Unter dem geografischen Südpol liegt das IceCube Neutrino Observatorium. Es nutzt einen Kubikkilometer Gletschereis, um Sekundärteilchen aus Neutrinointerkationen zu detektieren. Der Detektor besteht aus insgesamt 5160 optischen Sensoren, die das Cherenkov Licht der relativistischen, geladenen Teilchen messen. Um die Sensitivität und das Detektionsvermögen zu erhöhen sind Vergrößerungen des Detektors mit neuentwickelten optischen Sensoren geplant. Mindestens einer dieser neuen Sensoren soll den Messbereich aus dem optischen Bereich in den UV Bereich erweitern, wobei eine neu entwickelte wellenlängenschiebende Technologie verwendet wird. Um die Verbesserungen dieser neuen Module zu verstehen, wurde ein Kalibrierungsgerät gebaut, getestet und zweimal bei einer in-situ Messung am geografischen Südpol verwendet. Die Messung wurde in dem offenen SPICEcore borehole durchgeführt. In dem Kalibrierungsgerät waren sowohl Lichtquelle, als auch Detektor verbaut. Um die Eiseigenschaften zu vermessen, wurde Licht in möglichst kurzen Pulsen in das Eis gestrahlt. Der Detektor hat nun die Zeitverteilung gemessen, mit der die Photonen wieder zu dem Detektor zurückgestreut werden. Zur Detektion nutzt das Kalibrierungsgerät die gleiche wellenlängenschiebende Technologie, wie die neuentwickelten optischen Module. Die Messung wurde für Wellenlängen zwischen 245 nm und 400 nm an mehreren Tiefen in einem Bereich, in dem auch IceCube liegt durchgeführt. Diese in-situ Messungen sind der erste erfolgreiche Einsatz der neuen wellenlängenschiebenden Technologie. Mit einem likelihood fit wurde die Messung mit einer Simulation verglichen, welche die Absorption und Streuung der Photonen im Eis als Parameter variiert. Mit dieser Analyse konnte für jede Wellenlänge und Tiefe am besten passende Parameter mit Unsicherheiten, bestehend aus statistischen und systematischen Fehlern gefunden werden. Der größte Einfluss auf die Unsicherheiten ist die schlechte Zeitauflösung des Detektors. Die Ergebnisse legen eine hohe Transparenz im tiefen UV-Bereich nahe und erlauben einen tieferen Einblick in die Streuprozesse im antarktischen Eis. / The IceCube Neutrino Observatory lies under the South Pole. It instruments one cubic kilometer of glacial ice to detect secondary particles originating from neutrino interactions. The detector consists of 5160 optical sensors, which measure the Cherenkov light of these relativistic, charged particles. In order to increase the sensitivity and detection range, new extensions with newly developed optical sensors are planned. At least one of these new sensors is supposed to expand the detection range from the optical into the UV range, using a new wavelength shifting technology. To understand the improvements of these new modules, the UV calibration device was built, tested, and deployed twice in in-situ measurements at the geographic South Pole. The measurement was carried out in the open SPICEcore borehole. A light source and a detector were included in the design of the UV calibration device. To measure the ice properties, the light was pulsed in the ice as short as possible. The detector measured the timing distribution of the light getting scattered back. For the detection, the wavelength shifting technology developed for the new optical sensors is used. The measurement was carried out with four wavelengths between 245 nm and 400 nm at several depths, some within the IceCube range. These in-situ measurements successfully applied the new wavelength shifting technology for the first time. Using a likelihood fit, the measurements were compared to a simulation, which varied the absorption and scattering coefficients of the photons in the ice as parameters. With this analysis, a best-fitting set of parameters could be found for each wavelength and depth. The uncertainties are very conservative, consisting of statistical and systematic errors. The most significant influence on the uncertainties is caused by the insufficient time resolution of the detection system. The results suggest a high transparency for the deep UV range and provide a deeper insight into the scattering processes of Antarctic ice.

