Dissertations / Theses on the topic 'Astroparticle physic'
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BASILICO, DAVIDE. "FIRST INDICATION OF SOLAR NEUTRINOS FROM THE CNO CYCLE REACTIONS WITH THE BOREXINO EXPERIMENT." Doctoral thesis, Università degli Studi di Milano, 2020. http://hdl.handle.net/2434/709966.
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Solar neutrinos play a unique and irreplaceable role for the comprehension of the mechanisms powering our star. The study of solar neutrino fluxes allows us to definitely prove that the Sun is powered by thermonuclear reactions occurring in its core. Several questions concerning solar neutrinos are still unsolved. In particular, neutrinos emitted in the CNO cycle of reactions are the only undetected piece of the solar fusion puzzle. This cycle is believed to be the main engine of very massive stars, while it is expected to contribute only ~1% to the solar luminosity. Observing neutrinos from the CNO reactions would have a striking importance in astrophysics, providing the first direct confirmation of the existence of this important energy source in the core of the stars. The Borexino detector is an ultrapure liquid scintillator-based detector located at the Laboratori Nazionali del Gran Sasso. Throughout a more than ten-year long data taking, Borexino has achieved outstanding results about solar neutrino physics, measuring all the neutrino fluxes emitted from the pp-chain nuclear reactions.
This thesis is devoted to the CNO solar neutrino search with Borexino: analyzing the latest three years of data-taking (Phase-III) I provide the first direct experimental indication of a signal of CNO neutrinos. I describe the details of the analysis, the CNO neutrino results and their implications in terms of solar physics.
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Birkel, Michael. "Astroparticle physics beyond the standard model." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388826.
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Medinaceli, Villegas Eduardo <1976>. "Astroparticle physics with nuclear track detectors." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/850/1/Tesi_Medinaceli_Eduardo.pdf.
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This thesis is mainly about the search for exotic heavy particles -Intermediate
Mass Magnetic Monopoles, Nuclearites and Q-balls with the SLIM experiment
at the Chacaltaya High Altitude Laboratory (5230 m, Bolivia), establishing
upper limits (90% CL) in the absence of candidates, which are among the best
if not the only one for all three kind of particles. A preliminary study of the
background induced by cosmic neutron in CR39 at the SLIM site, using Monte
Carlo simulations.
The measurement of the elemental abundance of the primary cosmic ray
with the CAKE experiment on board of a stratospherical balloon; the charge
distribution obtained spans in the range 5≤Z≤31.
Both experiments were based on the use of plastic Nuclear Track Detectors,
which records the passage of ionizing particles; by using some chemical reagents
such passage can be make visible at optical microscopes.
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Medinaceli, Villegas Eduardo <1976>. "Astroparticle physics with nuclear track detectors." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/850/.
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This thesis is mainly about the search for exotic heavy particles -Intermediate
Mass Magnetic Monopoles, Nuclearites and Q-balls with the SLIM experiment
at the Chacaltaya High Altitude Laboratory (5230 m, Bolivia), establishing
upper limits (90% CL) in the absence of candidates, which are among the best
if not the only one for all three kind of particles. A preliminary study of the
background induced by cosmic neutron in CR39 at the SLIM site, using Monte
Carlo simulations.
The measurement of the elemental abundance of the primary cosmic ray
with the CAKE experiment on board of a stratospherical balloon; the charge
distribution obtained spans in the range 5≤Z≤31.
Both experiments were based on the use of plastic Nuclear Track Detectors,
which records the passage of ionizing particles; by using some chemical reagents
such passage can be make visible at optical microscopes.
5
Robbins, Glenn. "New Physics at Colliders and in Space." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1149/document.
