46}$ cm$^2$ will allow one order of magnitude improvement in sensitivity over current searches at 100 GeV WIMP mass. This paper presents an overview and status of the DEAP-3600 project and discusses plans for a future multi-tonne experiment, DEAP-50T.

physics.ins-det↗

arXiv2015

The Majorana Parts Tracking Database

The Majorana Demonstrator is an ultra-low background physics experiment searching for the neutrinoless double beta decay of $^{76}$Ge. The Majorana Parts Tracking Database is used to record the history of components used in the construction of the Demonstrator. The tracking implementation takes a novel approach based on the schema-free database technology CouchDB. Transportation, storage, and processes undergone by parts such as machining or cleaning are linked to part records. Tracking parts provides a great logistics benefit and an important quality assurance reference during construction. In addition, the location history of parts provides an estimate of their exposure to cosmic radiation. A web application for data entry and a radiation exposure calculator have been developed as tools for achieving the extreme radio-purity required for this rare decay search.

physics.ins-det↗

arXiv2014

Improving Photoelectron Counting and Particle Identification in Scintillation Detectors with Bayesian Techniques

Many current and future dark matter and neutrino detectors are designed to measure scintillation light with a large array of photomultiplier tubes (PMTs). The energy resolution and particle identification capabilities of these detectors depend in part on the ability to accurately identify individual photoelectrons in PMT waveforms despite large variability in pulse amplitudes and pulse pileup. We describe a Bayesian technique that can identify the times of individual photoelectrons in a sampled PMT waveform without deconvolution, even when pileup is present. To demonstrate the technique, we apply it to the general problem of particle identification in single-phase liquid argon dark matter detectors. Using the output of the Bayesian photoelectron counting algorithm described in this paper, we construct several test statistics for rejection of backgrounds for dark matter searches in argon. Compared to simpler methods based on either observed charge or peak finding, the photoelectron counting technique improves both energy resolution and particle identification of low energy events in calibration data from the DEAP-1 detector and simulation of the larger MiniCLEAN dark matter detector.

physics.ins-det↗

arXiv2014

A Dark Matter Search with MALBEK

The MAJORANA DEMONSTRATOR is an array of natural and enriched high purity germanium detectors that will search for the neutrinoless double-beta decay of 76-Ge and perform a search for weakly interacting massive particles (WIMPs) with masses below 10 GeV. As part of the MAJORANA research and development efforts, we have deployed a modified, low-background broad energy germanium detector at the Kimballton Underground Research Facility. With its sub-keV energy threshold, this detector is sensitive to potential non-Standard Model physics, including interactions with WIMPs. We discuss the backgrounds present in the WIMP region of interest and explore the impact of slow surface event contamination when searching for a WIMP signal.

nucl-ex↗

arXiv2014

Background Model for the Majorana Demonstrator

The Majorana Collaboration is constructing a system containing 40 kg of HPGe detectors to demonstrate the feasibility and potential of a future tonne-scale experiment capable of probing the neutrino mass scale in the inverted-hierarchy region. To realize this, a major goal of the Majorana Demonstrator is to demonstrate a path forward to achieving a background rate at or below 1 cnt/(ROI-t-y) in the 4 keV region of interest around the Q-value at 2039 keV. This goal is pursued through a combination of a significant reduction of radioactive impurities in construction materials with analytical methods for background rejection, for example using powerful pulse shape analysis techniques profiting from the p-type point contact HPGe detectors technology. The effectiveness of these methods is assessed using simulations of the different background components whose purity levels are constrained from radioassay measurements.

physics.ins-det↗

arXiv2014

Testing the Ge detectors for the MAJORANA DEMONSTRATOR

High purity germanium (HPGe) crystals will be used for the MAJORANA DEMONSTRATOR, where they serve as both the source and the detector for neutrinoless double beta decay. It is crucial for the experiment to understand the performance of the HPGe crystals. A variety of crystal properties are being investigated, including basic properties such as energy resolution, efficiency, uniformity, capacitance, leakage current and crystal axis orientation, as well as more sophisticated properties, e.g. pulse shapes and dead layer and transition layer distributions. In this paper, we will present our measurements that characterize the HPGe crystals. We will also discuss our simulation package for the detector characterization setup, and show that additional information can be extracted from data-simulation comparisons.

physics.ins-det↗

arXiv2014

Radon backgrounds in the DEAP-1 liquid-argon-based Dark Matter detector

The DEAP-1 \SI{7}{kg} single phase liquid argon scintillation detector was operated underground at SNOLAB in order to test the techniques and measure the backgrounds inherent to single phase detection, in support of the \mbox{DEAP-3600} Dark Matter detector. Backgrounds in DEAP are controlled through material selection, construction techniques, pulse shape discrimination and event reconstruction. This report details the analysis of background events observed in three iterations of the DEAP-1 detector, and the measures taken to reduce them. The $^{222}$Rn decay rate in the liquid argon was measured to be between 16 and \SI{26}{\micro\becquerel\per\kilogram}. We found that the background spectrum near the region of interest for Dark Matter detection in the DEAP-1 detector can be described considering events from three sources: radon daughters decaying on the surface of the active volume, the expected rate of electromagnetic events misidentified as nuclear recoils due to inefficiencies in the pulse shape discrimination, and leakage of events from outside the fiducial volume due to imperfect position reconstruction. These backgrounds statistically account for all observed events, and they will be strongly reduced in the DEAP-3600 detector due to its higher light yield and simpler geometry.

astro-ph.IM↗

arXiv2013

Status of the MAJORANA DEMONSTRATOR experiment

The MAJORANA DEMONSTRATOR neutrinoless double beta-decay experiment is currently under construction at the Sanford Underground Research Facility in South Dakota, USA. An overview and status of the experiment are given.

physics.ins-det↗

arXiv2013

A Search for Astrophysical Burst Signals at the Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) has confirmed the standard solar model and neutrino oscillations through the observation of neutrinos from the solar core. In this paper we present a search for neutrinos associated with sources other than the solar core, such as gamma-ray bursters and solar flares. We present a new method for looking for temporal coincidences between neutrino events and astrophysical bursts of widely varying intensity. No correlations were found between neutrinos detected in SNO and such astrophysical sources.

astro-ph.SR↗

arXiv2013

The {\sc Majorana Demonstrator} Neutrinoless Double-Beta Decay Experiment

The {\sc Majorana Demonstrator will search for the neutrinoless double-beta decay of the isotope Ge-76 with a mixed array of enriched and natural germanium detectors. The observation of this rare decay would indicate the neutrino is its own antiparticle, demonstrate that lepton number is not conserved, and provide information on the absolute mass scale of the neutrino. The {\sc Demonstrator} is being assembled at the 4850-foot level of the Sanford Underground Research Facility in Lead, South Dakota. The array will be situated in a low-background environment and surrounded by passive and active shielding. Here we describe the science goals of the {\sc Demonstrator} and the details of its design.

physics.ins-det↗

arXiv2013

The MAJORANA DEMONSTRATOR: A Search for Neutrinoless Double-beta Decay of Germanium-76

The {\sc Majorana} collaboration is searching for neutrinoless double beta decay using $^{76}$Ge, which has been shown to have a number of advantages in terms of sensitivities and backgrounds. The observation of neutrinoless double-beta decay would show that lepton number is violated and that neutrinos are Majorana particles and would simultaneously provide information on neutrino mass. Attaining sensitivities for neutrino masses in the inverted hierarchy region, $15 - 50$ meV, will require large, tonne-scale detectors with extremely low backgrounds, at the level of $\sim$1 count/t-y or lower in the region of the signal. The {\sc Majorana} collaboration, with funding support from DOE Office of Nuclear Physics and NSF Particle Astrophysics, is constructing the {\sc Demonstrator}, an array consisting of 40 kg of p-type point-contact high-purity germanium (HPGe) detectors, of which $\sim$30 kg will be enriched to 87% in $^{76}$Ge. The {\sc Demonstrator} is being constructed in a clean room laboratory facility at the 4850' level (4300 m.w.e.) of the Sanford Underground Research Facility (SURF) in Lead, SD. It utilizes a compact graded shield approach with the inner portion consisting of ultra-clean Cu that is being electroformed and machined underground. The primary aim of the {\sc Demonstrator} is to show the feasibility of a future tonne-scale measurement in terms of backgrounds and scalability.

physics.ins-det↗

arXiv2013

Depth Requirements for a Tonne-scale 76Ge Neutrinoless Double-beta Decay Experiment

Neutrinoless double-beta decay experiments can potentially determine the Majorana or Dirac nature of the neutrino, and aid in understanding the neutrino absolute mass scale and hierarchy. Future 76Ge-based searches target a half-life sensitivity of >10^27 y to explore the inverted neutrino mass hierarchy. Reaching this sensitivity will require a background rate of <1 count tonne^-1 y^-1 in a 4-keV-wide spectral region of interest surrounding the Q value of the decay. We investigate the overburden required to reach this background goal in a tonne-scale experiment with a compact (copper and lead) shield based on Monte Carlo calculations of cosmic-ray background rates. We find that, in light of the presently large uncertainties in these types of calculations, a site with an underground depth >~5200 mwe is required for a tonne-scale experiment with a compact shield similar to the planned 40-kg MAJORANA DEMONSTRATOR. The required overburden is highly dependent on the chosen shielding configuration and could be relaxed significantly if, for example, a liquid cryogen and water shield, or an active neutron shield were employed. Operation of the MAJORANA DEMONSTRATOR and GERDA detectors will serve to reduce the uncertainties on cosmic-ray background rates and will impact the choice of shielding style and location for a future tonne-scale experiment. 4/2013: The peer review process revealed that one of the veto rejection factors (the factor-of-4 described on p12) needs to be better established. Our reevaluation of this parameter to date has not yielded strong support for the value stated in the manuscript, and we require further study to develop a solid estimate. This further study will supersede the work described in this manuscript, and may or may not lead to the same conclusion regarding the ~>5200 mwe requirement for future tonne-scale 76Ge neutrinoless double beta decay experiments.

nucl-ex↗

arXiv2012

The MAJORANA DEMONSTRATOR: Progress towards showing the feasibility of a tonne-scale 76Ge neutrinoless double-beta decay experiment

The MAJORANA DEMONSTRATOR will search for the neutrinoless double-beta decay of the 76Ge isotope with a mixed array of enriched and natural germanium detectors. The observation of this rare decay would indicate the neutrino is its own anti-particle, demonstrate that lepton number is not conserved, and provide information on the absolute mass-scale of the neutrino. The DEMONSTRATOR is being assembled at the 4850 foot level of the Sanford Underground Research Facility in Lead, South Dakota. The array will be contained in a low-background environment and surrounded by passive and active shielding. The goals for the DEMONSTRATOR are: demonstrating a background rate less than 3 t$^{-1}$ y$^{-1}$ in the 4 keV region of interest (ROI) surrounding the 2039 keV 76Ge endpoint energy; establishing the technology required to build a tonne-scale germanium based double-beta decay experiment; testing the recent claim of observation of neutrinoless double-beta decay [H. V. Klapdor-Kleingrothaus and I. V. Krivosheina, Mod. Phys. Lett. A21, 1547 (2006)]; and performing a direct search for light WIMPs (3-10 GeV).

nucl-ex↗