S. Mertens - Otto-von-Guericke University Magdeburg and Santa Fe Institute

S. Mertens
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S. Mertens
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Otto-von-Guericke University Magdeburg and Santa Fe Institute
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Physics - Instrumentation and Detectors (36)
 
Nuclear Experiment (25)
 
High Energy Physics - Experiment (11)
 
High Energy Physics - Phenomenology (6)
 
Physics - Statistical Mechanics (5)
 
Cosmology and Nongalactic Astrophysics (4)
 
Mathematics - Combinatorics (4)
 
Physics - Disordered Systems and Neural Networks (3)
 
Physics - Materials Science (3)
 
High Energy Astrophysical Phenomena (1)
 
Computer Science - Data Structures and Algorithms (1)
 
Computer Science - Computational Geometry (1)
 
Mathematics - Probability (1)
 
Computer Science - Computational Complexity (1)
 
Mathematics - Optimization and Control (1)
 
Mathematical Physics (1)
 
Mathematics - Mathematical Physics (1)
 
Astrophysics of Galaxies (1)
 
Physics - Computational Physics (1)

Publications Authored By S. Mertens

We derive formulas for the number of polycubes of size $n$ and perimeter $t$ that are proper in $n-1$ and $n-2$ dimensions. These formulas complement computer based enumerations of perimeter polynomials in percolation problems. We demonstrate this by computing the perimeter polynomial for $n=12$ in arbitrary dimension $d$. Read More

We study the annealing stability of bottom-pinned perpendicularly magnetized magnetic tunnel junctions based on dual MgO free layers and thin fixed systems comprising a hard [Co/Ni] multilayer antiferromagnetically coupled to thin a Co reference layer and a FeCoB polarizing layer. Using conventional magnetometry and advanced broadband ferromagnetic resonance, we identify the properties of each sub-unit of the magnetic tunnel junction and demonstrate that this material option can ensure a satisfactory resilience to the 400$^\circ$C thermal annealing needed in solid-state magnetic memory applications. The dual MgO free layer possesses an anneal-robust 0. Read More

[Co/Ni] multilayers with perpendicular magnetic anisotropy (PMA) have been researched and applied in various spintronic applications. Typically the seed layer material is studied to provide the desired face-centered cubic (\textit{fcc}) texture to the [Co/Ni] to obtain PMA. The integration of [Co/Ni] in back-end-of-line (BEOL) processes also requires the PMA to survive post-annealing. Read More

We present new limits on exotic keV-scale physics based on 478 kg d of MAJORANA DEMONSTRATOR commissioning data. Constraints at the 90% confidence level are derived on bosonic dark matter (DM) and solar axion couplings, Pauli exclusion principle violating (PEPV) decay, and electron decay using monoenergetic peak signal-limits above our background. Our most stringent DM constraints are set for 11. Read More

The Kassiopeia particle tracking framework is an object-oriented software package using modern C++ techniques, written originally to meet the needs of the KATRIN collaboration. Kassiopeia features a new algorithmic paradigm for particle tracking simulations which targets experiments containing complex geometries and electromagnetic fields, with high priority put on calculation efficiency, customizability, extensibility, and ease of use for novice programmers. To solve Kassiopeia's target physics problem the software is capable of simulating particle trajectories governed by arbitrarily complex differential equations of motion, continuous physics processes that may in part be modeled as terms perturbing that equation of motion, stochastic processes that occur in flight such as bulk scattering and decay, and stochastic surface processes occuring at interfaces, including transmission and reflection effects. Read More

A search for Pauli-exclusion-principle-violating K-alpha electron transitions was performed using 89.5 kg-d of data collected with a p-type point contact high-purity germanium detector operated at the Kimballton Underground Research Facility. A lower limit on the transition lifetime of 5. Read More

The Majorana Demonstrator searches for neutrinoless double-beta decay of $^{76}$Ge using arrays of high-purity germanium detectors. If observed, this process would demonstrate that lepton number is not a conserved quantity in nature, with implications for grand-unification and for explaining the predominance of matter over antimatter in the universe. A problematic background in such large granular detector arrays is posed by alpha particles. Read More

