Present status of neutrinoless double beta decay searches

Several new generation experiments searching for neutrinoless double beta decay (0vbb) have become operational over the last five years. This report summarizes the present status of the experimental search and discusses peculiarities, challenges and reached half-life limits/sensitivities in these experiments. So far, no evidence for 0vbb has been found. Starting from the current situation, the paper addresses the question whether an experiment alone will be able to proof unambiguously 0vbb decay and which would be the key-requirements to succeed in this.Comment: Talk at NuPhys2016 conference, Barbican Centre, London, UK, December 12-14, 201

Effect of heat exposure on viability and contractility of cultured prostatic stromal cells

Objectives: Different thermotherapeutic modalities such as transurethral microwave therapy or transurethral needle ablation have been developed to provide effective alternatives to surgical management of benign prostate hyperplasia (BPH). The mechanisms of thermotherapy, however, are not completely understood. We developed a model to investigate the effects of heat application on stromal cell viability and contractility. Methods: Cells isolated from prostatectomy and cystoprostatectomy specimens were cultured in a selective medium. Temperatures ranging from 37 to 50 degrees C were applied for 1 h. Cell contraction was visualized by means of a cell culture microscope equipped with a time-lapse video system. For quantitative analysis, the percentage of contracting cells was evaluated; 10 mu M of phenylepherine were applied for adrenergic stimulation of the eel Is. Results: On immunohistochemistry and phase-contrast microscopy, these cells were identified as prostatic myofibroblasts. Incubation at 50 degrees C for 1 h in vitro induced immediate death of all cells, whereas at 45 degrees C a II cells survived. At 37 degrees C 55% of the cells were seen to contract after addition of phenylephrine. Immediately after incubation at 45 degrees C contraction rate decreased to 29%, but returned to 46% 1 day later. Conclusions: With this model, it is possible to study the mechanisms of thermotherapy in vitro. The results suggest that the effects of thermotherapy are due to the induction of cell death rather than to reduced stromal cell contractility. Furthermore, the data show that treatment is probably only successful if temperatures in excess of 50 degrees C are maintained. Copyright (C) 2000 S. Karger AG, Basel

Identification of radiopure tungsten for low background applications

In this article we explore the availability of radiopure tungsten and itspotential as high density shield material for low background applications. Forcompact shield designs, conventionally, lead is used. Metallic tungsten andtungsten pseudo-alloys reach higher densities up to 19.3 gcm$^{-3}$ and do notexhibit a significant $^{210}$Pb activity, which is a typical intrinsiccontamination in lead. Within several $\gamma$-ray screening campaigns we wereable to identify tungsten samples with activities similar or better than 1mBqkg$^{-1}$ in $^{232}$Th, $^{40}$K, $^{60}$Co and the second part of the$^{238}$U decay chain. In cooperation with a manufacturer we further reduced apersisting contamination in the first part of the $^{238}$U decay chain by afactor of $\sim$2.5 down to (305$\pm$30) mBqkg$^{-1}$. With Monte Carlosimulations, the construction of prototype tungsten-based setups and dedicatedmeasurements, the shield capability of tungsten in comparison to lead wasextensively studied. Specifically, the impact of cosmogenic radiation on thebackground at shallow depth was investigated. We showed that a 6-40% reduction(depending on the exact shield configuration) in the muon-induced neutronfluence is achievable by replacing lead with an equivalent amount of tungstenregarding the suppression of external $\gamma$-radiation. Overall, manybenefits using tungsten especially for low energy applications below a few 100keV are found. The pseudo-tungsten alloy presented in this work paves the wayfor several applications especially regarding background suppression inparticle and astroparticle physics search programs.<br

Low-energy solar neutrino spectroscopy with Borexino : Towards the detection of the solar pep and CNO neutrino flux

