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

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

Neutrino-less Double Beta Decay and Particle Physics

We review the particle physics aspects of neutrino-less double beta decay. This process can be mediated by light massive Majorana neutrinos (standard interpretation) or by something else (non-standard interpretations). The physics potential of both interpretations is summarized and the consequences of future measurements or improved limits on the half-life of neutrino-less double beta decay are discussed. We try to cover all proposed alternative realizations of the decay, including light sterile neutrinos, supersymmetric or left-right symmetric theories, Majorons, and other exotic possibilities. Ways to distinguish the mechanisms from one another are discussed. Experimental and nuclear physics aspects are also briefly touched, alternative processes to double beta decay are discussed, and an extensive list of references is provided.Comment: 96 pages, 38 figures. Published versio

Modeling of GERDA Phase II data

The GERmanium Detector Array (Gerda) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double-beta (0νββ) decay of 76Ge. The technological challenge of Gerda is to operate in a “background-free” regime in the region of interest (ROI) after analysis cuts for the full 100 kg·yr target exposure of the experiment. A careful modeling and decomposition of the full-range energy spectrum is essential to predict the shape and composition of events in the ROI around Qββ for the 0νββ search, to extract a precise measurement of the half-life of the double-beta decay mode with neutrinos (2νββ) and in order to identify the location of residual impurities. The latter will permit future experiments to build strategies in order to further lower the background and achieve even better sensitivities. In this article the background decomposition prior to analysis cuts is presented for Gerda Phase II. The background model fit yields a flat spectrum in the ROI with a background index (BI) of 16.04+0.78−0.85⋅10−3 cts/(keV·kg·yr) for the enriched BEGe data set and 14.68+0.47−0.52⋅10−3 cts/(keV·kg·yr) for the enriched coaxial data set. These values are similar to the one of Phase I despite a much larger number of detectors and hence radioactive hardware components

Modeling of GERDA Phase II data

The GERmanium Detector Array (GERDA) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double-beta ($0\nu\beta\beta$) decay of $^{76}$Ge. The technological challenge of GERDA is to operate in a "background-free" regime in the region of interest (ROI) after analysis cuts for the full 100$\,$kg$\cdot$yr target exposure of the experiment. A careful modeling and decomposition of the full-range energy spectrum is essential to predict the shape and composition of events in the ROI around $Q_{\beta\beta}$ for the $0\nu\beta\beta$ search, to extract a precise measurement of the half-life of the double-beta decay mode with neutrinos ($2\nu\beta\beta$) and in order to identify the location of residual impurities. The latter will permit future experiments to build strategies in order to further lower the background and achieve even better sensitivities. In this article the background decomposition prior to analysis cuts is presented for GERDA Phase II. The background model fit yields a flat spectrum in the ROI with a background index (BI) of $16.04^{+0.78}_{-0.85} \cdot 10^{-3}\,$cts/(kg$\cdot$keV$\cdot$yr) for the enriched BEGe data set and $14.68^{+0.47}_{-0.52} \cdot 10^{-3}\,$cts/(kg$\cdot$keV$\cdot$yr) for the enriched coaxial data set. These values are similar to the one of Gerda Phase I despite a much larger number of detectors and hence radioactive hardware components

Borexino : geo-neutrino measurement at Gran Sasso, Italy

Geo-neutrinos, electron anti-neutrinos produced in beta-decays of naturally occurring radioactive isotopes in the Earth, are a unique direct probe of our planet's interior. After a brief introduction of the geo-neutrinos' properties and of the main aims of their study, we discuss the features of a detector which has recently provided breakthrough achievements in the field, Borexino, a massive, calorimetric liquid scintillator detector installed at the underground Gran Sasso Laboratory. With its unprecedented radiopurity levels achieved in the core of the detection medium, it is the only experiment in operation able to study in real time solar neutrino interactions in the challenging sub-MeV energy region. Its superior technical properties allowed Borexino also to provide a clean detection of terrestrial neutrinos. Therefore, the description of the characteristics of the detected geo-neutrino signal and of the corresponding geological implications are the main core of the discussion contained in this work

The Status of CONUS

The status of the CONUS coherent reactor neutrino scattering experiment will be presented

Borexino: Geo-neutrino measurement at Gran Sasso, Italy

Geo-neutrinos, electron anti-neutrinos produced in b-decays of naturally occurring radioactive isotopes in the Earth, are a unique direct probe of our planet\u2019s interior. After a brief introduction of the geo-neutrinos\u2019 properties and of the main aims of their study, we discuss the features of a detector which has recently provided breakthrough achievements in the field, Borexino, a massive, calorimetric liquid scintillator detector installed at the underground Gran Sasso Laboratory. With its unprecedented ra-diopurity levels achieved in the core of the detection medium, it is the only experiment in operation able to study in real time solar neutrino interactions in the challenging sub-MeV energy region. Its superior technical properties allowed Borexino also to provide a clean detection of terrestrial neutrinos. Therefore, the description of the characteristics of the detected geo-neutrino signal and of the corresponding geological implications are the main core of the discussion contained in this work