[pt] Em 2013, o IceCube Neutrino Observatory, localizado no Polo Sul, descobriu um fluxo de neutrinos astrofísicos com energias de PeV. Mais tarde, descobriu-se que este fluxo se estendia até pelo menos aproximadamente 10 TeV. Apesar de muitos esforços desde então, determinar as suas fontes permanece sendo um dos maiores desafios na comunidade de astrofísica. Nesta dissertação, investigamos possíveis fontes através de uma abordagem multimensageira bem motivada. Em qualquer mecanismo para a produção de neutrinos cósmicos, obrigatoriamente há produção simultânea de raios gama com energias comparáveis. Ao contrário de neutrinos, que atravessam o Universo ilesos, raios gama de altas energias sofrem interações com fótons de fundo em um processo de degradação de energia conhecido como cascata eletromagnética. Na Terra, eles contituem o fundo extragalático de raios gama difuso (EGB), medido com precisão pelo Fermi Gamma-ray Space Telescope entre GeV–TeV. Realizando uma análise conservativa, quantitativa e multimensageira, encontra-se uma tensão de maior ou aproximadamente 3delta (possivelmente chegando a aproximdamente 5 delta) entre os dados do IceCube e do EGB, apontando para a exitência de uma nova classe de aceleradores cósmicos de alta energia, como, por exemplo, fontes opacas para raios gama. / [en] In 2013, the IceCube Neutrino Observatory, located at the South Pole, discovered a flux of astrophysical neutrinos with PeV energies, later found to extend down to at least approximately 10 TeV. Despite many efforts since then, determining their sources remains one of the most daunting challenges in the astrophysics community. In this dissertation, we investigate possible sources via a well-motivated multimessenger approach. In any production mechanism of cosmic neutrinos, there must also be a simultaneous production of gamma-rays withcomparable energies. Unlike neutrinos, which travel unscathed throughout the Universe, high energy gamma-rays undergo interactions with background photons in an energy-degrading process known as electromagnetic cascade. At the Earth, they constitute the diffuse extragalactic gamma-ray background (EGB), precisely measured by the Fermi Gamma-ray Space Telescope in the GeV–TeV range. By performing a conservative, quantitative, multimessenger analysis, we find greater than a or approximately to 3 delta (possibly as large as approximately 5 delta) tension between IceCube and EGB data, pointing towards the existence of a new class of high energy cosmic accelerators, such as gamma-ray-opaque sources.

Identifying what makes up the Dark Matter is a long-standing problem to which the abundance of gravitational and cosmological evidence fails to answer. Indirect detection techniques have the aim to unveil the nature of Dark Matter by catching and identifying the products of potential decays and/or annihilations. The work exposed in this thesis is in line with this strategy and has for common thread the quest for line(-like) features in the extraterrestrial fluxes of gamma-rays and neutrinos. The motivation behind this specific interest is that, due to the absence of astrophysical counterparts beyond the GeV scale, these features constitute the ultimate probes (also called “smoking guns”) of the existence of Dark Matter.The thesis is organized in three Parts, the first of which is an introduction to the different facets of the Dark Matter conundrum and why it is not a trivial issue. The works involving gamma-ray line considerations are gathered in Part II, and those exclusively focusing on neutrino lines in Part III.Part II focuses on the effective field theory of Dark Matter decay, first in the context of millicharged particles decaying to gamma-ray lines, and then in the context of (neutral and millicharged) Dark Matter decays involving the simultaneous emission of gamma-ray and neutrino lines. In both cases, the simultaneous emission of cosmic rays is unavoidable and the decays are constrained in a multi-messenger fashion. The complementarity of the results obtained is used to derive model-independent constraints on the Dark Matter lifetime, and shows the possibility to exclude or distinguishsome specific scenarios on the basis of an explicit experimental conjecture.After an introduction to the neutrino detection principles and to the operation of the IceCube detector, Part III focuses on two careful searches for spectral features in the neutrino spectrum. The main goal behind these analyses, conducted in two different regions of the energy spectrum but using the same likelihood ratio procedure, is to popularize dedicated energy distribution studies by showing their ability to reach sensitivity levels comparable to—sometimes even going beyond—those obtained with angular distribution studies or even in the context of gamma-ray line searches. / Option Physique du Doctorat en Sciences / info:eu-repo/semantics/nonPublished