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La quête de la nouvelle physique est un défi impliquant à la fois la recherche de particules de matière noire dans les halos galactiques, et celle, aux collisonneurs, de particules dont l’existence est prédite par des théories au-delà du Modèle Standard, telles que la supersymétrie. Alors que les contraintes expérimentales sur ces particules s’intensifient, il devient capital de combiner les limites provenant de ces deux volets afin de guider la suite des recherches. Pour ce faire, il est indispensable d’évaluer et de tenir compte correctement des incertitudes astrophysiques, cosmologiques et nucléaires, pourtant souvent ignorées. La première partie de cette thèse est dédiée à l’étude de ces incertitudes et leur impact sur les contraintes obtenues en supersymétrie, ainsi que la complémentarité entre les contraintes des collisionneurs et de matière noire pour la recherche de nouvelle physique. La deuxième partie est consacrée au développement d’outils de calculs pour les détections directe et indirecte de matière noire, conçus afin de prendre correctement en compte les incertitudes astrophysiques et nucléaires, et à leur implémentation dans le code public SuperIso Relic. Enfin la troisième partie du travail concerne l’étude des implications cosmologiques d’une éventuelle découverte de nouvelles particules aux collisionneurs. Nous avons montré qu’il serait possible de tester les hypothèses du modèle cosmologique standard et d’obtenir des informations sur les propriétés de l’Univers primordial à une époque observationnellement inaccessibleThe quest for new physics is a challenging task which involves, on the one hand, the search for dark matter particles from space, and on the other hand, the search at colliders for particles predicted by theories beyond the Standard Model, such as supersymmetry. With the experimental constraints on new particles getting stronger, it becomes crucial to combine the limits from both sectors in order to guide future searches. To this end, it is essential to estimate and take into account correctly the astrophysical, nuclear and cosmological uncertainties, which are most often ignored. The first part of this thesis is dedicated to the study of such uncertainties and to their impact on the constraints applied on supersymmetry. Moreover, we investigate the interplay between the constraints from colliders and dark matter searches in some detail. The second part concerns the development and the implementation in the public code SuperIso Relic of numerical tools for the calculation of direct and indirect dark matter detection constraints which were designed specifically to take correctly into account astrophysical and nuclear uncertainties. Finally, in the third part of this work, we consider the cosmological implications of a hypothetical discovery of new particles at colliders. We show that it would be possible to test the assumptions of the standard cosmological model and to obtain information on the properties of the primordial Universe at an epoch which is beyond observational reach
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Serpico, Pasquale Dario. "High energy astroparticle physics with cosmic rays and neutrinos." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980374863.
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Wiegand, Alexander [Verfasser]. "The inhomogeneous Universe : its average expansion and cosmic variance / Alexander Wiegand. Fakultät für Physik - Cosmology and Astroparticle Physics." Bielefeld : Universitätsbibliothek Bielefeld, Hochschulschriften, 2012. http://d-nb.info/1026077605/34.
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Kernan, Peter John. "Two astroparticle physics problems : solar neutrinos, and primordial 4[superscript]Helium /." The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487846354482934.
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Wildner, Elena. "Accelerators for Physics Experiments : From Diagnostics and Control to Design." Doctoral thesis, Stockholm : Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4739.
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Bardenet, Rémi. "Towards adaptive learning and inference : applications to hyperparameter tuning and astroparticle physics." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112307.
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Les algorithmes d'inférence ou d'optimisation possèdent généralement des hyperparamètres qu'il est nécessaire d'ajuster. Nous nous intéressons ici à l'automatisation de cette étape d'ajustement et considérons différentes méthodes qui y parviennent en apprenant en ligne la structure du problème considéré.La première moitié de cette thèse explore l'ajustement des hyperparamètres en apprentissage artificiel. Après avoir présenté et amélioré le cadre générique de l'optimisation séquentielle à base de modèles (SMBO), nous montrons que SMBO s'applique avec succès à l'ajustement des hyperparamètres de réseaux de neurones profonds. Nous proposons ensuite un algorithme collaboratif d'ajustement qui mime la mémoire qu'ont les humains d'expériences passées avec le même algorithme sur d'autres données.La seconde moitié de cette thèse porte sur les algorithmes MCMC adaptatifs, des algorithmes d'échantillonnage qui explorent des distributions de probabilité souvent complexes en ajustant leurs paramètres internes en ligne. Pour motiver leur étude, nous décrivons d'abord l'observatoire Pierre Auger, une expérience de physique des particules dédiée à l'étude des rayons cosmiques. Nous proposons une première partie du modèle génératif d'Auger et introduisons une procédure d'inférence des paramètres individuels de chaque événement d'Auger qui ne requiert que ce premier modèle. Ensuite, nous remarquons que ce modèle est sujet à un problème connu sous le nom de label switching. Après avoir présenté les solutions existantes, nous