Neutrinoless double-beta decay searches seek to determine the nature of neutrinos, the existence of a lepton violating process, and the effective Majorana neutrino mass. The {\sc Majorana} Collaboration is assembling an array of high purity Ge detectors to search for neutrinoless double-beta decay in $^{76}$Ge. The {\sc Majorana Demonstrator} is composed of 44. Read More

The MAJORANA Collaboration is constructing a system containing 44 kg of high-purity Ge (HPGe) detectors to demonstrate the feasibility and potential of a future tonne-scale experiment capable of probing the neutrino mass scale to ~15 meV. 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 count/(ROI-t-y) in the 4 keV region of interest (ROI) around the Q-value at 2039 keV. This goal is pursued through a combination of a significant reduction of radioactive impurities in construction materials and analytical methods for background rejection, for example using powerful pulse shape analysis techniques profiting from the p-type point contact HPGe detectors technology. Read More

We study the properties of composite free layers with perpendicular anisotropy. The free layers are made of a soft FeCoB layer ferromagnetically coupled by a variable spacer (Ta, W, Mo) to a very anisotropic [Co/Ni] multilayer embodied in a magnetic tunnel junction meant for spin torque memory applications. For this we use broadband ferromagnetic resonance to follow the field dependence of the acoustical and optical excitation of the composite free layer in both in-plane and out-of-plane applied fields. Read More

We investigate a new method to search for keV-scale sterile neutrinos that could account for Dark Matter. Neutrinos trapped in our galaxy could be captured on stable $^{163}$Dy if their mass is greater than 2.83 keV. Read More

ADC non-linearities are a major systematic effect in the search for keV-scale sterile neutrinos with tritium $\beta$-decay experiments like KATRIN. They can significantly distort the spectral shape and thereby obscure the tiny kink-like signature of a sterile neutrino. In this work we demonstrate various mitigation techniques to reduce the impact of ADC non-linearities on the tritium $\beta$-decay spectrum to a level of $<$ ppm. Read More

With a mass at least six orders of magnitudes smaller than the mass of an electron -- but non-zero -- neutrinos are a clear misfit in the Standard Model of Particle Physics. On the one hand, its tiny mass makes the neutrino one of the most interesting particles, one that might hold the key to physics beyond the Standard Model. On the other hand this minute mass leads to great challenges in its experimental determination. Read More

The MAJORANA Collaboration is constructing the MAJORANA Demonstrator, an ultra-low background, 44-kg modular high-purity Ge (HPGe) detector array to search for neutrinoless double-beta decay in Ge-76. The phenomenon of surface micro-discharge induced by high-voltage has been studied in the context of the MAJORANA Demonstrator. This effect can damage the front-end electronics or mimic detector signals. Read More

We derive an exact, simple relation between the average number of clusters and the wrapping probabilities for two-dimensional percolation. The relation holds for periodic lattices of any size. It generalizes a classical result of Sykes and Essam and it can be used to find exact or very accurate approximations of the critical density. Read More

