Neutrinooszillationen sind ein sehr aktives Forschungsfeld. In den letzten Jahrzehnten haben viele Experimente das Phänomen untersucht und sind inzwischen zu Präazisionsmessungen vorangeschritten. Mit seiner Niederenergieerweiterung DeepCore kann das IceCube-Experiment zu diesem Forschungsfeld beitragen. IceCube ist ein 1 km^3 großes Tscherenkow-Neutrino-Teleskop, welches das tiefe, antarktische Eis des Südpols als optisches Medium nutzt. DeepCore ist eine Erweiterung mit dichterer Instrumentierung im unteren Teil des IceCube-Teleskops. Diese dichte Instrumentierung ermöglicht den Nachweis von Neutrinos mit Energien ab einer Energieschwelle von etwa 10 GeV. Jedes Jahr werden Tausende von atmosphärischen Neutrinos oberhalb dieser Schwelle in DeepCore detektiert. Eine Bestimmung der Energie der Neutrinos und des durch sie zurückgelegten Weges durch die Erde ermöglicht die Messung von Neutrinooszillationen. In dieser Arbeit werden zunächst die Möglichkeiten von DeepCore diskutiert, Oszillationen auf unterschiedliche Weise zu messen. Das Verschwinden von Myon-Neutrinos wird als erfolgsversprechender Prozess ausgewählt. Darauf folgt die Beschreibung einer Methode zur Identifizierung von Tscherenkow-Photonen, welche detektiert wurden, bevor sie gestreut wurden -sogenannte- direkte Photonen. Mit Hilfe dieser Photonen kann der Zenitwinkel der Myon-Neutrinos bestimmmt werden. Auch die Energie der Neutrinos wird rekonstruiert. In den Jahren 2011 und 2012 wurden innerhalb von 343 Tagen mit dieser Analyse 1487 Neutrinokandidaten mit Energien zwischen 7 GeV und 100 GeV in DeepCore gefunden. Vergleicht man diese Zahl mit der erwarteten Zahl vom atmosphärischen Neutrinofluss ohne Oszillationen, so ergibt sich ein Defizit von etwa 500 Ereignissen. Die Osziallationsparameter, die die Daten am besten beschreiben, sind im Einklang mit den Parametern, die von anderen Experimenten veröffentlicht wurden. / The study of neutrino oscillations is an active field of research. During the last couple of decades many experiments have measured the effects of oscillations, pushing the field from the discovery stage towards an era of precision and deeper understanding of the phenomenon. The IceCube Neutrino Observatory, with its low energy subarray, DeepCore, has the possibility of contributing to this field. IceCube is a 1 km^3 ice Cherenkov neutrino telescope buried deep in the Antarctic glacier. DeepCore, a region of denser instrumentation in the lower center of IceCube, permits the detection of neutrinos with energies as low as 10 GeV. Every year, thousands of atmospheric neutrinos around these energies leave a strong signature in DeepCore. Due to their energy and the distance they travel before being detected, these neutrinos can be used to measure the phenomenon of oscillations. This work starts with a study of the potential of IceCube DeepCore to measure neutrino oscillations in different channels, from which the disappearance of muon neutrinos is chosen to move forward. It continues by describing a novel method for identifying Cherenkov photons that traveled without being scattered until detected direct photons. These photons are used to reconstruct the incoming zenith angle of muon neutrinos. The total energy of the interacting neutrino is also estimated. In data taken in 343 days during 2011-2012, 1487 neutrino candidates with an energy between 7 GeV and 100 GeV are found inside the DeepCore volume. Compared to the expectation from the atmospheric neutrino flux without oscillations, this corresponds to a deficit of about 500 muon neutrino events. The oscillation parameters that describe the data best are in agreement with the results reported by other experiments. The method and tools presented allow DeepCore to reach comparable precision with the current best results of on-going experiments once five years of data are collected.