proposons AMOR, le premier algorithme MCMC adaptatif doté d'un réétiquetage en ligne qui résout le label switching. Nous présentons une étude empirique et des résultats théoriques de consistance d'AMOR, qui mettent en lumière des liens entre le réétiquetage et la quantification vectorielleInference and optimization algorithms usually have hyperparameters that require to be tuned in order to achieve efficiency. We consider here different approaches to efficiently automatize the hyperparameter tuning step by learning online the structure of the addressed problem. The first half of this thesis is devoted to hyperparameter tuning in machine learning. After presenting and improving the generic sequential model-based optimization (SMBO) framework, we show that SMBO successfully applies to the task of tuning the numerous hyperparameters of deep belief networks. We then propose an algorithm that performs tuning across datasets, mimicking the memory that humans have of past experiments with the same algorithm on different datasets. The second half of this thesis deals with adaptive Markov chain Monte Carlo (MCMC) algorithms, sampling-based algorithms that explore complex probability distributions while self-tuning their internal parameters on the fly. We start by describing the Pierre Auger observatory, a large-scale particle physics experiment dedicated to the observation of atmospheric showers triggered by cosmic rays. The models involved in the analysis of Auger data motivated our study of adaptive MCMC. We derive the first part of the Auger generative model and introduce a procedure to perform inference on shower parameters that requires only this bottom part. Our model inherently suffers from label switching, a common difficulty in MCMC inference, which makes marginal inference useless because of redundant modes of the target distribution. After reviewing existing solutions to label switching, we propose AMOR, the first adaptive MCMC algorithm with online relabeling. We give both an empirical and theoretical study of AMOR, unveiling interesting links between relabeling algorithms and vector quantization
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Grahn, Karl-Johan. "Measurement of Multi-Jet Production in Proton-Proton Collisions at 7 TeV Center-of-Mass Energy and Hadronic Calibration Studies with the ATLAS Detector at CERN." Doctoral thesis, KTH, Partikel- och astropartikelfysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-29111.
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The ATLAS experiment – situated at the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) in Geneva – took its first collsion data in 2010. Physics topics include finding the Higgs boson, heavy quark physics, and looking for extensions of the Standard Model of Particle Physics such as supersymmetry. In this thesis, inclusive multi-jet production has been studied with the ATLAS detector in proton-proton collisions at a center-of-mass energy of 7 TeV, using an integrated luminosity of 17 nb−1. The anti-kt algorithm with distance parameter ℝ = 0.6 is used to identify jets. The inclusive multi-jet cross section is measured, as well as the ratio ofcross sections for inclusive production of n − 1 and n jets for n ≤ 6. The differential cross sections of the first, second, third and fourth leading jets as a function of transverse momentum, and the differential cross section as a function of the scalar sum of the pT of selected jets, HT, for different jet multiplicities are presented. The ratio of the differential cross section as a function of HT for 3-jet and 2-jet events is also measured. The results are compared to expectations based on leading order QCD, which agree with the data. In addition, a new method for calibrating the hadron response of a segmented calorim-ter is developed and successfully applied to 2004 ATLAS combined beam test data. It is based on a principal component analysis of the calorimeter layer energy deposits, exploiting longitudinal shower development information to improve the measured energyresolution. For pion beams with energies between 20 and 180 GeV, the particle energy is reconstructed within 3% and the energy resolution is improved by 11% to 25% comparedto the response at the electromagnetic scale. Multi-mode optical readout cables for the ATLAS liquid argon calorimeters, about one hundred meters in length, were installed between the main ATLAS cavern and the counting room in the USA15 cavern. Patch cables were spliced onto the ribbons and the fiber attenuation was measured. For 1296 fiber pairs in 54 cables, the average attenuation was 0.69 dB. Only five fibers were found to have losses exceeding 4 dB, resulting in a failure rate of less than 2 per mill. In the ATLAS liquid argon barrel presampler, short circuits consisting of small pieces of dust, metal, etc. can be burned away in situ by discharging a capacitor over the high voltage lines. In a burning campaign in November 2006, seventeen existing short circuits were successfully removed. An investigation on how to implement saturation effects in liquid argon due to high ionization densities resulted in the implementation of the effect in the ATLAS Monte Carlo code, improving agreement with beam test data. The timing structure of hadronic showers was investigated using a Geant4 Monte Carlo. The expected behavior as described in the literature was reproduced, with the exception that some sets of physics models gave unphysical gamma energies from nuclear neutron capture.QC 20110125
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Hofverberg, Petter. "Imaging the high energy cosmic ray sky." Licentiate thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3998.
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Kiss, Mózsi. "Pre-Flight Development of the PoGOLite Pathfinder." Doctoral thesis, KTH, Partikel- och astropartikelfysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-31429.