2016Mar
Authors: M. Arenz, M. Babutzka, M. Bahr, J. P. Barrett, S. Bauer, M. Beck, A. Beglarian, J. Behrens, T. Bergmann, U. Besserer, J. Blümer, L. I. Bodine, K. Bokeloh, J. Bonn, B. Bornschein, L. Bornschein, S. Büsch, T. H. Burritt, S. Chilingaryan, T. J. Corona, L. De Viveiros, P. J. Doe, O. Dragoun, G. Drexlin, S. Dyba, S. Ebenhöch, K. Eitel, E. Ellinger, S. Enomoto, M. Erhard, D. Eversheim, M. Fedkevych, A. Felden, S. Fischer, J. A. Formaggio, F. Fränkle, D. Furse, M. Ghilea, W. Gil, F. Glück, A. Gonzalez Urena, S. Görhardt, S. Groh, S. Grohmann, R. Grössle, R. Gumbsheimer, M. Hackenjos, V. Hannen, F. Harms, N. Hauÿmann, F. Heizmann, K. Helbing, W. Herz, S. Hickford, D. Hilk, B. Hillen, T. Höhn, B. Holzapfel, M. Hötzel, M. A. Howe, A. Huber, A. Jansen, N. Kernert, L. Kippenbrock, M. Kleesiek, M. Klein, A. Kopmann, A. Kosmider, A. Kovalík, B. Krasch, M. Kraus, H. Krause, M. Krause, L. Kuckert, B. Kuffner, L. La Cascio, O. Lebeda, B. Leiber, J. Letnev, V. M. Lobashev, A. Lokhov, E. Malcherek, M. Mark, E. L. Martin, S. Mertens, S. Mirz, B. Monreal, K. Müller, M. Neuberger, H. Neumann, S. Niemes, M. Noe, N. S. Oblath, A. Off, H. -W. Ortjohann, A. Osipowicz, E. Otten, D. S. Parno, P. Plischke, A. W. P. Poon, M. Prall, F. Priester, P. C. -O. Ranitzsch, J. Reich, O. Rest, R. G. H. Robertson, M. Röllig, S. Rosendahl, S. Rupp, M. Rysavy, K. Schlösser, M. Schlösser, K. Schönung, M. Schrank, J. Schwarz, W. Seiler, H. Seitz-Moskaliuk, J. Sentkerestiova, A. Skasyrskaya, M. Slezak, A. Spalek, M. Steidl, N. Steinbrink, M. Sturm, M. Suesser, H. H. Telle, T. Thümmler, N. Titov, I. Tkachev, N. Trost, A. Unru, K. Valerius, D. Venos, R. Vianden, S. Vöcking, B. L. Wall, N. Wandkowsky, M. Weber, C. Weinheimer, C. Weiss, S. Welte, J. Wendel, K. L. Wierman, J. F. Wilkerson, D. Winzen, J. Wolf, S. Wüstling, M. Zacher, S. Zadoroghny, M. Zboril

The KATRIN experiment will probe the neutrino mass by measuring the beta-electron energy spectrum near the endpoint of tritium beta-decay. An integral energy analysis will be performed by an electro-static spectrometer (Main Spectrometer), an ultra-high vacuum vessel with a length of 23.2 m, a volume of 1240 m^3, and a complex inner electrode system with about 120000 individual parts. Read More

2016Feb
Affiliations: 1The Majorana Collaboration, 2The Majorana Collaboration, 3The Majorana Collaboration, 4The Majorana Collaboration, 5The Majorana Collaboration, 6The Majorana Collaboration, 7The Majorana Collaboration, 8The Majorana Collaboration, 9The Majorana Collaboration, 10The Majorana Collaboration, 11The Majorana Collaboration, 12The Majorana Collaboration, 13The Majorana Collaboration, 14The Majorana Collaboration, 15The Majorana Collaboration, 16The Majorana Collaboration, 17The Majorana Collaboration, 18The Majorana Collaboration, 19The Majorana Collaboration, 20The Majorana Collaboration, 21The Majorana Collaboration, 22The Majorana Collaboration, 23The Majorana Collaboration, 24The Majorana Collaboration, 25The Majorana Collaboration, 26The Majorana Collaboration, 27The Majorana Collaboration, 28The Majorana Collaboration, 29The Majorana Collaboration, 30The Majorana Collaboration, 31The Majorana Collaboration, 32The Majorana Collaboration, 33The Majorana Collaboration, 34The Majorana Collaboration, 35The Majorana Collaboration, 36The Majorana Collaboration, 37The Majorana Collaboration, 38The Majorana Collaboration, 39The Majorana Collaboration, 40The Majorana Collaboration, 41The Majorana Collaboration, 42The Majorana Collaboration, 43The Majorana Collaboration, 44The Majorana Collaboration, 45The Majorana Collaboration, 46The Majorana Collaboration, 47The Majorana Collaboration, 48The Majorana Collaboration, 49The Majorana Collaboration, 50The Majorana Collaboration, 51The Majorana Collaboration, 52The Majorana Collaboration, 53The Majorana Collaboration, 54The Majorana Collaboration, 55The Majorana Collaboration, 56The Majorana Collaboration, 57The Majorana Collaboration, 58The Majorana Collaboration, 59The Majorana Collaboration, 60The Majorana Collaboration, 61The Majorana Collaboration, 62The Majorana Collaboration, 63The Majorana Collaboration, 64The Majorana Collaboration, 65The Majorana Collaboration, 66The Majorana Collaboration, 67The Majorana Collaboration, 68The Majorana Collaboration, 69The Majorana Collaboration, 70The Majorana Collaboration, 71The Majorana Collaboration, 72The Majorana Collaboration, 73The Majorana Collaboration, 74The Majorana Collaboration