Neutrinooszillation, ein Phänomen, das den Neutrino-Flavour nach ihrer Ausbreitung durch den Weltraum verändern kann, ist ein Beweis für nicht-verschwindende Neutrinomassen und ein Hinweis auf eine neue Physik außerhalb des Standardmodells. Diese Arbeit präsentiert die erste Messung zu atmosphärischen Neutrinooszillationen, die sechs Jahre zwischen Mai 2011 und Mai 2017 des IceCube DeepCore Experiment umfasst. Sie erweitert die bisher verfügbare Ereignisauswahl um eine neue Ereignissignatur und einen großeren Energiebereich. Diese Arbeit beschreibt die Methoden, die für die Simulationen der Wechselwirkungen der Neutrinos, die Ereignisauswahl, die Rekonstruktion und die statistische Behandlung von Messdaten und systematischen Messunsicherheiten benutzt werden. Die beste Abschätzung für die Neutrino-Mischungsparameter ist $\Delta m^2_{32} = 2.54^{+0.11}_{-0.12}\cdot 10^{-3}$~eV$^2$ und $\sin^2 \theta_{23} = 0.51\pm0.05$ (68\% C.L.) und gehört zurzeit zu den präzisesten Messungen atmosphärischer Neutrinos. Darüber hinaus wird in dieser Arbeit das Standard-Drei-Flavour-Modell überprüft, indem ein steriles Neutrino mit einer Masse in der Größenordnung von 1 eV eingeführt wird. Die Suche nach Effekten steriler Neutrinos auf atmosphärischen Neutrinooszillationen wird auf drei Jahren Daten, genommen zwischen Mai 2011 und Mai 2014, durchgeführt. Die Ergebnisse stimmen mit dem Standard-Modell der Drei-Neutrino-Oszillation überein, was zu den Obergrenzen für sterilen Neutrino-Mischungsparameter $|U_{\mu4}|^2<0.11$ und $|U_{\tau4}|^2<0.15$ (90\% C.L.) für $\Delta m^2_{41}=1$~eV$^2$ führt. Dieser Ergebnis ist derzeit die stringenste Obergrenze für $|U_{\tau4}|^2$. / Neutrino oscillations, a phenomenon that can change the flavour of neutrinos after their propagation through space, are a proof of non-zero neutrino masses and are an indication of new physics beyond the Standard Model. This work presents the first measurement of the atmospheric neutrino oscillations using six years of IceCube DeepCore data taken between May 2011 and May 2017. It extends the previously available event selection to include new event signatures and to use an extended energy range. This work discusses the techniques used for simulation of neutrino interactions, event selection, reconstruction, and the statistical treatment of data and systematic uncertainties. The best estimates for the neutrino mixing parameters are $\Delta m^2_{32} = 2.54^{+0.11}_{-0.12}\cdot 10^{-3}$~eV$^2$ and $\sin^2 \theta_{23} = 0.51\pm0.05$ (68\% C.L.), which are currently among the most precise measurements obtained with atmospheric neutrinos. In addition, this work tests the standard three-flavour paradigm by introducing one sterile neutrino with a mass on the order of 1~eV. The search for sterile neutrino effects in atmospheric neutrino oscillations is performed with three years of data taken between May 2011 and May 2014. The results are consistent with the standard three-neutrino oscillation picture, leading to limits on the allowed sterile neutrino mixing of $|U_{\mu4}|^2<0.11$ and $|U_{\tau4}|^2<0.15$ (90\% C.L.) for $\Delta m^2_{41}=1$~eV$^2$. Currently, the limit for $|U_{\tau4}|^2$ is the most stringent in the World.

