As the IceCube Neutrino Observatory seeks to expand its sensitivity to high PeV-EeV energies by means of the radio technique, the need for fast, efficient and reliable reconstruction methods to recover neutrino properties from radio detector data has emerged. The first recorded investigation into the possibilities of using a neural network based approach to flavor reconstruction is presented. More specifically, a deep convolutional neural network was built and optimized for the purpose of differentiating νe charged current (CC) interaction events from events of all other flavors and interaction modes. The approach is found to be largely successful for neutrino energies above 1018 eV, with a reported accuracy on νe - CC events of > 75% for neutrino energies > 1018.5 eV while maintaining a >60% accuracy for energies > 1018. Predictive accuracy on non- νe - CC events varies between 80% and 90% across the considered neutrino energy range 1017<Eν<1019. The dependence of the accuracy on νe - CC events on neutrino energy is pronounced and attributed to the LPM effect, which alters the features of the radio signals significantly at energies above 1018 eV in contrast to non- νe - CC events. The method shows promise as a first neural network based neutrino flavor reconstruction method, and results can likely be improved through further optimization.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19219号 / 理博第4111号 / 新制||理||1592(附属図書館) / 32218 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 中家 剛, 教授 谷森 達, 准教授 市川 温子 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

No description available.

In this report, we aim to assess the sensitivity and 5$\sigma$ discovery potential of IceCube, the largest neutrino observatory on Earth, and compare it with prior findings. Our thesis will focus on a point source analysis, exploring the energy and declination dependencies, with particular emphasis on high-energy neutrinos. The primary objective is to establish the feasibility of detecting 5$\sigma$ evidence supporting the hypothesis that blazars serve as sources of neutrinos in the Southern sky, as suggested in a recent publication. Our findings indicate a substantial improvement in both discovery potential and sensitivity for the Southern sky in recent years. Furthermore, we highlight the increasing significance of investigating the origins of high-energy neutrinos in the Southern sky.

Nach der Entdeckung eines diffusen Flusses hochenergetischer astrophysikalischer Neutrinos durch das IceCube South Pole Neutrino Observatory im Jahr 2013 sind die Quellen, die für den Großteil dieser Emission verantwortlich sind, immer noch unbekannt. Blazare, jene AGN mit einem relativistischen Jet, der auf die Erde zeigt, gelten als Hauptkandidaten für die Beschleunigung der kosmischen Strahlung und die Produktion hochenergetischer Neutrinos. Diese Doktorarbeit ist motiviert durch den Nachweis des Gammastrahlen-Blazers TXS 0506+056 in räumlicher Koinzidenz mit dem Neutrino IceCube-170922A. 
In dieser Arbeit präsentiere ich die Ergebnisse einer detaillierten Gammastrahlenanalyse des Blazars TXS 0506+056 über 9,6 Jahre Fermi-LAT-Beobachtungen. Die Quelle ist stark variabel im Gammastrahlenband zur Ankunftszeit des Neutrinos IceCube-170922A, was auf eine Neutrino-Gammastrahlen-Verbindung hindeutet. Die Quelle wird jedoch während eines zusätzlichen niederenergetischen Neutrinosignals, das 2014/15 von Ice-Cube in Archivdaten von derselben Quelle entdeckt wurde, in einem niedrigen Zustand beobachtet. In dieser Arbeit wurde ein zweiter Gammastrahlen-Blazar GB6 J1040+0617 in räumlicher und zeitlicher Übereinstimmung mit dem hochenergetischen Neutrino-Ereignis IceCube-141209A gefunden, während er eine erhöhte Aktivität im Gammastrahlen- und im optischen Band zeigt. Eine zweite Suche nach Blazar-Gegenstücken zu hochenergetischen Neutrinos erfolgt durch Echtzeit-Follow-up von mehr als 60 IceCube-Alerts mit dem Fermi-LAT. Der kräftige Blazar PKS 1502+106, der zusammen mit dem Ereignis IceCube-190730A gefunden wurde, stellt einen herausragenden wissenschaftlichen Fall dar. Schließlich wird eine Studie zum Vergleich der durchschnittlichen Gammastrahlenemission der potenziellen Neutrino-Gegenstücke mit der gesamten Stichprobe von Gammastrahlen-Blazaren vorgestellt. Die Ergebnisse zeigen mögliche Hinweise auf eine Korrelation zwischen Neutrino- und Gammastrahlen-Energieflüssen. / After the discovery of a diffuse flux of high-energy astrophysical neutrinos by the IceCube South Pole Neutrino Observatory in 2013, the sources responsible for the majority of this emission are still unknown. Blazars, those AGN with a relativistic jet pointing towards Earth, are considered prime candidates for cosmic-ray acceleration and the production of high-energy neutrinos. This thesis work is motivated by the detection of the flaring gamma-ray blazar TXS 0506+056 in spatial and temporal coincidence with the neutrino event IceCube-170922A, that represented a milestone for the new field of multi-messenger astronomy. In this thesis, I present the results of a detailed gamma-ray analysis of the blazar TXS 0506+056 over 9.6 years of Fermi-LAT observations. The source shows strong flux variability in the gamma-ray band at the arrival of IceCube-170922A, indicating a neutrino gamma-ray connection, while is observed in a lowstate during an additional lower-energy neutrino signal detected from the same source by IceCube in 2014/15 in archival data. This puzzling behaviour has motivated further studies on the blazar sources coincident with single high-energy neutrinos. In this thesis, a second gamma-ray blazar GB6 J1040+0617, is found in spatial and temporal coincidence with the high-energy neutrino event IceCube-141209A while showing enhanced activity in the gamma-ray and optical bands. A second search for blazar counterparts to high-energy neutrinos is done through realtime follow-up of more than 60 IceCube alerts with the Fermi-LAT. The powerful blazar PKS 1502+106 found coincident with the event IceCube-190730A represents an outstanding science case. Lastly, a study to compare the average gamma-ray emission of the potential neutrino counterparts to the entire sample of gamma-ray blazars is presented. The results show possible indications of correlation between neutrino and gamma-ray energy fluxes.