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The Polarized Gamma-ray Observer (PoGOLite) is a balloon-borne instrument that will measure gamma-ray polarization in the energy range 25-80 keV from astronomical sources such as pulsars, accretion discs and jets from active galacticnuclei. The two additional parameters provided by such observations, polarizationangle and degree, will allow these objects to be studied in a new way, providing information about their emission mechanisms and geometries. The instrument measures azimuthal scattering angles of photons within a closepacked array of phoswich detector cells (PDCs) based on coincident detection of Compton scattering and photoelectric absorption. Each PDC comprises three different scintillating components and combines photon detection, active collimation and bottom anticoincidence into one single unit. The three parts are viewed by a photomultiplier tube (PMT) and pulse shape discrimination is used to identify signals from dierent parts. Surrounding the detector array is a segmented side anticoincidence shield (SAS) made of BGO crystals. The detector elements of the instrument (PDCs, SAS units, PMTs) have been characterized, resulting in a placement scheme which details where within the detector array each element should be placed in order to maximize the instrument sensitivity and response uniformity. Suitable operating parameters for flight, suchas threshold settings and PMT voltages, have also been dened. Geant4 Monte Carlo simulations have shown that a polyethylene shield is needed around the detector array in order to sufficiently reduce the background from atmospheric neutrons. To validate these simulations, a simple detector array with four plastic scintillators and three BGO crystals shielded with polyethylene was irradiated with 14 MeV neutrons. Measured results were accurately recreated i nsimulations, demonstrating that the treatment of neutron interactions in Geant4 is reliable. A Pathnder version of the PoGOLite instrument has been constructed and tested with unpolarized and polarized photon beams, and results have been compared with simulations. The Pathnder is being prepared for a maiden flight from northern Sweden in mid-2011. A circumnavigation is foreseen at an altitude of up to 40 km, whereby the instrument travels westwards over Greenland and Canada and returns over Russia after a period of about 20 days. The main observational targets for this flight will be the Crab system and Cygnus X-1.QC 20110315
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Veledar, Omar. "Development of nanosecond range light sources for calibration of astroparticle cherenkov detectors." Thesis, Northumbria University, 2007. http://nrl.northumbria.ac.uk/3826/.
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In this thesis the development of light emitting diodes (LED) is reviewed. The emphasis is put on devices emitting at the blue region of the spectrum. The physical characteristics of these devices are considered. The main interest is based around the ability of blue LEDs to generate nanosecond range optical flashes. The fast pulsing electronic circuits capable of driving the devices are also reviewed. These are complemented by the potentially exploitable techniques that could provide further benefits for required fast optical pulse generation. The simple, compact and inexpensive electronic oscillator for producing nanosecond range pulses is developed. The circuitry is adapted for generation of pulses necessary to switch on and assist with the turn off of blue InGaN based LEDs. The resulting nanosecond range blue optical pulses are suitable for, but not limited to, the calibration of scintillation counters. These devices used in neutrino detection experiments could provide a better understanding of cosmology and particle physics.
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Buchholz, Annika [Verfasser]. "Various Aspects of Astroparticle Physics and the Implications for Dark Matter Searches / Annika Buchholz." Bonn : Universitäts- und Landesbibliothek Bonn, 2020. http://d-nb.info/1218301287/34.
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Lundquist, Johan. "The Anticoincidence System of the PAMELA Satellite Experiment : Design of the data acquisition system and performance studies." Doctoral thesis, KTH, Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-532.
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PAMELA is a satellite-borne cosmic ray experiment. Its primary scientific objective is to study the antiproton and positron components of the cosmic radiation. This will be done with unprecedented statistics over a wide energy range (~10MeV to ~100GeV). The PAMELA experiment consists of a permanent magnetic spectrometer, an electromagnetic calorimeter, a Time-of-Fight system, a neutron detector and a shower tail catcher. An anticoincidence (AC) system surrounds the spectrometer to detect particles which do not pass cleanly through the acceptance of the spectrometer. PAMELA will be mounted on a Russian Earth-observation satellite, and the launch is scheduled for 2006. The anticoincidence system for PAMELA has been developed by KTH, and consists of plastic scintillator detectors with photomultiplier tube read-out. Extensive testing has been performed during the development phase. Results are presented for environmental tests, tests with cosmic-rays and particle beams.