L’expérience Double Chooz a pour but la mesure précise de l’angle de mélange θ₁₃. Son évaluation repose sur l’étude de la disparition des antineutrinos produits par les réacteurs de la centrale de Chooz, disparition due au phénomène d’oscillation des neutrinos. Deux détecteurs identiques composés de liquide scintillant permettent d’effectuer une mesure relative, diminuant ainsi les incertitudes systématiques. Le détecteur proche, qui fournit la normalisation du flux de neutrinos émis, est en cours d’installation, son achèvement est prévu pour le printemps 2014. Le détecteur lointain, sensible à l’effet de θ₁₃, est situé à un kilomètre environ et prend des données depuis 2011. Dans cette première phase de l’expérience, les données acquises par le détecteur lointain sont comparées à une prédiction du flux de neutrinos émis par les réacteurs pour estimer le paramètre θ₁₃. Au sein de cette thèse, l’expérience Double Chooz et son analyse sont présentées. Une attention particulière est portée à l’étude des bruits de fond et au rejet de signaux parasites constitués de flashs lumineux émis par les photo-multiplicateurs. Les flux de neutrons aux interfaces entre les différents volumes du détecteur affectent la définition du volume d’interaction et partant l’efficacité de détection. L’étude détaillée de ces effets de bord est présentée. Dans le cadre de l’expérience Double Chooz, des études ont été menées afin d’améliorer la prédiction des flux de neutrinos émis par les réacteurs. Ces travaux ont mis à jour un déficit des taux de neutrinos observés dans les expériences passées à courtes distances des réacteurs. Ce déficit pourrait s’expliquer par une oscillation vers une saveur stérile. Le projet Stereo a pour but d’observer la distorsion — caractéristique de l’oscillation — du spectre des neutrinos en énergie et en distance de propagation. Cette thèse s’attache à présenter le concept du détecteur, les simulations réalisées, ainsi que les études de sensibilité. Les différents bruits de fond et les blindages envisagés pour s’en prémunir sont enfin discutés. / The Double Chooz experiment aims to measure the θ₁₃ mixing angle through the disappearance—induced by the oscillation phenomenon—of anti-neutrinos produced by the Chooz nuclear reactors. In order to reduce systematic uncertainties, the experiment relies on the relative comparison of detected signals in two identical liquid scintillator detectors. The near one, giving the normalization of the emitted flux, is currently being built and will be delivered in spring 2014. The far detector, sensitive to θ₁₃, is located at about one kilometer and is taking data since 2011. In this first phase of the experiment, the far detector data are compared to a prediction of the emitted neutrino flux to estimate θ₁₃. In this thesis, the Double Chooz experiment and its analysis are presented, especially the background studies and the rejection of parasitic signals due to light emitted by photo-multipliers. Neutron fluxes between the different detector volumes impact the definition of the fiducial volume of neutrino interactions and the efficiency of detection. Detailed studies of these effects are presented. As part of the Double Chooz experiment, studies were performed to improve the prediction of neutrino flux emitted by reactors. This work revealed a deficit of observed neutrino rates in the short baseline experiments of last decades. This deficit could be explained by an oscillation to a sterile state. The Stereo project aims to observe a typical signature of oscillations: the distortion of neutrino spectra both in energy and baseline. This thesis presents the detector concept and simulations as well as sensitivity studies. Background sources and the foreseen shielding are also discussed.

<p>This thesis is devoted to the study of neutrino physics in general and the study of neutrino mixing and oscillations in particular. In the standard model of particle physics, neutrinos are massless, and as a result, they do not mix or oscillate. However, many experimental results now seem to give evidence for neutrino oscillations, and thus, the standard model has to be extended in order to incorporate neutrino masses and mixing among different neutrino flavors.</p><p>When neutrinos propagate through matter, the neutrino mixing, and thus, also the neutrino oscillations, may be significantly altered. While the matter effects may be easily studied in a framework with only two neutrino flavors and constant matter density, we know that there exists (at least) three neutrino flavors and that the matter density of the Universe is far from constant. This thesis includes studies of three-flavor effects and a solution to the two-flavor neutrino oscillation problem in matter with an arbitrary density profile.</p><p>Furthermore, there have historically been attempts to describe the neutrino flavor transitions by other effects than neutrino oscillations. Even if these effects now seem to be disfavored as the leading mechanism, they may still give small corrections to the neutrino oscillation formulas. These effects may lead to erroneous determination of the fundamental neutrino oscillation parameters and are also studied in this thesis in form of damping factors.</p>

<p>In this thesis, two applications of dimensional deconstruction are studied. The first application is a model for neutrino oscillations in the presence of a large decon- structed extra dimension. In the second application, Kaluza{Klein dark matter from a latticized universal extra dimension is studied. The goal of these projects have been twofold. First, to see whether it is possible to reproduce the relevant features of the higher-dimensional continuum theory, and second, to examine the effect of the latticization in experiments. In addition, an introduction to the the- ory of dimensional deconstruction as well as to the theory of continuous extra dimensions is given. Furthermore, the various higher-dimensional models, such as Arkani-Hamed{Dvali{Dimopolous (ADD) models and models with universal extra dimensions, that have been intensively studied in recent years, are discussed.</p>

Double Chooz is a short-baseline experiment, located at the Chooz power plant, designed to observe the neutrino oscillation signal controlled by the θ13 mixing angle. Part of my scientific research, as a graduate student, was directed towards the development of the software needed for the calibration of the Double Chooz Inner Veto and the analysis of the data associated with this task. I was responsible for the quality tests performed in every photomultiplier prior to its installation. I completed all the necessary measurements and analysed the data, extracting the first set of gains and determining the nominal high voltage values needed to be applied in all photomultipliers. All this information served as valuable input to the detector configuration. I was also responsible for the Inner Veto photomultiplier gain analysis during the first months of data taking. I was also very actively involved in data analysis and the estimations of the various sources of background. I initiated a number of methods to isolate and study the cosmic muon events that activate the detector. Additionally I worked on the estimation of the fast neutron rate registered in the detector. The techniques I put forward played a key role and were used in the first Double Chooz publication. Finally, I developed a set of algorithms to identify and reject an instrumental background, relevant for the Double Chooz detector using topological information of the deposited charge.

