arXiv subjects

S. Mertens

Publications and source records attributed to S. Mertens.

At least 109 records · Page 6Linked to original sources

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↗

arXiv2015

MAJORANA Collaboration's Experience with Germanium Detectors

The goal of the \textsc{Majorana} \textsc{Demonstrator} project is to search for 0$νββ$ decay in $^{76}\mathrm{Ge}$. Of all candidate isotopes for 0$νββ$, $^{76}\mathrm{Ge}$ has some of the most favorable characteristics. Germanium detectors are a well established technology, and in searches for 0$νββ$, the high purity germanium crystal acts simultaneously as source and detector. Furthermore, p-type germanium detectors provide excellent energy resolution and a specially designed point contact geometry allows for sensitive pulse shape discrimination. This paper will summarize the experiences the \textsc{Majorana} collaboration made with enriched germanium detectors manufactured by ORTEC$^{\circledR}$. The process from production, to characterization and integration in \textsc{Majorana} mounting structure will be described. A summary of the performance of all enriched germanium detectors will be given.

physics.ins-det↗

arXiv2015

Wavelet Approach to Search for Sterile Neutrinos in Tritium $β$-Decay Spectra

Sterile neutrinos in the mass range of a few keV are candidates for both cold and warm dark matter. An ad-mixture of a heavy neutrino mass eigenstate to the electron neutrino would result in a minuscule distortion - a 'kink' - in a $β$-decay spectrum. In this paper we show that a wavelet transform is a very powerful shape analysis method to detect this signature. For a tritium source strength, similar to what is expected from the KATRIN experiment, a statistical sensitivity to active-to-sterile neutrino mixing down to $\sin^2 θ= 10^{-6}$ ($90\%$ CL) can be obtained after 3 years of measurement time. It is demonstrated that the wavelet approach is largely insensitive to systematic effects that result in smooth spectral modifications. To make full use of this analysis technique a high resolution measurement (FWHM of $\sim100$~eV) of the tritium $β$-decay spectrum is required.

hep-ph↗

arXiv2015

Status of the MAJORANA Demonstrator

The MAJORANA Collaboration is constructing the MAJORANA Demonstrator, an ultra-low background, 40-kg modular high purity Ge detector array to search for neutrinoless double-beta decay in Ge. In view of the next generation of tonne-scale Ge-based neutrinoless double-beta decay searches that will probe the neutrino mass scale in the inverted-hierarchy region, a major goal of the Demonstrator is to demonstrate a path forward to achieving a background rate at or below 1 count/tonne/year in the 4 keV region of interest around the Q-value at 2039 keV. The current status of the Demonstrator is discussed, as are plans for its completion.

physics.ins-det↗

arXiv2014

Sensitivity of Next-Generation Tritium Beta-Decay Experiments for keV-Scale Sterile Neutrinos

We investigate the sensitivity of tritium $β$-decay experiments for keV-scale sterile neutrinos. Relic sterile neutrinos in the keV mass range can contribute both to the cold and warm dark matter content of the universe. This work shows that a large-scale tritium beta-decay experiment, similar to the KATRIN experiment that is under construction, can reach a statistical sensitivity of the active-sterile neutrino mixing of $\sin^2θ\sim 10^{-8}$. The effect of uncertainties in the known theoretical corrections to the tritium $β$-decay spectrum were investigated, and found not to affect the sensitivity significantly. It is demonstrated that controlling uncorrelated systematic effects will be one of the main challenges in such an experiment.

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

A search for bremsstrahlung solar axions using the Majorana low-background BEGe detector at Kimballton (MALBEK)

A low-background, high-purity germanium detector has been used to search for evidence of low-energy, bremsstrahlung-generated solar axions. An upper bound of $1.36\times 10^{-11}$ $(95% CL)$ is placed on the direct coupling of DFSZ model axions to electrons. The prospects for the sensitivity of the Majorana Demonstrator array of point-contact germanium detectors to solar axions are discussed in the context of the model-independent annual modulation due to the seasonal variation of the earth-sun distance.

astro-ph.HE↗

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

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

Current Direct Neutrino Mass Experiments

In this contribution we review the status and perspectives of direct neutrino mass experiments. These experiments investigate the kinematics of $β$-decays of specific isotopes ($^3$H, $^{187}$Re, $^{163}$Ho) to derive model-independent information on the averaged electron (anti-) neutrino mass, which is formed by the incoherent sum of the neutrino mass eigenstates contributing to the electron neutrino. We first review the kinematics of $β$-decay and the determination of the neutrino mass, before giving a brief overview of past neutrino mass measurements (SN1987a-ToF studies, Mainz and Troitsk experiments for $^3$H, cryo-bolometers for $^{187}$Re). We then describe the Karlsruhe Tritium Neutrino (KATRIN) experiment which is currently under construction at Karlsruhe Institute of Technology. The large-scale setup will use the MAC-E-Filter principle pioneered earlier to push the sensitivity down to a value of 200 meV(90% C.L.). KATRIN faces many technological challenges that have to be resolved with regard to source intensity and stability, as well as precision energy analysis and low background rate close to the kinematic endpoint of tritium $β$-decay at 18.6 keV. We then review new experimental approaches such as the MARE, ECHO and Project8 experiments, which offer the promise to perform an independent measurement of the neutrino mass in the sub-eV region. This variety of methods and the novel technologies developed in all present and future experiments demonstrate the great potential of direct neutrino mass experiments in providing vital information on the absolute mass scale of neutrinos.