The design of the digital part of the AC electronics has been realised on an FPGA (Field Programmable Gate Array) and a DSP (Digital Signal Processor). It records signals from the 16 AC photomultipliers and from various sensors for over-current and temperature. It also provides functionality for setting the photomultiplier discrimination thresholds, system testing, issuing alarms and communication with the PAMELA main data acquisition system. The design philosophy and functionality needs to be reliable and suitable for use in a space environment.
To evaluate the performance of the AC detectors, a test utilizing cosmic-rays has been performed. The primary aim of the test was to calibrate the individual channels to gain knowledge of suitable discriminator levels for flight. A secondary aim was to estimate the AC detector efficiency. A lower limit of (99.89±0.04)% was obtained. An in-orbit simulation study was performed using protons to estimate trigger rates and investigate the AC system performance in a second level trigger. The average orbital trigger rate was estimated to be (8.4±0.6)Hz, consisting of (2.0±0.2)Hz good triggers and (6.4±0.5)Hz background. Inclusion of the AC system in the trigger condition to reduce background (for the purpose of data handling capacity) leads to losses of good triggers due to backscattering from the calorimeter (90% loss for 300GeV electrons and 25% for 100GeV protons). A method, using the calorimeter, for identifying backscattering events was investigated and found to reduce the loss of good events to below 1% (300GeV electrons) and 5% (100GeVn of 70%.
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Orsi, Silvio. "Studies of cosmic rays with the anticoincidence system of the PAMELA satellite experiment." Doctoral thesis, Stockholm : Fysik, KTH, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4297.
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Burgess, Thomas. "A Search for Solar Neutralino Dark Matter with the AMANDA-II Neutrino Telescope." Doctoral thesis, Stockholm : Physics Department, Stockholm University, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7378.
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Pinat, Elisa. "The IceCube Neutrino Observatory: search for extended sources of neutrinos and preliminary study of a communication protocol for its future upgrade." Doctoral thesis, Universite Libre de Bruxelles, 2017. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/253046.
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English Version: When humans started looking out at a starry night, astronomy was born. Photons emitted by stars travel up to sometimes billions of light years to reach our eyes, and by studying the properties of this photon flux we are able to infer properties of the star itself. Instead of photons, the IceCube Observatory, located at South Pole, aims at detecting neutrinos and hopes to shed some light on the still unsolved mystery of cosmic-ray acceleration and production mechanisms, and on the most energetic phenomena of the Universe. At the time of this writing, IceCube has proven the existence of an astrophysical neutrino flux with a significance exceeding seven sigmas. Nevertheless, the observed astrophysical neutrino flux shows no significant directional clustering nor a clear association with any known source class so far. Also the latest results given by IceCube’s point source analysis show no significant clustering as well. It is therefore important to widen the search to different source topologies to maximize the discovery potential. In the first part of this work we present an extended source analysis with seven years of IceCube data, adding three years of data to the previous published work and implementing a novel likelihood formulation. Since the extensions of any potential sources are not known a priori, five different extensions have been considered, from 1° to 5°. No significant clustering is observed in any of the maps. The ability of IceCube to establish neutrino astronomy by finding neutrino sources is limited by the number of cosmic neutrinos measured. Despite the aforementioned discovery of an astrophysical flux, detailed spectral studies and searches for specific source locations in this signal remain a challenge with the event sample sizes available from the IceCube instrument. Therefore, a considerable expansion of the current detector, IceCube Gen2, is promoted, which includes the instrumentation of a 10 km3 volume, able to deliver substantial increases in the astrophysical neutrino sample for all flavors. Not only the hardware will be upgraded, but many systems will undergo improvements, such as communications and timing infrastructures. A new communication system has been investigated and is presented in the second part of this document. Binary Phase Shift Keying (BPSK), the simplest digital modulation technique, has been studied as possible communication technique for IceCube Gen2.French Version: Quand les humains ont commencé à regarder le ciel étoilé, l’astronomie est née. Les photons émis par les étoiles voyagent parfois des milliards d’années lumière avant d’atteindre nos yeux, et c’est grâce à l’étude de ce flux de photons que l’on peut déduire les propriétés des étoiles mêmes. Au lieu des photons, l’Observatoire IceCube, situé au Pôle Sud, a pour but de détecter des neutrinos :il espère éclairer le mystère encore non résolu de l’accéleration et des mécanismes de production des rayons cosmiques, ainsi que des phénomènes les plus énergétiques de l’Univers. Au moment où ce document a été rédigé, IceCube a démontré l’existence d’un flux de neutrinos astrophysiques avec une signification statistique