No description available.

High-energy neutrinos are capable of carrying information over vast distances, and neutrino telescopes such as AMANDA-II provide the means to probe deep inside the violent and energetic interior of the universe. AMANDA-II is located in the glacial ice at South Pole in Antarctica and is optimised to detect Cherenkov emission from neutrino-induced muon tracks with energies above 100 GeV. Data acquired in 2003 with the AMANDA-II detector were searched for a non-localised flux of neutrinos with energies in excess of 1 PeV. Because of the energy dependence of the neutrino mean free path, the Earth is essentially opaque to neutrinos above PeV energies. Combined with the limited overburden of the AMANDA-II detector (about 1.5 km), this means that a potential ultra-high energy neutrino signal will be concentrated at the horizon. The background for the analysis consists of large bundles of muons produced in atmospheric air showers. Owing to their energy losses, muons cannot penetrate the Earth, and the background will be downwards moving. After applying different selection criteria, one event was observed in the final data sample, while 0.16±0.04 background events are expected. The corresponding 90% confidence level upper limit is 4.3. The expected number of neutrino signal events for a 10-6 E-2 GeV/(s sr cm2 ) flux assuming a Φ(νe) : Φ(νμ) : Φ(ντ) = 1:1:1 flavour ratio is 4.1±0.2, yielding an upper limit on the all-flavour neutrino flux of E2 Φ90 ≤ 1.1∙10-6 GeV/(s sr cm2 ), including systematics and with the central 90% of the signal found in the energy range 480 TeV - 1.6 EeV.

This thesis presents theoretical work on the propagation of ultra high energy cosmic rays, from their source to Earth. The different energy loss processes, resulting from cosmic ray interactions with the radiation fields, are addressed. The subsequent uncertainties in the energy loss rates and the effect produced on the arriving cosmic ray spectrum are highlighted. The question of the composition of ultra high energy cosmic rays remains unresolved, with the range of possibilities leading to quite different results in both the secondary fluxes of particles produced through cosmic ray energy loss interactions en route, and the arriving cosmic ray spectra at Earth. A large range of nuclear species are considered in this work, spanning the range of physically motivated nuclear types ejected from the cosmic ray source. The treatment of cosmic ray propagation is usually handled through Monte Carlo simulations due to the stochastic nature of some of the particle physics processes relevant. In this work, an analytic treatment for cosmic ray nuclei propagation is developed. The development of this method providing a deeper understanding of the main components relevant to cosmic ray nuclei propagation, and through its application, a clear insight into the contributing particle physics aspects of the Monte Carlo simulation. A flux of secondary neutrinos, produced as a consequence of cosmic ray energy loss through pion production during propagation, is also expected to be observed at Earth. This spectrum, however, is dependent on several loosely constrained factors such as the radiation field in the infrared region and cosmic ray composition. The range of possible neutrino fluxes obtainable with such uncertainties are discussed in this work. High energy cosmic ray interactions with the radiation fields present within the source may also occur, leading to cosmic ray energy loss before the cosmic ray has even managed to escape. The secondary spectra produced are investigated through the consideration of three candidate sources. A relationship between the degree of photo-disintegration in the source region and the neutrino flux produced through p γ interactions is found.

<p>High-energy neutrinos are capable of carrying information over vast distances, and neutrino telescopes such as AMANDA-II provide the means to probe deep inside the violent and energetic interior of the universe. AMANDA-II is located in the glacial ice at South Pole in Antarctica and is optimised to detect Cherenkov emission from neutrino-induced muon tracks with energies above 100 GeV. </p><p>Data acquired in 2003 with the AMANDA-II detector were searched for a non-localised flux of neutrinos with energies in excess of 1 PeV. Because of the energy dependence of the neutrino mean free path, the Earth is essentially opaque to neutrinos above PeV energies. Combined with the limited overburden of the AMANDA-II detector (about 1.5 km), this means that a potential ultra-high energy neutrino signal will be concentrated at the horizon. The background for the analysis consists of large bundles of muons produced in atmospheric air showers. Owing to their energy losses, muons cannot penetrate the Earth, and the background will be downwards moving. </p><p>After applying different selection criteria, one event was observed in the final data sample, while 0.16±0.04 background events are expected. The corresponding 90% confidence level upper limit is 4.3. The expected number of neutrino signal events for a 10^-6 <i>E</i>^-2 GeV/(s sr cm² ) flux assuming a Φ(ν_e) : Φ(ν_μ) : Φ(ν_τ) = 1:1:1 flavour ratio is 4.1±0.2, yielding an upper limit on the all-flavour neutrino flux of <i>E</i>² Φ₉₀ ≤ 1.1∙10^-6 GeV/(s sr cm² ), including systematics and with the central 90% of the signal found in the energy range 480 TeV - 1.6 EeV. </p>