No description available.

The Daya Bay experiment has determined the last unknown mixing angle $theta_{13}$. This thesis describes the layout of the experiment and the detector design. The analysis presented in the thesis covered the water attenuation, spent fuel neutrino and electron anti-neutrino spectrum. Other physics analysis and impact to future experiments are also discussed. / Ph. D.

Nuclear reactors have played an essential role in developing our current understanding of neutrinos. The precision measurement of these high-flux, pure-flavor and controllable artificial neutrino sources shed lights on a wide range of fundamental questions in physics. Specifically, the Reactor Antineutrino Anomaly hints that there may exist a novel eV-scale sterile neutrino, which requires new physics beyond the Standard Model. Performing reactor neutrino spectrum measurements at very-short baseline will improve our imperfect understanding of antineutrino emission from fissile material. CHANDLER is a new-generation neutrino experiment aiming for reactor antineutrino spectrum measurements, to test the eV-scale sterile neutrino oscillation hypothesis unambiguously. The second prototype detector, MiniCHANDLER, was deployed 25 meters from a $2.9~GW_{th}$ commercial nuclear reactor in North Anna, Virginia. To fight against the overwhelming background arising from its surface-level deployment, CHANDLER detectors adopt a novel design using lithium-6 ($^6$Li) loaded zinc sulfide (ZnS) scintillator to tag neutron capture events, which significantly improves the IBD detection efficiency. The use of the Raghavan optical lattice brings enormous enhancement of light collection towards high energy resolution, which unlocks reconstruction of event topology to further suppress backgrounds. The ability of measuring reactor antineutrino spectra enables the potential application of CHANDLER technology in nuclear nonproliferation. This thesis features the prototype detectors instrumentation, data analysis development and Monte Carlo study for the CHANDLER experiment during 2016 to 2020. The detector calibration and energy reconstruction with vertical muon forms a core piece of this thesis. We report our observation of IBD spectrum with 5.5$sigma$ significance with a four month deployment of the minimal shielded MiniCHANDLER prototype at North Anna. The application of separation cuts and topological selections in the analysis are instrumental for a segmented plastic scintillator detector. We also present our results from the proton scintillation quenching measurement at Triangle Universities Nuclear Laboratory, with the deployment of the first prototype detector, MicroCHANDLER, at a neutron beam. / Doctor of Philosophy / The sterile neutrino is a hypothetical particle yet to be observed, whose existence is suggested by a number of physics experiments with strong theoretical motivation. Due to the low chance of a neutrino interacting with matter, most neutrino detectors use a special process called inverse beta decay (IBD) to detect them. The CHANDLER experiment set out to measure antineutrinos produced by a reactor in the vicinity of its core. We found a significant signal of antineutrinos from our four-month deployment. This thesis details the technology and analysis that enables neutrino detection and improves detection efficiency. We also shows how we squeeze out the maximum information available to us from raw data, through the process called reconstruction. Other research topics related to the CHANDLER detector RandD are also included in this thesis.

Over the past 20 years, the detection of neutrino oscillation has reported a lot of important results. The oscillation phenomenon itself has been well proved by various experiments. Some oscillation parameters has been measured and now in the area of precise determination. On the other hand, some new questions like the possibility of the existence of light sterile neutrinos and unexpected 5 MeV bump were raised during the measurement. The Neutrino Lattice Experiment (NuLat) is a detector based on the Raghavan Optical Lattice (ROL). It should be able to offer a compact design of an effective detector with good mobility. It can be extremely useful in the short baseline reactor neutrino oscillation detection community to resolve several confusing issues. In this thesis, we present the calibration results we got from the first active NuLat detector and show what kind of improvements we need for the next version of the NuLat detector based on these results. / Ph. D. / During the last century, physicists have developed a nice framework to describe the physics world we live. The model which we called Standard Model has been constructed to describe the behavior of elementary particles and nicely explain the phenomenon we found from various experiments. However there are still a lot mysteries which cannot be explained by this model and more precise measurements on different fields of particle physics are need to help us improve our understanding about this. Neutrino oscillation is one of the most important field related to this kind of concern. The Neutrino Lattice Experiment (NuLat) is a new type of neutrino detector. It has a good geometry reconstruction ability based on the the Raghavan Optical Lattice (ROL). Since we cannot directly see the elementary particles, we always rely on the signals generated by the reaction between particles and our detector. How to interpret the signals becomes crucial at this point to have high quality experimental data. NuLat is such kind of neutrino detector which offer good ability for us to interpret the signal right. It has a compact design compared to most of other detectors in this field. This is really useful because it can be implemented with limited space where other detectors might have difficulties. Simultaneously the ROL design can help offer nice background rejection ability and high energy resolution. In this thesis, we discuss the progress about develop and assembly of the first active NuLat detector with the preliminary calibration data which give us basic understanding about the performance of this first version.

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.