Borexino ist ein großvolumiger Detektor, der mit organischem Flüssigszintillator von einer bisher noch nie erreichten geringen Eigenradioaktivität gefüllt ist und für die Echtzeitspektroskopie niederenergetischer Neutrinos konzipiert wurde. Neben dem Hauptziel des Experiments, der Messung des solaren 7Be Neutrinoflusses, wird auch der Nachweis von Sonnenneutrinos aus dem pep-Fusionsprozess und dem CNO-Zyklus angestrebt. Die Nachweisbarkeit dieser Neutrinos hängt von der erfolgreichen Unterdrückung aller relevanten Untergrundkomponenten ab. Die Identifizierung und Reduktion verschiedener Untergrundsignale ist das Hauptthema dieser Dissertation. Im ersten Teil der Arbeit werden myon-induzierte Untergründe analysiert. Der dominierende Untergrund ist das kosmogene Radioisotop 11C, dessen Rate ~10 mal höher ist als die erwartete pep- und CNO-Neutrinorate im bevorzugten Beobachtungsfenster von [0.8,1.3] MeV. Da 11C meistens unter Emission eines Neutrons entsteht, kann 11C über eine Dreifachkoinzidenz (DFK), bestehend aus dem Myon-Signal, dem Neutroneinfang und dem 11C-Zerfall identifiziert werden. Die DFK-Methode und weitere Techniken zur Unterdrückung von 11C wurden optimiert, dadurch wurde eine 11C-Unterdrückungseffizienz von 80% und ein Neutrino-zu-Untergrund-Verhältnis von 1:1.7 erreicht. Dabei geht 61% der Statistik verloren. Der zweite Teil der Arbeit beschäftigt sich mit der Untersuchung des externen Untergrundes. Vorwiegend langreichweitige 2.6 MeV Photonen, die durch 208Tl Zerfälle in den äußeren Detektorkomponenten emittiert werden, können den Szintillator im inneren Bereich des Detektor erreichen. Um die spektrale Form des externen Untergrundes zu bestimmen, wurde eine ~5 MBq 228Th-Quelle eigens angefertigt und damit erstmals eine externe Kalibration durchgeführt. Die gewonnenen Kalibrationsdaten werden zusammen mit den optimierten 11C-Unterdrückungsmethoden den direkten Nachweis solarer pep- und womöglich auch CNO-Neutrinos in Borexino ermöglichen

Highly Sensitive Gamma-Spectrometers of GERDA for Material Screening: Part 2

The previous article about material screening for GERDA points out the importance of strict material screening and selection for radioimpurities as a key to meet the aspired background levels of the GERDA experiment. This is directly done using low-level gamma-spectroscopy. In order to provide sufficient selective power in the mBq/kg range and below, the employed gamma-spectrometers themselves have to meet strict material requirements, and make use of an elaborate shielding system. This article gives an account of the setup of two such spectrometers. Corrado is located in a depth of 15 m w.e. at the MPI-K in Heidelberg (Germany), GeMPI III is situated at the Gran-Sasso underground laboratory at 3500 m w.e. (Italy). The latter one aims at detecting sample activities of the order ~0.01 mBq/kg, which is the current state-of-the-art level. The applied techniques to meet the respective needs are discussed and demonstrated by experimental results.Comment: Featured in: Proceedings of the XIV International Baksan School "Particles and Cosmology" Baksan Valley, Kabardino-Balkaria, Russia, April 16-21,2007. INR RAS, Moscow 2008. ISBN 978-5-94274-055-9, pp. 233-238; (6 pages, 4 figures