The IceCube Neutrino Observatory is a cubic kilometre scale detector for high-energy neutrinos above hundreds of GeV produced in Earth’s atmosphere as well as outside our solar system whenever particles are accelerated to ultra-relativistic energies. The prompt atmospheric contribution is a result of the creation of heavy mesons with charm components in the atmosphere. Past studies from IceCube using a maximum likelihood estimation over the whole neutrino energy spectrum always reported a best-fit zero prompt contribution so far [1–5], contrary to theory [6, 7]. In this analysis we tried to measure this prompt atmospheric flux in muon neutrino event data from different IceCube releases. In contrast to past studies we performed a binned least-squares fit of the conventional atmospheric flux from data at low energies and subtracted this fit and an astrophysical flux reported by IceCube to measure a prompt contribution. Due to a lack of statistics and accessible information from data releases, our results are also compatible with a zero prompt contribution.

Since the construction of the IceCube Neutrino Observatory was completed in 2010, many amazing discoveries have been made in the field of neutrino physics. Recently a neutrino event has been linked to an blazar-type active galactic nucleus source, bringing us one step closer to understanding the production of high-energy extragalactic neutrinos and ushering in a new era of multimessenger astronomy. This was found by linking the neutrino event to one of the Fermi Collaboration’s gamma ray sources which had a blazar counterpart. The quest to link other neutrino events to AGN (active galactic nuclei) sources through collaboration with the Fermi Large Area Telescope has turned up some interesting candidates. The fact that some of these potential sources are not blazars is curious and, although unconfirmed as neutrino sources, these objects merit further investigation due to their unusual nature.

The IceCube Neutrino Observatory has sensitivity to MeV electron antineutrinos from core-collapse supernovae through an excess of the detection rate over the background. Wavelength-shifting sensors have the potential to greatly increase photon collection making it a promising candidate for improving the measurement of the supernova neutrino light curve in IceCube-Gen2. For high-energy neutrino reconstruction, the competing effect of increased photon collection and the broader time distribution necessitate detailed simulations to determine the impact. In this thesis, we investigate the sensitivity gain caused by wavelength shifters in a future IceCube-Gen2 detector regarding the detection of faint modulations of the supernova neutrino lightcurve. Furthermore, we lay the groundwork for a future high-energy reconstruction through the implementation and integration of wavelength-shifting sensors into the IceCube simulation framework.

<p>A search for a diffuse flux of cosmic neutrinos with energies in excess of 10¹⁴ eV was performed using two years of AMANDA-II data, collected in 2003 and 2004. A 20% evenly distributed sub-sample of experimental data was used to verify the detector description and the analysis cuts. A very good agreement between this 20% sample and the background simulations was observed. The analysis was optimised for discovery, to a relatively low price in limit setting power. The background estimate for the livetime of the examined 80% sample is 0.035 ± 68% events with an additional 41% systematical uncertainty.</p><p>The total neutrino flux needed for a 5σ discovery to be made with 50% probability was estimated to 3.4 ∙ 10^-7 <i>E</i>^-2 GeV s^-1 sr^-1 cm^-2 equally distributed over the three flavours, taking statistical and systematic uncertainties in the background expectation and the signal efficiency into account. No experimental events survived the final discriminator cut. Hence, no ultra-high energy neutrino candidates were found in the examined sample. A 90% upper limit is placed on the total ultra-high energy neutrino flux at 2.8 ∙ 10^-7 <i>E</i>^-2 GeV s^-1 sr^-1cm^-2, taking both systematical and statistical uncertainties into account. The energy range in which 90% of the simulated <i>E</i>^-2signal is contained is 2.94 ∙ 10¹⁴ eV to 1.54 ∙ 10¹⁸eV (central interval), assuming an equal distribution over the neutrino flavours at the Earth. The final acceptance is distributed as 48% electron neutrinos, 27% muon neutrinos, and 25% tau neutrinos.</p><p>A set of models for the production of neutrinos in active galactic nuclei that predict spectra deviating from <i>E</i>^-2 was excluded.</p>