We report the first measurement of the total MUON flux underground at the Davis Campus of the Sanford Underground Research Facility at the 4850 ft level. Measurements were done with the Majorana Demonstrator veto system arranged in two different configurations. The measured total flux is (5. Read More

2016Feb
Authors: R. Adhikari, M. Agostini, N. Anh Ky, T. Araki, M. Archidiacono, M. Bahr, J. Baur, J. Behrens, F. Bezrukov, P. S. Bhupal Dev, D. Borah, A. Boyarsky, A. de Gouvea, C. A. de S. Pires, H. J. de Vega, A. G. Dias, P. Di Bari, Z. Djurcic, K. Dolde, H. Dorrer, M. Durero, O. Dragoun, M. Drewes, G. Drexlin, Ch. E. Düllmann, K. Eberhardt, S. Eliseev, C. Enss, N. W. Evans, A. Faessler, P. Filianin, V. Fischer, A. Fleischmann, J. A. Formaggio, J. Franse, F. M. Fraenkle, C. S. Frenk, G. Fuller, L. Gastaldo, A. Garzilli, C. Giunti, F. Glück, M. C. Goodman, M. C. Gonzalez-Garcia, D. Gorbunov, J. Hamann, V. Hannen, S. Hannestad, S. H. Hansen, C. Hassel, J. Heeck, F. Hofmann, T. Houdy, A. Huber, D. Iakubovskyi, A. Ianni, A. Ibarra, R. Jacobsson, T. Jeltema, J. Jochum, S. Kempf, T. Kieck, M. Korzeczek, V. Kornoukhov, T. Lachenmaier, M. Laine, P. Langacker, T. Lasserre, J. Lesgourgues, D. Lhuillier, Y. F. Li, W. Liao, A. W. Long, M. Maltoni, G. Mangano, N. E. Mavromatos, N. Menci, A. Merle, S. Mertens, A. Mirizzi, B. Monreal, A. Nozik, A. Neronov, V. Niro, Y. Novikov, L. Oberauer, E. Otten, N. Palanque-Delabrouille, M. Pallavicini, V. S. Pantuev, E. Papastergis, S. Parke, S. Pascoli, S. Pastor, A. Patwardhan, A. Pilaftsis, D. C. Radford, P. C. -O. Ranitzsch, O. Rest, D. J. Robinson, P. S. Rodrigues da Silva, O. Ruchayskiy, N. G. Sanchez, M. Sasaki, N. Saviano, A. Schneider, F. Schneider, T. Schwetz, S. Schönert, S. Scholl, F. Shankar, R. Shrock, N. Steinbrink, L. Strigari, F. Suekane, B. Suerfu, R. Takahashi, N. Thi Hong Van, I. Tkachev, M. Totzauer, Y. Tsai, C. G. Tully, K. Valerius, J. W. F. Valle, D. Venos, M. Viel, M. Vivier, M. Y. Wang, C. Weinheimer, K. Wendt, L. Winslow, J. Wolf, M. Wurm, Z. Xing, S. Zhou, K. Zuber

We present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved - cosmology, astrophysics, nuclear, and particle physics - in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. Here, we first review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. Read More

We study the number of clusters per site $n(p)$ in lattice percolation on several systems by high-order series analysis, Monte-Carlo simulation on large systems, exact enumerations on small systems, and analysis using results from conformal theory and general percolation theory. We find many new results, including a precise value $0.017625277368(2)$ for $n(p_c)$ for site percolation on the triangular lattice, precise measurement of the amplitude of the singularity $|p-p_c|^{2-\alpha}$, and metric scale factors. Read More

The MAJORANA collaboration is constructing the MAJORANA DEMONSTATOR at the Sanford Underground Research Facility at the Homestake gold mine, in Lead, SD. The apparatus will use Ge detectors, enriched in isotope \nuc{76}{Ge}, to demonstrate the feasibility of a large-scale Ge detector experiment to search for neutrinoless double beta decay. The long half-life of this postulated process requires that the apparatus be extremely low in radioactive isotopes whose decays may produce backgrounds to the search. Read More

Binary sequences with minimal autocorrelations have applications in communication engineering, mathematics and computer science. In statistical physics they appear as groundstates of the Bernasconi model. Finding these sequences is a notoriously hard problem, that so far can be solved only by exhaustive search. Read More