excédant sept sigmas. Cependant, le flux de neutrinos astrophysiques observé ne montre aucun regroupement directionnel significatif ni une évidence d’association avec aucune source connue à l’heure actuelle. De plus, les derniers résultats fournis par les analyses de sources ponctuelles de la collaboration IceCube ne montrent non plus aucun regroupement. Il est donc important d’étendre ces recherches vers des typologies de sources différentes pour maximiser le potentiel de son découverte. Dans la première partie de ce travail nous présentons une analyse de source étendue basée sur sept années de données d’IceCube, ce qui rajoute trois ans de données au travail précédemment publié tout en mettant en oeuvre une nouvelle formulation de maximum de vraisem- blance. Comme les extensions de sources potentielles ne sont pas connues à priori, cinq extensions différentes ont été considérées, de 1° à 5°. Aucun regroupement significatif n’a été observé sur aucune des cartes. La capacité d’IceCube de consolider l’astronomie neutrino en découvrant des sources de neutrinos est limitée par le nombre de neutrinos cosmiques mesuré. Malgré la découverte susmentionnée d’un flux astrophysique, les études détaillées de spectre ainsi que les recherches de sources spécifiques pour ce type de signal demeurent un défi, à cause de la limitation de taille disponible des échantillons avec l’instrument IceCube. Par conséquent, une expansion considérable du détecteur actuel, IceCube Gen2, est promue :elle inclut l’instrumentation d’un volume de 10 km3, apte à fournir une augmentation importante des échantillons de neutrinos de toutes les saveurs. Non seulement le hardware sera mis à niveau, mais de nombreux autres systèmes subiront des améliorations, comme les infrastructures de communication et de timing. Un nouveau système de communication a été étudié et est présenté dans la deuxième partie de ce document. Le Binary Phase Shift Keying (BPSK), la technique de modulation numérique la plus simple, a été étudiée comme technique potentielle pour IceCube Gen2.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Sivertsson, Sofia. "Dark matter in and around stars." Licentiate thesis, Stockholm : Skolan för teknikvetenskap, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11259.
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Scorza, Silvia. "EDELWEISS-II, direct Dark Matter search experiment : first data analysis and results." Phd thesis, Université Claude Bernard - Lyon I, 2009. http://tel.archives-ouvertes.fr/tel-00561621.
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One of the greatest mysteries of the universe that, for the present, puzzles the mind of most astronomers, cosmologists and physicists is the question: "What makes up our universe?". This is due to how a certain substance named Dark Matter came under speculation. It is believed this enigmatic substance, of type unknown, accounts for almost three-quarters of the cosmos within the universe, could be the answer to several questions raised by the models of the expanding universe astronomers have created, and even decide the fate of the expansion of the universe. There is strong observational evidence for the dominance of non-baryonic Dark Matter (DM) over baryonic matter in the universe. Such evidence comes from many independent observations over different length scales. The most stringent constraint on the abundance of DM comes from the analysis of the Cosmic Microwave Background (CMB) anisotropies. In particular, the WMAP (Wilkinson Microwave Anisotropy Probe) experiment restricts the abundance of matter and the abundance of baryonic matter in good agreement with predictions from Big Bang Nucleosynthesis. It is commonly believed that such a non-baryonic component could consist of new, as yet undiscovered, particles, usually referred to as WIMPs (Weakly Interacting Massive Particles). Some extensions of the standard model (SM) of particle physics predict the existence of particles that would be excellent DM candidates. In particular great attention has been dedicated to candidates arising in supersymmetric theories: the Lightest Supersymmetric Particle (LSP). In the most supersymmetric scenarios, the so-called neutralino seems to be a natural candidate, being stable in theories with conservation of R-parity and having masses and cross sections of typical WIMPs. The EDELWEISS collaboration is a direct dark matter search experiment, aiming to detect directly a WIMP interaction in a target material, high purity germanium crystal working at cryogenic temperatures. It relies in the measurement of nuclear recoils that produce measurable effects in the crystal such ionization and heat. My PhD thesis is organized as follows. The first chapter aims to provide an introduction to the theoretical framework and the scientific motivation for the following work. The nature of DM has been one of the most challenging topics in contemporary physics since the first evidences of its existence had been found in the 1930s. Cosmologists and astrophysicists on one side, together with particle theorists on the other have put a lot of effort into this field: I will briefly account for their achievements and for the experimental strategies which can be set in this scenario. Since this thesis work was carried out within the EDELWEISS-II direct dark matter experiment, I will focus the next chapter on this topic, describing the main features. The second chapter is related to the set-up of the EDELWEISS-II, the current stage of the EDELWEISS experiment necessary after a first phase that achieved the best upper limit on the WIMP elastic scattering on nucleon as a function of WIMP mass in 2004. [....]