abstract: For this project, the diffuse supernova neutrino background (DSNB) has been calculated based on the recent direct supernova rate measurements and neutrino spectrum from SN1987A. The estimated diffuse electron antineutrino flux is &sim; 0.10 &ndash; 0.59 /cm2/s at 99% confidence level, which is 5 times lower than the Super-Kamiokande 2012 upper limit of 3.0 /cm2/s, above energy threshold of 17.3 MeV. With a Megaton scale water detector, 40 events could be detected above the threshold per year. In addition, the detectability of neutrino bursts from direct black hole forming collapses (failed supernovae) at Megaton detectors is calculated. These neutrino bursts are energetic and with short time duration, &sim; 1s. They could be identified by the time coincidence of N &ge;2 or N &ge;3 events within 1s time window from nearby (4 &ndash; 5 Mpc) failed supernovae. The detection rate of these neutrino bursts could get up to one per decade. This is a realistic way to detect a failed supernova and gives a promising method for studying the physics of direct black hole formation mechanism. Finally, the absorption of ultra high energy (UHE) neutrinos by the cosmic neutrino background, with full inclusion of the effect of the thermal distribution of the background on the resonant annihilation channel, is discussed. Results are applied to serval models of UHE neutrino sources. Suppression effects are strong for sources that extend beyond z &sim; 10. This provides a fascinating probe of the physics of the relic neutrino background in the unexplored redshift interval z &sim; 10 &ndash; 100. Ultimately this research will examine the detectability of DSNB, neutrino bursts from failed supernovae and absorption effects in the neutrino spectrum. / Dissertation/Thesis / Ph.D. Physics 2013

No description available.

No description available.

No description available.

No description available.

L'identification des sources de rayons cosmiques d'ultra-haute énergie (au-delà de 10^18 eV) constituerait une avancée majeure aussi bien dans le domaine de l'astrophysique que dans celui de la physique des particules. La difficulté principale dans la recherche de telles sources réside dans la perte de l'information directionnelle des rayons cosmiques les moins énergétiques. En effet, leur direction est sujette à des déviations d'amplitude inversement proportionnelle à leur énergie à cause des champs magnétiques qu'il traversent lors de leur propagation jusqu'à la Terre. D'autre part, pour des énergies supérieures à 4x10^(19)eV, l'interaction des rayons cosmiques avec le fond diffus cosmologique limite l'horizon de leurs sources à l'Univers proche (200 Mpc ou moins). Cette thèse a été effectuée au sein de l’observatoire Pierre Auger, le plus grand détecteur de rayons cosmiques de haute énergie. Elle est dédiée à l'étude, la sélection, la reconstruction, ainsi qu'à l'analyse des évènements de plus haute énergie. D'autre part, les particules de plus bas numéro atomique sont plus susceptibles de garder leur direction mais la composition des rayons cosmiques est inconnue à de telles énergies. Une méthode de sélection des événements les plus similaires aux protons a été élaborée et développée dans cette thèse pour étudier la possibilité de leur utilisation pour une "astronomie protons" / Identifying the sources of the ultra-high energy cosmic rays (UHECRs, above 10^{18} eV), the most energetic particles known in the universe, would be an important leap forward for both the astrophysics and particle physics knowledge. However, developing a cosmic-ray astronomy is arduous because magnetic fields, that permeate our Galaxy and the extra-Galactic space, deflect cosmic rays that may lose the directional information on their sources. This problem can be reduced by studying the highest energy end of the cosmic ray spectrum. Indeed, magnetic field deflections are inversely proportional to the cosmic ray energy. Moreover, above 4x10^{19} eV, cosmic rays interact with cosmic photon backgrounds, losing energy. This means that the sources of the highest energy cosmic rays observed on Earth can be located only in the nearby universe (200 Mpc or less). The largest detector ever built for detecting cosmic rays at such high energies is the Pierre Auger Observatory, in Argentina. It combines a 3000 km^2 surface array of water Cherenkov detectors with fluorescence telescopes to measure extensive air showers initiated by the UHECRs. This thesis was developed inside the Auger Collaboration and was devoted to study the highest energy events observed by Auger, starting from the selection and reconstruction up to the analysis of their distribution in the sky. Moreover, since the composition at these energies is unknown, we developed a method to select proton-like events, since high Z cosmic rays are too much deflected by magnetic fields to be used for cosmic-ray astronomy.