Neutrinoless double beta decay searches play a major role in determining neutrino properties, in particular the Majorana or Dirac nature of the neutrino and the absolute scale of the neutrino mass. The consequences of these searches go beyond neutrino physics, with implications for Grand Unification and leptogenesis. The \textsc{Majorana} Collaboration is assembling a low-background array of high purity Germanium (HPGe) detectors to search for neutrinoless double-beta decay in $^{76}$Ge. Read More

The MAJORANA Collaboration is constructing the MAJORANA DEMONSTRATOR, an ultra-low background, modular, HPGe detector array with a mass of 44-kg (29 kg 76Ge and 15 kg natGe) to search for neutrinoless double beta decay in Ge-76. The next generation of tonne-scale Ge-based neutrinoless double beta decay searches will probe the neutrino mass scale in the inverted-hierarchy region. The MAJORANA DEMONSTRATOR is envisioned to demonstrate a path forward to achieve a background rate at or below 1 count/tonne/year in the 4 keV region of interest around the Q-value of 2039 keV. Read More

The MAJORANA Collaboration will seek neutrinoless double beta decay (0nbb) in 76Ge using isotopically enriched p-type point contact (PPC) high purity Germanium (HPGe) detectors. A tonne-scale array of HPGe detectors would require background levels below 1 count/ROI-tonne-year in the 4 keV region of interest (ROI) around the 2039 keV Q-value of the decay. In order to demonstrate the feasibility of such an experiment, the MAJORANA DEMONSTRATOR, a 40 kg HPGe detector array, is being constructed with a background goal of <3 counts/ROI-tonne-year, which is expected to scale down to <1 count/ROI-tonne-year for a tonne-scale experiment. Read More

The MAJORANA Collaboration is constructing the MAJORANA DEMONSTRATOR, an ultra-low background, 40-kg modular HPGe detector array to search for neutrinoless double beta decay in 76Ge. In view of the next generation of tonne-scale Ge-based 0nbb-decay searches that will probe the neutrino mass scale in the inverted-hierarchy region, a major goal of the MAJORANA 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 background rejection techniques to be applied to the data include cuts based on data reduction, pulse shape analysis, event coincidences, and time correlations. Read More

Let $p_n$ denote the probability that a random instance of the stable roommates problem of size $n$ admits a solution. We derive an explicit formula for $p_n$ and compute exact values of $p_n$ for $n\leq 12$. Read More

The MAJORANA DEMONSTRATOR is a planned 40 kg array of Germanium detectors intended to demonstrate the feasibility of constructing a tonne-scale experiment that will seek neutrinoless double beta decay ($0\nu\beta\beta$) in $^{76}\mathrm{Ge}$. Such an experiment would require backgrounds of less than 1 count/tonne-year in the 4 keV region of interest around the 2039 keV Q-value of the $\beta\beta$ decay. Designing low-noise electronics, which must be placed in close proximity to the detectors, presents a challenge to reaching this background target. Read More

The goal of the \textsc{Majorana} \textsc{Demonstrator} project is to search for 0$\nu\beta\beta$ decay in $^{76}\mathrm{Ge}$. Of all candidate isotopes for 0$\nu\beta\beta$, $^{76}\mathrm{Ge}$ has some of the most favorable characteristics. Germanium detectors are a well established technology, and in searches for 0$\nu\beta\beta$, the high purity germanium crystal acts simultaneously as source and detector. Read More