Double Chooz est une expérience de type «court ligne de base», auprès des réacteurs nucléaires de Chooz, qui a été conçue pour observer les oscillations des neutrinos associées à l’angle de mélange θ13. Une partie de ma recherche était axée sur le développement du logiciel requis pour l'étalonnage de l’Inner Veto de Double Chooz et à l'analyse des données qui y sont associées. J'ai été responsable des tests de qualité effectués sur tous les photomultiplicateurs avant leur installation. J'ai fait toutes les mesures nécessaires et j'ai analysé la majorité des données. Grâce à ce travail, j'ai extrait les premières valeurs des gains et j’ai déterminé les valeurs nominales des hautes tensions nécessaires pour les photomultiplicateurs. Toutes ces données nous ont aidé dans la mise au point du détecteur. Aussi j'ai été le responsable de l'analyse de l’extraction et stabilité des gains pendant l’expérience. J'ai travaillé très activement sur l'analyse des données et en particulier sur l'évaluation des différentes sources de bruit de fond. J'ai développé plusieurs techniques pour isoler et étudier les muons cosmiques qui activent le détecteur Double Chooz. J'ai également travaillé sur l'estimation du taux de neutrons rapides. Les techniques que j'ai présentées ont été utilisées dans la première publication de Double Chooz. Finalement, j'ai étudié un bruit de fond instrumental important pour le détecteur Double Chooz. J'ai développé un nouvel ensemble d'algorithmes pour identifier et rejeter ces événements pathologiques utilisant l'orientation géométrique de la charge à l'intérieur du détecteur. / Double Chooz is a short-baseline experiment, located at the Chooz power plant, designed to observe the neutrino oscillation signal controlled by the θ13 mixing angle. Part of my scientific research, as a graduate student, was directed towards the development of the software needed for the calibration of the Double Chooz Inner Veto and the analysis of the data associated with this task. I was responsible for the quality tests performed in every photomultiplier prior to its installation. I completed all the necessary measurements and analysed the data, extracting the first set of gains and determining the nominal high voltage values needed to be applied in all photomultipliers. All this information served as valuable input to the detector configuration. I was also responsible for the Inner Veto photomultiplier gain analysis during the first months of data taking. I was also very actively involved in data analysis and the estimations of the various sources of background. I initiated a number of methods to isolate and study the cosmic muon events that activate the detector. Additionally I worked on the estimation of the fast neutron rate registered in the detector. The techniques I put forward played a key role and were used in the first Double Chooz publication. Finally, I developed a set of algorithms to identify and reject an instrumental background, relevant for the Double Chooz detector using topological information of the deposited charge.

Le cadre global des oscillations de neutrinos est maintenant bien compris et nous quittons une ère d'exploration pour une ère de précision. L'expérience Double Chooz a pour but de mesurer l'angle de mélange theta13 par l'étude des oscillations des antineutrinos électroniques produits par les réacteurs de la centrale nucléaire de Chooz. Dans cette thèse, une sélection préliminaire des neutrinos détectés dans le détecteur proche est présentée. Les résultats les plus récents de Double Chooz, desquels sont extraits la mesure de theta13 la plus précise que l'expérience peut fournir à ce jour, seront également discutés. La géométrie de l'expérience, relativement simple, représente un avantage considérable afin d'effecteur des études de directionalité des neutrinos dont les résultats, obtenus en analysant les jeux de données les plus récents avec captures sur Gd et H, sont présentés. Ce concept de directionalité peut être appliqué à l'astronomie/astrophysique en offrant la possibilité de localiser des supernovas après détection de leurs neutrinos. Les résultats de simulations de directionalité effectuées avec différentes combinaisons de détecteurs seront présentées. Enfin, plusieurs anomalies pourraient s'expliquer par l'existence de nouveaux états, stériles, de neutrinos. Le but de l¿expérience CeSOX est de confirmer ou réfuter cette hypothèse en déployant une source radioactive à coté d'un grand détecteur comme KamLAND ou Borexino. Dans cette thèse seront présentés les résultats des simulations de signaux et de bruits de fond effectuées afin de valider le principe de l'expérience et de s'assurer de sa sensibilité à l'observation d'une oscillation vers un neutrino stérile. / The framework of neutrino oscillations is quite well-understood and now requires precision rather than exploration. The Double Chooz experiment aims at measuring the theta13 mixing angle through the oscillations of electronic antineutrinos produced by the reactors of the Chooz nuclear power plant. The comparison of the interaction rates and spectral shapes in the two Double Chooz's detectors allows the observation of a disappearance and a spectral distortion, both driven by theta13. In this thesis, a preliminary neutrino selection with the near detector, whose data taking started in December 2014, has been performed. The most recent results of Double Chooz, providing the most precise measurement of the experiment, are presented as well.The simple layout of Double Chooz is a strong advantage to conduct directionality studies. Results of these studies using the most recent neutrino candidates with neutron captures on Gd and H are showed. Neutrino directionality can be applied to astronomy, with the localization of core-collapse supernovae. To this purpose, results of directionality measurements performed with combinations of large neutrino detectors over the globe are presented.Finally, recent anomalies observed in short baseline experiments provided hints of the hypothetical existence of additional sterile neutrino states. The goal of the CeLAND/CeSOX experiment is to test this hypothesis by deploying a radioactive source next to a large liquid scintillator detector such as KamLAND or Borexino. In this thesis, are presented results of signal and background simulations performed to validate the design and assess the sensitivity of such an experiment.