Neutron-induced background in the CONUS experiment

CONUS is a novel experiment aiming at detecting elastic neutrino nucleus scattering in the fully coherent regime using high-purity Germanium (Ge) detectors and a reactor as antineutrino ($\bar\nu$) source. The detector setup is installed at the commercial nuclear power plant in Brokdorf, Germany, at a very small distance to the reactor core in order to guarantee a high flux of more than 10$^{13}\bar\nu$/(s$\cdot$cm$^2$). For the experiment, a good understanding of neutron-induced background events is required, as the neutron recoil signals can mimic the predicted neutrino interactions. Especially neutron-induced events correlated with the thermal power generation are troublesome for CONUS. On-site measurements revealed the presence of a thermal power correlated, highly thermalized neutron field with a fluence rate of (745$\pm$30)cm$^{-2}$d$^{-1}$. These neutrons that are produced by nuclear fission inside the reactor core, are reduced by a factor of $\sim$10$^{20}$ on their way to the CONUS shield. With a high-purity Ge detector without shield the $\gamma$-ray background was examined including highly thermal power correlated $^{16}$N decay products as well as $\gamma$-lines from neutron capture. Using the measured neutron spectrum as input, it was shown, with the help of Monte Carlo simulations, that the thermal power correlated field is successfully mitigated by the installed CONUS shield. The reactor-induced background contribution in the region of interest is exceeded by the expected signal by at least one order of magnitude assuming a realistic ionization quenching factor of 0.2.Comment: 28 pages, 28 figure

The Borexino Thermal Monitoring & Management System and simulations of the fluid-dynamics of the Borexino detector under asymmetrical, changing boundary conditions

A comprehensive monitoring system for the thermal environment inside the Borexino neutrino detector was developed and installed in order to reduce uncertainties in determining temperatures throughout the detector. A complementary thermal management system limits undesirable thermal couplings between the environment and Borexino's active sections. This strategy is bringing improved radioactive background conditions to the region of interest for the physics signal thanks to reduced fluid mixing induced in the liquid scintillator. Although fluid-dynamical equilibrium has not yet been fully reached, and thermal fine-tuning is possible, the system has proven extremely effective at stabilizing the detector's thermal conditions while offering precise insights into its mechanisms of internal thermal transport. Furthermore, a Computational Fluid-Dynamics analysis has been performed, based on the empirical measurements provided by the thermal monitoring system, and providing information into present and future thermal trends. A two-dimensional modeling approach was implemented in order to achieve a proper understanding of the thermal and fluid-dynamics in Borexino. It was optimized for different regions and periods of interest, focusing on the most critical effects that were identified as influencing background concentrations. Literature experimental case studies were reproduced to benchmark the method and settings, and a Borexino-specific benchmark was implemented in order to validate the modeling approach for thermal transport. Finally, fully-convective models were applied to understand general and specific fluid motions impacting the detector's Active Volume.Comment: arXiv admin note: substantial text overlap with arXiv:1705.09078, arXiv:1705.0965

Highly sensitive gamma-spectrometers of GERDA for material screening: Part I

The GERDA experiment aims to search for the neutrinoless double beta-decay of 76Ge and possibly for other rare processes. The sensitivity of the first phase is envisioned to be more than one order of magnitude better than in previous neutrinoless double beta-decay experiments. This implies that materials with ultra-low radioactive contamination need to be used for the construction of the detector and its shielding. Therefore the requirements on material screening include high-sensitivity low-background detection techniques and long measurement times. In this article, an overview of material-screening laboratories available to the GERDA collaboration is given, with emphasis on the gamma-spectrometry. Additionally, results of an intercomparison of the evaluation accuracy in these laboratories are presented.Comment: Featured in: Proceedings of the XIV International Baksan School "Particles and Cosmology" Baksan Valley, Kabardino-Balkaria, Russia, April 16-21,2007. INR RAS, Moscow 2008. ISBN 978-5-94274-055-9, pp. 228-232; (5 pages, 0 figures

Statistical Analysis of future Neutrino Mass Experiments including Neutrino-less Double Beta Decay

We perform a statistical analysis with the prospective results of future experiments on neutrino-less double beta decay, direct searches for neutrino mass (KATRIN) and cosmological observations. Realistic errors are used and the nuclear matrix element uncertainty for neutrino-less double beta decay is also taken into account. Three benchmark scenarios are introduced, corresponding to quasi-degenerate, inverse hierarchical neutrinos, and an intermediate case. We investigate to what extend these scenarios can be reconstructed. Furthermore, we check the compatibility of the scenarios with the claimed evidence of neutrino-less double beta decay.Comment: Matches published version: Europhys.Lett.85:51002 (2009). Format changed suitably for ArXi