2015Feb
Affiliations: 1Lawrence Berkeley National Laboratory, 2Pacific Northwest National Laboratory, 3University of South Carolina, 4Institute for Theoretical and Experimental Physics, 5Oak Ridge National Laboratory, 6Joint Institute for Nuclear Research, 7Duke University, 8University of South Dakota, 9South Dakota School of Mines and Technology, 10Lawrence Berkeley National Laboratory, 11South Dakota School of Mines and Technology, 12North Carolina State University, 13Center for Experimental Nuclear Physics and Astrophysics and University of Washington, 14Center for Experimental Nuclear Physics and Astrophysics and University of Washington, 15Center for Experimental Nuclear Physics and Astrophysics and University of Washington, 16University of Tennessee, 17Joint Institute for Nuclear Research, 18Osaka University, 19Los Alamos National Laboratory, 20Duke University, 21Pacific Northwest National Laboratory, 22University of North Carolina, 23University of North Carolina, 24Oak Ridge National Laboratory, 25University of North Carolina, 26Los Alamos National Laboratory, 27Oak Ridge National Laboratory, 28Center for Experimental Nuclear Physics and Astrophysics and University of Washington, 29University of South Carolina, 30Joint Institute for Nuclear Research, 31University of Alberta, 32Osaka University, 33Lawrence Berkeley National Laboratory, 34University of North Carolina, 35Pacific Northwest National Laboratory, 36South Dakota School of Mines and Technology, 37University of North Carolina, 38Black Hills State University, 39Tennessee Tech University, 40Joint Institute for Nuclear Research, 41Institute for Theoretical and Experimental Physics, 42Pacific Northwest National Laboratory, 43Osaka University, 44Center for Experimental Nuclear Physics and Astrophysics and University of Washington, 45North Carolina State University, 46Shanghai Jiao Tong University, 47University of North Carolina, 48University of South Dakota, 49University of North Carolina, 50Lawrence Berkeley National Laboratory, 51Center for Experimental Nuclear Physics and Astrophysics and University of Washington, 52University of South Carolina, 53Osaka University, 54Pacific Northwest National Laboratory, 55University of North Carolina, 56Pacific Northwest National Laboratory, 57University of North Carolina, 58North Carolina State University, 59Lawrence Berkeley National Laboratory, 60University of South Dakota, 61Oak Ridge National Laboratory, 62University of North Carolina, 63Los Alamos National Laboratory, 64Center for Experimental Nuclear Physics and Astrophysics and University of Washington, 65Oak Ridge National Laboratory, 66Los Alamos National Laboratory, 67University of North Carolina, 68Osaka University, 69Joint Institute for Nuclear Research, 70University of North Carolina, 71University of South Dakota, 72Pacific Northwest National Laboratory, 73South Dakota School of Mines and Technology, 74University of South Carolina, 75Black Hills State University, 76Joint Institute for Nuclear Research, 77Duke University, 78University of North Carolina, 79Oak Ridge National Laboratory, 80University of Tennessee, 81Lawrence Berkeley National Laboratory, 82University of North Carolina, 83Oak Ridge National Laboratory, 84University of North Carolina, 85University of South Carolina, 86Los Alamos National Laboratory, 87Joint Institute for Nuclear Research, 88North Carolina State University, 89Oak Ridge National Laboratory, 90Institute for Theoretical and Experimental Physics, 91Joint Institute for Nuclear Research

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. Read More

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. Read More

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 $\beta$-decay spectrum. In this paper we show that a wavelet transform is a very powerful shape analysis method to detect this signature. Read More

We investigate the sensitivity of tritium $\beta$-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 $\sin^2\theta \sim 10^{-8}$. Read More

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. Read More

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. Read More

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. Read More

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. Read More

The stable roommates problem with $n$ agents has worst case complexity $O(n^2)$ in time and space. Random instances can be solved faster and with less memory, however. We introduce an algorithm that has average time and space complexity $O(n^\frac{3}{2})$ for random instances. Read More

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. Read More

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. Read More

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. Read More

In this contribution we review the status and perspectives of direct neutrino mass experiments. These experiments investigate the kinematics of $\beta$-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 $\beta$-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). Read More

The KATRIN experiment is designed to determine the absolute neutrino mass scale with a sensitivity of 200 meV (90 % CL) by measuring the electron energy spectrum close to the endpoint of molecular tritium beta decay. Electrons from a high-intensity gaseous tritium source are guided by a strong magnetic field of a few T to the analyzing plane of the main spectrometer where an integral energy analysis takes place in a low field region (B<0.5 mT). Read More

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. Read More

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. Read More

A wide variety of methods have been used to compute percolation thresholds. In lattice percolation, the most powerful of these methods consists of microcanonical simulations using the union-find algorithm to efficiently determine the connected clusters, and (in two dimensions) using exact values from conformal field theory for the probability, at the phase transition, that various kinds of wrapping clusters exist on the torus. We apply this approach to percolation in continuum models, finding overlaps between objects with real-valued positions and orientations. Read More

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. Read More