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Olivo, Martino. "Neutrino emission from high-energy component gamma-ray bursts." Licentiate thesis, Uppsala universitet, Högenergifysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-132961.
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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.
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Actis, Oxana. "Search for neutrino-induced cascades with 5 years of the AMANDA-II data." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2008. http://dx.doi.org/10.18452/15864.
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Das Antarctic Muon And Neutrino Detector Array (AMANDA) ist ein Cherenkov Detektor, der sich im Gletscher der Antarktis am Südpol befindet. Wir präsentieren die Analyse von Daten, die in den Jahren 2000 bis 2004 gesammelt wurden, die einer effektiven Detektorlaufzeit von 1001 Tagen entsprechen. Die Suche zielt auf den Nachweis von elektomagnetische und hadronische Teilchenschauern, so gennante Kaskaden, die durch Elektron- und Tauneutrinowechselwirkung produziert werden können. Die hadronischen Kaskaden können auch über neutrale Ströme Wechselwirkung von Neutrinos aller Arten produziert werden. Der Kaskadenkanal hat einige Vorteile in der Suche nach einem diffusen Fluss von astrophysikalischen Neutrinos. Durch die gute Energieauflösung des AMANDA Detektors kann man zwischen einem harten astrophysikalische Spektrum und einem weichen atmosphärischen Spektrum unterscheiden. Außerdem ist der atmosphärischen Elektronneutrinos Fluss um eine Gößenordnung kleiner als der atmosphärische Myonneutrinofluss. Der Untergrund von atmosphärischem Myonen aus Luftschauern kann unterdrückt werden, weil diese als Spuren im Detektor erscheinen und leicht zu identifizieren sind. Mit der hohen Untergrundunterdrückung ist es möglich die Analyse über einen Raumwinkel von 4pi für Energien gegen 50 TeV zu erstrecken. Die Anzahl von gefundenen Ereignissen in dieser Analyse stimmt mit der Erwartung von Hintergrundereignissen überein. Deshalb berechnen wir eine obere Grenze für den diffusen Neutrinofluss aller Neutrinoarten, unter der Annahme, dass alle Neutrinoarten im Verhältnis 1:1:1 auftreten. Die obere Grenze für einen Nuetrinofluss im Energiebereich von 40 TeV bis 9 PeV mit einem Spektrum von E-2 ist 3.96x10-7 GeV s-1 sr-1 cm-2 bei einem Konfidenzniveau von 90%. Dies ist momentan die niedrigste Grenze für einen diffusen Neutrinoflüss aller Neutrinoarten.The Antarctic Muon And Neutrino Detector Array (AMANDA) is a Cherenkov detector deployed in the Antarctic ice cap at the South Pole. We present the analysis of the AMANDA data collected during 1001 effective days of the detector lifetime be tween the years 2000 and 2004. We focus our search on electromagnetic and hadronic cascades which are produced in charged-current interactions of high-energy electron or tau neutrinos and in neutral-current interactions of neutrinos of any flavor. There are several advantages associated with the cascade channel in the search for a "diffuse" flux of astrophysical neutrinos. The AMANDA''s energy resolution allows us to distinguish between a hard astrophysical spectrum and a soft atmospheric spectrum. In addition, the flux of atmospheric electron neutrinos is lower than that of atmospheric muon neutrinos by one order of magnitude, and the background from downward-going atmospheric muons can be suppressed due to their track-like topology. The low background in this channel allows us to attain a 4pi acceptance above energies of about 50 TeV. The number of events observed in this analysis is consistent with the background expectations. Therefore, we calculate an upper limit on the diffuse all-flavor neutrino flux assuming a flavor ratio 1:1:1 at the detection site. A flux of neutrinos with a spectrum falling as E-2 is limited to 3.96x10-7 GeV s-1 sr-1 cm-2 at 90% C.L. for a neutrino energy range spanning from 40 TeV to 9 PeV. This upper limit is currently the most sensitive limit on the diffuse all-flavor astrophysical neutrino flux.