A search for a diffuse flux of cosmic neutrinos with energies in excess of 1014 eV was performed using two years of AMANDA-II data, collected in 2003 and 2004. A 20% evenly distributed sub-sample of experimental data was used to verify the detector description and the analysis cuts. A very good agreement between this 20% sample and the background simulations was observed. The analysis was optimised for discovery, to a relatively low price in limit setting power. The background estimate for the livetime of the examined 80% sample is 0.035 ± 68% events with an additional 41% systematical uncertainty. The total neutrino flux needed for a 5σ discovery to be made with 50% probability was estimated to 3.4 ∙ 10-7 E-2 GeV s-1 sr-1 cm-2 equally distributed over the three flavours, taking statistical and systematic uncertainties in the background expectation and the signal efficiency into account. No experimental events survived the final discriminator cut. Hence, no ultra-high energy neutrino candidates were found in the examined sample. A 90% upper limit is placed on the total ultra-high energy neutrino flux at 2.8 ∙ 10-7 E-2 GeV s-1 sr-1 cm-2, taking both systematical and statistical uncertainties into account. The energy range in which 90% of the simulated E-2 signal is contained is 2.94 ∙ 1014 eV to 1.54 ∙ 1018 eV (central interval), assuming an equal distribution over the neutrino flavours at the Earth. The final acceptance is distributed as 48% electron neutrinos, 27% muon neutrinos, and 25% tau neutrinos. A set of models for the production of neutrinos in active galactic nuclei that predict spectra deviating from E-2 was excluded.

[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.