This thesis is devoted to the study of neutrino physics in general and the study of neutrino mixing and oscillations in particular. In the standard model of particle physics, neutrinos are massless, and as a result, they do not mix or oscillate. However, many experimental results now seem to give evidence for neutrino oscillations, and thus, the standard model has to be extended in order to incorporate neutrino masses and mixing among different neutrino flavors. When neutrinos propagate through matter, the neutrino mixing, and thus, also the neutrino oscillations, may be significantly altered. While the matter effects may be easily studied in a framework with only two neutrino flavors and constant matter density, we know that there exists (at least) three neutrino flavors and that the matter density of the Universe is far from constant. This thesis includes studies of three-flavor effects and a solution to the two-flavor neutrino oscillation problem in matter with an arbitrary density profile. Furthermore, there have historically been attempts to describe the neutrino flavor transitions by other effects than neutrino oscillations. Even if these effects now seem to be disfavored as the leading mechanism, they may still give small corrections to the neutrino oscillation formulas. These effects may lead to erroneous determination of the fundamental neutrino oscillation parameters and are also studied in this thesis in form of damping factors. / QC 20101124

[pt] Embora sua detecção seja difícil, neutrinos são considerados como boa ferramenta na astrofísica para obtermos informações das Supernovas, Explosão de Raios Gama e do interior de objetos celestes como o Sol e Núcleos Ativos de Galáxias, porque não é possível explorá-los por meios ópticos. Por interagir muito fracamente com a matéria usual, neutrinos são capazes de percorrer grandes distâncias e atravessar astros e galáxias sem perder energia e, ao serem detectados na Terra, eles trazem informações sobre a fonte emissora, mecanismos de produção destes neutrinos energéticos e, nos permitem estudar as propriedades ainda não completamente conhecidas dos neutrinos, como massas e ângulos de misturas. Um excelente exemplo é o telescópio de neutrinos IceCube que, recentemente, registrou eventos de neutrinos de altas energias, na faixa de TeV e PeV, cujas origens são extragalácticas. Tal pioneirismo abre uma nova janela para estudarmos o Universo. Nessa dissertação, através do fenômeno de oscilação de neutrinos, estudaremos como ocorre a mudança dos sabores leptônicos dos fluxos dos neutrinos de altas energias de origem extragaláctica ao longo de seu caminho, desde a sua criação até a Terra. Analisaremos também o comportamento da razão de sabor dos fluxos de neutrinos em função da fase de violação CP e do ângulo de mistura de sabor leptônico entre segunda e terceira gerações. / [en] Depite that it is difficult to detect neutrinos, they are an interesting tool in astrophysics to obtain information about astronomical objects and events such as the Sun, Supernovae, Active Galactic Nuclei and Gamma Ray Bursts because it is impossible to explore them by optic ways. Due to their very weak interaction with ordinary matter, neutrinos are able to propagate very large distances and pass through stars and galaxies with no energy loss. By detecting neutrinos at Earth, we can get information about neutrino sources as well as the production mechanism and we are also able to study neutrino properties which are not well understood yet, such as mass hierarchy and mixing angles. A great exemple is a neutrino telescope called IceCube which recently recorded, for the first time, high energy neutrino events in the range of TeV and PeV whose source is extragalactic. These events have opened a new window to study the universe. In this dissertation we use neutrino oscillation to study how is the change in the leptonic flavors of high energy neutrino fluxes from their extragalactic sources to the Earth. We also analyse the flavor ratio behavior of neutrino fluxes as a function of CP-violating phase and the mixing angle between second and third generation.