physics.ins-det↗

arXiv2013

Validation of a model for Radon-induced background processes in electrostatic spectrometers

The Karlsruhe Tritium Neutrino (KATRIN) experiment investigating tritium beta-decay close to the endpoint with unprecedented precision has stringent requirements on the background level of less than 10^(-2) counts per second. Electron emission during the alpha-decay of Rn-219 and Rn-220 atoms in the electrostatic spectrometers of KATRIN is a serious source of background exceeding this limit. In this paper we compare extensive simulations of Rn-induced background to specific measurements with the KATRIN pre-spectrometer to fully characterize the observed Rn-background rates and signatures and determine generic Rn emanation rates from the pre-spectrometer bulk material and its vacuum components.

physics.ins-det↗

arXiv2013

Modeling of electron emission processes accompanying Radon-$α$-decays within electrostatic spectrometers

Electrostatic spectrometers utilized in high-resolution beta-spectroscopy studies such as in the Karlsruhe Tritium Neutrino (KATRIN) experiment have to operate with a background level of less than 10^(-2) counts per second. This limit can be exceeded by even a small number of Rn-219 or Rn-220 atoms being emanated into the volume and undergoing alpha-decay there. In this paper we present a detailed model of the underlying background-generating processes via electron emission by internal conversion, shake-off and relaxation processes in the atomic shells of the Po-215 and Po-216 daughters. The model yields electron energy spectra up to 400 keV and electron multiplicities of up to 20 which are compared to experimental data.

physics.ins-det↗

arXiv2012

Stochastic Heating by ECR as a Novel Means of Background Reduction in the KATRIN Spectrometers

The primary objective of the KATRIN experiment is to probe the absolute neutrino mass scale with a sensitivity of 200 meV (90% C.L.) by precision spectroscopy of tritium beta-decay. To achieve this, a low background of the order of 10^(-2) cps in the region of the tritium beta-decay endpoint is required. Measurements with an electrostatic retarding spectrometer have revealed that electrons, arising from nuclear decays in the volume of the spectrometer, are stored over long time periods and thereby act as a major source of background exceeding this limit. In this paper we present a novel active background reduction method based on stochastic heating of stored electrons by the well-known process of electron cyclotron resonance (ECR). A successful proof-of-principle of the ECR technique was demonstrated in test measurements at the KATRIN pre-spectrometer, yielding a large reduction of the background rate. In addition, we have carried out extensive Monte Carlo simulations to reveal the potential of the ECR technique to remove all trapped electrons within negligible loss of measurement time in the main spectrometer. This would allow the KATRIN experiment attaining its full physics potential.

physics.ins-det↗

arXiv2012

Background due to stored electrons following nuclear decays in the KATRIN spectrometers and its impact on the neutrino mass sensitivity

The KATRIN experiment is designed to measure the absolute neutrino mass scale with a sensitivity of 200 meV at 90% C.L. by high resolution tritium beta-spectroscopy. A low background level of 10 mHz at the beta-decay endpoint is required in order to achieve the design sensitivity. In this paper we discuss a novel background source arising from magnetically trapped keV electrons in electrostatic retarding spectrometers. The main sources of these electrons are alpha-decays of the radon isotopes (219,220)Rn as well as beta-decays of tritium in the volume of the spectrometers. We characterize the expected background signal by extensive MC simulations and investigate the impact on the KATRIN neutrino mass sensitivity. From these results we refine design parameters for the spectrometer vacuum system and propose active background reduction methods to meet the stringent design limits for the overall background rate.

physics.ins-det↗

arXiv2012

The KATRIN Pre-Spectrometer at reduced Filter Energy

The KArlsruhe TRItium Neutrino experiment, KATRIN, will determine the mass of the electron neutrino with a sensitivity of 0.2 eV (90% C.L.) via a measurement of the beta-spectrum of gaseous tritium near its endpoint of E_0 =18.57 keV. An ultra-low background of about b = 10 mHz is among the requirements to reach this sensitivity. In the KATRIN main beam-line two spectrometers of MAC-E filter type are used in a tandem configuration. This setup, however, produces a Penning trap which could lead to increased background. We have performed test measurements showing that the filter energy of the pre-spectrometer can be reduced by several keV in order to diminish this trap. These measurements were analyzed with the help of a complex computer simulation, modeling multiple electron reflections both from the detector and the photoelectric electron source used in our test setup.

physics.ins-det↗