Cosmic rays reach Earth from beyond the Milky Way and with energies up to 10^20 eV.The responsible accelerators have to date not been discovered. However, multi-messenger astronomy can shed light on the question, based on the principle that protons and nuclei accelerated in dense and energetic environments would also produce gamma rays and neutrinos. Such environments may be found in "blazars", which are therefore cosmic ray accelerator candidates. Their gamma-ray emission has been observed to increase, sometimes by orders of magnitude, during "flares" as observed in light curves taken by the Large Angle Telescope on the Fermi satellite. When the latter was launched in 2008, the IceCube Neutrino Observatory had also started taking data, detecting the Cherenkov light from high-energy neutrino interactions in the glacier ice under the geographic South Pole. These two experiments have enabled multi-messenger searches for neutrinos in time correlation with the gamma-ray emission from blazars. This work builds on this principle and extends it by "stacking" the signal from multiple blazar flares. Thus, their individually undetectable neutrino emission could still be discoverable. One first analysis focused on the blazar TXS 0506+056, whose flare in 2017 coincided with arrival of the neutrino IceCube-170922A. Extending into a lower energy range than the alert, the search found no additional excess neutrinos associated with the flare. A second analysis used 179 bright and variable blazars. They were divided in two specific blazar classes and weighted relatively to each other, with two weighting schemes motivated physically using the observed gamma-ray luminosity and a third, generic weighting to cover unconsidered scenarios. No significant neutrino excess was found in the unblinded likelihood fits for any of the source catalogues and weighting schemes. Their combined trial-corrected p-value was p=(79.1 +/- 0.3)%. The limits derived from this analysis are also discussed and its relation with other searches considered. Since that was the first "blazar flare stacking", this work also proposes further improvements to the analysis which will help advance the search for cosmic ray accelerators. / Les rayons cosmiques proviennent d'au-delà de la Voie lactée et atteignent la Terre avec des énergies pouvant aller jusqu'à 10^20 eV. Les objets qui accélèrent ces rayons cosmiques n'ont toujours pas été découverts. Toutefois, l'astronomie multimessager peut apporter un élément de réponse à cette question, en supposant que les protons et les noyaux accélérés dans des environnements denses et énergétiques pourraient également produire des rayons gamma et des neutrinos. Les "blazars" sont de possibles candidats pour les accélérateurs de rayons cosmiques. Une augmentation de leurs émissions de rayons gamma, parfois de plusieurs ordres de grandeur, a été observée lors de phénomènes qu'on appelle "éruption", comme le montrent les courbes de lumière prises par le télescope spatial Fermi-LAT. Lorsque ce dernier a été lancé en 2008, l'observatoire de neutrinos IceCube avait également commencé à prendre des données, détectant la lumière Tcherenkov provenant d'interactions de neutrinos à haute énergie dans la glace qui se trouve sous le Pôle Sud géographique. Ces deux expériences ont permis de mener à bien des recherches multi-messagers de neutrinos en corrélation temporelle avec l'émission de rayons gamma des blazars. Ce principe est le point de départ de cette thèse, qui va plus loin en employant la méthode du "stacking", qui consiste à combiner les signaux provenant de plusieurs éruptions de blazars. Ainsi, leurs émissions individuelles de neutrinos, habituellement indétectables, pourraient être découvertes après combinaison. Une première analyse s'est concentrée sur le blazar TXS 0506+056, dont l'éruption en 2017 a coïncidée avec l'arrivée de l'évènement IceCube-170922A. En considérant une gamme d'énergie inférieure à celle de l'alerte 170922-A, pas d’autres neutrino excédentaire n’a été associé à l'éruption. Une deuxième analyse est basée sur 179 blazars lumineux et variables. Ces blazars ont été répartis en deux classes spécifiques, et chacun d'entre eux a reçu un poids relatif. Trois schémas de pondération ont été considérés :les deux premiers étant motivés par des observations, le troisième étant plus générique. Aucun excès significatif de neutrinos n'a été observé après avoir effectué des ajustements par maximum de vraisemblance sur les données non masquées, pour les différents catalogues de sources et schémas de pondération. Leur valeur-p combinée est de p=(79.1 +/- 0.3)%. Les limites dérivées de cette analyse sont discutées ainsi que leur rapport avec les résultats d'autres recherches. Puisqu'il s'agit du premier stacking d'éruptions de blazars, nous suggérons également des améliorations à apporter à l'analyse afin de permettre la poursuivre de la recherche d'accélérateurs de rayons cosmiques. / Kosmische straling afkomstig van buiten de Melkweg bereikt de Aarde met energieën tot wel 10^20 eV. De astrofysische bronnen waarin deze deeltjes worden versneld zijn tot op heden nog niet ontdekt. De multi-boodschapperastronomie kan een nieuw licht werpen op de oorsprong van kosmische straling, aangezien protonen en atoomkernen die worden versneld in een dichte en energetische omgeving ook gammastralen en neutrino’s produceren. „Blazars” zijn mogelijke kandidaat-versnellers. Observaties van blazars, gemaakt met de ruimtetelescoop Fermi-LAT ,tonen aan dat hun gammastraling tijdens zogenaamde „flakkers” toeneemt. Rond de tijd dat deze werd gelanceerd, begon het IceCube Neutrino Observatorium ook gegevens te verzamelen. Deze laatste detecteert hoog-energetische neutrino’s aan de hand van het Cherenkovlicht dat geproduceerd wordt tijdens hun interacties met de ijskap bij de geografische zuidpool. Deze twee experimenten hebben het mogelijk gemaakt om een multibooschapperzoektocht te verrichten naar neutrino’s van blazars die een tijdscorrelatie hebben met diens flakkers van gammastraling. Dit is het uitgangspunt van dit proefschrift, waarbij er ook een zogenaamde „stapelmethode” wordt toegepast. Op deze manier kan de neutrino-emissie van indivuele blazarflakkers, die afzonderlijk te zwak is om te detecteren, gecombineerd worden en mogelijks toch worden ontdekt. Een eerste analyse legt de focus op de blazar TXS 0506+056, waarvan een flakker in 2017 samenviel met de aankomst van het neutrino IceCube 170922-A. In een relatief lager energiebereik wordt er geen surplus aan neutrino’s gevonden gecorreleerd met de flakker. In een tweede analyse maken we gebruik van de stapelmethode om neutrino’s te zoeken afkomstig van 179 heldere en variabale blazars. Deze worden onderverdeeld in twee specifieke klassen en krijgen elks een zeker gewicht in de stapelanalyse. Hiervoor worden twee wegingsschema’s gebruikt die gemotiveerd zijn door de geobserveerde gammastraling, alsook een derde generieke weging. Ook hierwordt er geen significant neutrinosignaal geobserveerd. De gecombineerde p waarde is p=(79.1 +/- 0.3)%. Hieruit worden limieten afgeleid, en worden de verbanden met andere zoekacties besproken. Aangezien dit werk de eerste analyse omvat naar neutrino’s afkomstig van blazarflakkers gebruik makende van een stapelmethode, worden er in dit werk ook verdere verbeteringen van de analyse voorgesteld. Deze zullen als een startpunt dienen voor toekomstige zoektochten naar de nog onbekende bronnen van kosmische straling. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished