Neutrino telescopes open a new observational window on the universe. Neutrino interactions in these detectors can give rise to a combination of electromagnetic cascades, hadronic cascades and long range muons. Cerenkov radiation from these products is detected by the neutrino telescope. In this thesis the observational signatures associated with various neutrino-nucleon interaction products are investigated. Cerenkov radiation is emitted at a distinctive angle, about 40o in ice. The maximum number of optical photons that can be produced per unit charged tracklength is calculated to be 562 photons cm−1. The simulation programs Pythia and GEANT are used to study neutrino interactions using ice as the medium. The production of tau from the tau neutrino interaction is considered and it is found that the Cerenkov angle from tau is not distinctive at low energies, due to its lifetime tau decays before travelling an observable distance. The energy required for a tau neutrino to produce a sharp tau Cerenkov signal is on the order of 1 PeV. In a high energy electron neutrino interaction the resulting hadronic cascade contains high energy pions and kaons. These particles decay, often producing muons that are also high energy and therefore long range. Due to the muons travelling faster than the local speed of light in ice, their signal may be received by the detector earlier than the signal resulting from the event that created the muon. This can complicate the reconstruction of electron neutrino events.

IceCube is the largest operating neutrino observatory. An array of photomultiplier tubes deployed throughout a cubic kilometre of the Antarctic ice at the South Pole detect the Cherenkov radiation from neutrino-nucleon interactions. IceCube is capable of detecting neutrinos over a large energy range. The physics manifesto includes dark matter searches, cosmic ray observation, all sky point source searches, and particle physics parameter constraints. Astrophysical neutrinos are expected to originate from hadronic interactions in some of the most energetic regions in the Universe. The detection of high energy astrophysical neutrinos will provide direct information about the astrophysical sources that produced them. This thesis concentrates on the cascade channel for neutrino detection. Two separate studies are performed; a high energy cascade analysis and a parameterisation of the production of muons within hadronic cascades. The experimental data for the cascade analysis was taken by IceCube from April 2008 to May 2009 when the first 40 IceCube strings were deployed and operational. The analysis was designed to isolate the astrophysical neutrino signal from the atmospheric and muon background. Fourteen cascade-like events were observed, on a background of 2.2 ⁺⁰·⁶ ₋₀·₈ atmospheric neutrino events and 7.7 ± 1.0 atmospheric muon events. This gives a 90% confidence level upper limit of ΦlimE²≤ 7.46 × 10⁻⁸ GeVsr⁻¹s⁻¹cm⁻² , assuming an E⁻² spectrum and a neutrino flavour ratio of 1 : 1 : 1, for the energy range 25.12 TeV to 5011.87 TeV. Decay of hadronic particles in cascades produces muons. If the muons are energetic enough they can significantly alter the topology of the cascade and hence the reconstruction of the event in an analysis. The production of high energy muons within hadronic cascades was simulated and parameterised using Pythia and GEANT simulation programs.

Neutrino telescopes open a new observational window on the universe. Neutrino interactions in these detectors can give rise to a combination of electromagnetic cascades, hadronic cascades and long range muons. Cerenkov radiation from these products is detected by the neutrino telescope. In this thesis the observational signatures associated with various neutrino-nucleon interaction products are investigated. Cerenkov radiation is emitted at a distinctive angle, about 40o in ice. The maximum number of optical photons that can be produced per unit charged tracklength is calculated to be 562 photons cm−1. The simulation programs Pythia and GEANT are used to study neutrino interactions using ice as the medium. The production of tau from the tau neutrino interaction is considered and it is found that the Cerenkov angle from tau is not distinctive at low energies, due to its lifetime tau decays before travelling an observable distance. The energy required for a tau neutrino to produce a sharp tau Cerenkov signal is on the order of 1 PeV. In a high energy electron neutrino interaction the resulting hadronic cascade contains high energy pions and kaons. These particles decay, often producing muons that are also high energy and therefore long range. Due to the muons travelling faster than the local speed of light in ice, their signal may be received by the detector earlier than the signal resulting from the event that created the muon. This can complicate the reconstruction of electron neutrino events.

A study into the reconstruction of cascade like events in the IceCube neutrino detector was performed by utilizing in-situ flasher devices. Reconstruction analysis was done with two different flasher settings at each optical module on string 63 at varying depths in the ice. Three different reconstruction algorithms were used to estimate the characteristics of these cascade type events. The characteristics included the estimated vertex position, and the number of photons produced by each flasher. The number of photons produced can be related to the energy for the cascade event via the detailed knowledge of the cascade physics. Results from the analysis show the strengths of using the center of gravity type approaches to estimating the vertex positions of very bright events, and the inability to reconstruct to an accurate position in z which can occur when using more complicated vertex algorithms on the same events. Analysis using the energy reconstruction modules demonstrated the strengths of using methods that take into account the ice properties inside the detector.

Gamma-ray bursts (GRBs) are brief and sudden explosions radiating most of their energy in the soft γ-ray band ( 100 keV). In the context of multimessenger astroparticle physics recent observations of GRBs provide an excellent benchmark for testing theoretical models of high energy emission mechanisms. Acceleration of hadrons in the engine is expected to produce high energy neutrinos and gamma-rays simultaneously via π±/π0 decays, thus reinforcing the motivation for coincident searches in km3 neutrino telescopes. The Waxman-Bachall spectra and the corresponding expected neutrino rates in IceCube are derived here for GRB090510 amd GRB090902B recently detected by the Fermi Large Area Telescope. The implications of the significant detection of deviations from the Band function fit in photon spectra and a model that explains these extra-components in terms of π0-decay photons are presented here and the relevance to neutrino astronomy is shown.

No description available.

Neutrino astronomy has the potential to greatly improve our understanding of the high-energy universe. An unresolved, diffuse, flux of neutrinos is sensitive to the properties of the population of cosmic accelerators in the universe. Data from 2008 and 2009 collected with the IceCube in-ice detector in a 40-string configuration were searched for an all-flavor ultra high-energy diffuse flux of astrophysical neutrinos. Data were divided into three streams based on signal and background event topology. Robustness was prioritized and a good agreement between real and simulated background data was observed. The search was optimized to give a high sensitivity to a neutrino flux with energy spectrum E-2 and energy greater than 1 PeV. The data sample used in the search for signal had a live time of 345.7 days and the estimated background was 1.2 ± 0.5 events. Taking systematic and statistical uncertainties into account, the sensitivity ΦS was estimated at E2 ΦS = 1.15 · 10-8 GeV cm-2 s-1 sr-1 assuming a 1:1:1 ratio between neutrino flavors at Earth. The full data sample was unblinded once the analysis procedure was fixed and approved by the IceCube collaboration. Three events survived the final filter level. The surviving events look like reasonable neutrino candidate events. Assuming a background only hypothesis, the probability of seeing three or more events is 10%. The resulting 90% confidence level upper limit ΦUL is the most strict to date with E2 ΦUL = 2.32 · 10-8 GeV cm-2 s-1 sr-1. The central 90% signal energy interval is 282 TeV to 214 PeV, and signal acceptance is distributed as 32% muon neutrinos, 39% electron neutrinos and 29% tau neutrinos. Several models for a diffuse extragalactic neutrino flux were excluded.

A study into the reconstruction of cascade like events in the IceCube neutrino detector was performed by utilizing in-situ flasher devices. Reconstruction analysis was done with two different flasher settings at each optical module on string 63 at varying depths in the ice. Three different reconstruction algorithms were used to estimate the characteristics of these cascade type events. The characteristics included the estimated vertex position, and the number of photons produced by each flasher. The number of photons produced can be related to the energy for the cascade event via the detailed knowledge of the cascade physics. Results from the analysis show the strengths of using the center of gravity type approaches to estimating the vertex positions of very bright events, and the inability to reconstruct to an accurate position in z which can occur when using more complicated vertex algorithms on the same events. Analysis using the energy reconstruction modules demonstrated the strengths of using methods that take into account the ice properties inside the detector.

Neutrinos are the ideal cosmic messengers, and can be used to explore the most powerful accelerators in the Universe, in particular the mechanisms for producing and accelerating cosmic rays to incredible energies. By studying clustering of neutrino candidate events in the IceCube detector we can discover sites of hadronic acceleration. We present results on searches for point-like sources of astrophysical neutrinos located in the Southern hemisphere, at energies between 100 GeV and a few TeV. The data were collected during the first year of the completed 86-string detector, corresponding to a detector livetime of 329 days. The event selection focuses on identifying events starting inside the instrumented volume, utilizing several advanced veto techniques, successfully reducing the large background of atmospheric muons. An unbinned maximum likelihood method is used to search for clustering of neutrino-like events. We perform a search in the full Southern hemisphere and a dedicated search using a catalog of 96 pre-defined known gamma-ray emitting sources seen in ground-based telescopes. No evidence of neutrino emission from point-like sources is found. The hottest spot is located at R.A. 305.2° and Dec. -8.5°, with a post-trial p-value of 88.1%. The most significant source in the a priori list is QSO 2022-077 with a post-trial p-value of 14.8%. In the absence of evidence for a signal, we calculate upper limits on the flux of muon-neutrinos for a range of spectra. For an unbroken E-2 neutrino spectrum, the observed limits are between 2.8 and 9.4×10-10 TeV cm-2 s-1, while for an E-2 neutrino spectrum with an exponential cut-off at 10 TeV, the observed limits are between 0.6 and 3.6×10-9 TeV cm-2 s-1. / IceCube

Die Beobachtung von Neutrino-Oszillationen hat gezeigt, dass Neutrinos eine von Null verschiedene Masse haben. Dieses Phänomen wird nicht durch das Standardmodell der Teilchenphysik beschrieben, aber eine mögliche Erklärung für dieses Dilemma ist die Existenz von schweren neutralen Leptonen in Form von rechtshändigen Neutrinos. Abhängig von ihrer Masse und Kopplung zu den Neutrinos des Standardmodells könnten diese Teilchen auch eine wichtige Rolle bei der Lösung weiterer unerklärter Beobachtungen wie Dunkler Materie und der Baryonenasymmetrie des Universums spielen. Diese Arbeit präsentiert die erste Suche nach schweren neutralen Leptonen mit dem IceCube Neutrino-Observatorium. Das standardmäßige Drei-Flavor-Neutrino-Modell wird erweitert, indem ein vierter Massenzustand im GeV-Bereich hinzugefügt wird und eine Mischung mit dem Tau-Neutrino durch den Parameter \ut4 erlaubt wird. Es werden drei Massenwerte für schwere neutrale Leptonen, $m_4$, von \SI{0.3}{\gev}, \SI{0.6}{\gev} und \SI{1.0}{\gev} getestet, wobei zehn Jahre Daten aus den Jahren 2011 bis 2021 verwendet werden. Für keine der drei getesteten Massen wird ein signifikantes Signal von schweren neutralen Leptonen gemessen. Die resultierenden Einschränkungen für den Mischungsparameter sind \ut4$ < 0.19\;(m_4 = \SI{0.3}{\gev})$, \ut4$ < 0.36\;(m_4 = \SI{0.6}{\gev})$ und \ut4$ < 0.40\;(m_4 = \SI{1.0}{\gev})$ im \SI{90}{\percent} - Konfidenzniveau. Diese erste Analyse legt die grundlegende Basis für zukünftige Suchen nach schweren neutralen Leptonen in IceCube. / The observation of neutrino oscillations has established that neutrinos have non-zero masses. This phenomenon is not explained by the standard model of particle physics, but one viable explanation to this dilemma is the existence of heavy neutral leptons in the form of right-handed neutrinos. Depending on their mass and coupling to standard model neutrinos, these particles could also play an important role in solving additional unexplained observations such as dark matter and the baryon asymmetry of the universe. This work presents the first search for heavy neutral leptons with the IceCube Neutrino Observatory. The standard three flavor neutrino model is extended by adding a fourth GeV-scale mass state and allowing mixing with the tau neutrino through the parameter \ut4. Three heavy neutral lepton mass values, $m_4$, of \SI{0.3}{\gev}, \SI{0.6}{\gev}, and \SI{1.0}{\gev} are tested using ten years of data, collected between 2011 and 2021. No significant signal of heavy neutral leptons is observed for any of the tested masses. The resulting constraints for the mixing parameter are \ut4$ < 0.19\;(m_4 = \SI{0.3}{\gev})$, \ut4$ < 0.36\;(m_4 = \SI{0.6}{\gev})$, and \ut4$ < 0.40\;(m_4 = \SI{1.0}{\gev})$ at \SI{90}{\percent} confidence level. This first analysis lays the fundamental groundwork for future searches for heavy neutral leptons in IceCube.