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Wu, Juan. "Measurements of Cosmic Ray Antiprotons with PAMELA." Licentiate thesis, KTH, Particle and Astroparticle Physics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12378.
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Johansson, Henrik. "Searching for an Ultra High-Energy Diffuse Flux of Extraterrestrial Neutrinos with IceCube 40." Doctoral thesis, Stockholms universitet, Fysikum, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-57169.
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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.
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Ström, Rickard. "Exploring the Universe Using Neutrinos : A Search for Point Sources in the Southern Hemisphere Using the IceCube Neutrino Observatory." Doctoral thesis, Uppsala universitet, Högenergifysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-265522.
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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
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Marini, Bettolo Cecilia. "Performance Studies and Star Tracking for PoGOLite." Doctoral thesis, KTH, Partikel- och astropartikelfysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-13015.
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PoGOLite is a balloon-borne experiment, which will study polarized soft γ-ray emissionfrom astrophysical targets in the 25-80 keV energy range by applying well-typephoswich detector technology. Polarized γ-rays are expected from a wide variety of sources including rotation-powered pulsars, accreting black holes and neutron stars,and jet-dominated active galaxies. Polarization measurements provide a powerfulprobe of the γ-ray emission mechanism and the distribution of magnetic and radiation fields around the source. The polarization is determined using Compton scattering and photoelectric absorption in an array of 217 plastic scintillators. The sensitive detector is surrounded by a segmented Bismuth Germanium Oxide (BGO) anticoincidence shield. The function of this shield is to reduce backgrounds from charged cosmic rays, primary and atmospheric γ-rays, and atmospheric and instrumenta lneutrons. The anticoincidence shield consists of 427 BGO crystals with three different geometries. The characteristics of the BGO crystals of the bottom anticoincidence shield have been studied with particular focus on the light yield.The maiden flight of PoGOLite will be with a reduced detector volume “pathfinder” instrument. The flight, lasting about 24 hours, is foreseen from Esrange, Sweden in August 2010. The performance of the pathfinder has been studied using computer simulations. The effect of atmospheric attenuation, both on the signal of theastronomical target and on the background, are studied. These allow an observationstrategy to be developed for the forthcoming flight. A polarization analysis method is described and applied to an observation example. The method sets anupper limit on the accuracy with which the polarimeter will be able to detect polarization the angle and degree. The PoGOLite polarimeter has a relatively small field of view (2.4◦×2.4◦) which must be kept aligned to objects of interest on the sky. A star tracker forms part of the attitude control system. The star trackersystem comprises a CCD camera, a lens, and a baffle system. Preliminary studiesof the star identification performance are presented and are found to be compatible with the environment around the Crab, which is the main observational target for the first flight.QC20100629
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Hofverberg, Petter. "A New Measurement of Low Energy Antiprotons In the Cosmic Radiation." Doctoral thesis, Stockholm : Fysik, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9427.
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Hauschildt, Tonio. "Search for cosmic point sources of high energy neutrinos with the AMANDA-II detector." Doctoral thesis, [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973092378.
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Mohrmann, Lars. "Characterizing cosmic neutrino sources." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17377.
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Das IceCube Neutrino Observatorium ist ein km^3-großes Neutrinoteleskop und befindet sich am geographischen Südpol. Das Ziel des Experiments ist es, kosmische Neutrinos nachzuweisen. Es wird erwartet, dass solche Neutrinos in Wechselwirkungen von hochenergetischer kosmischer Strahlung mit Materie oder Photonen in der Nähe ihrer Beschleunigungsumgebung entstehen. Der erste Nachweis für einen Fluss von kosmischen Neutrinos wurde von der IceCube-Kollaboration erbracht. Der Ursprung des Flusses ist noch nicht bekannt, dennoch können die Eigenschaften der Quellen durch eine Messung des Energiespektrums und der Zusammensetzung aus Elektron-, Muon-, und Tau-Neutrinos des Flusses eingeschränkt werden. Die vorliegende Arbeit stellt die erste umfassende Analyse von Daten des IceCube-Experiments im Hinblick auf diese Eigenschaften des Flusses dar. Hierfür wurden mehrere Datensätze kombiniert und gemeinsam analysiert. Es wurden experimentell beobachtete Verteilungen von rekonstruierter Energie, Zenithwinkel und Teilchen-Signatur mit Modellverteilungen angepasst. Unter der Annahme, dass der Fluss isotrop ist und zu gleichen Teilen aus allen Neutrino-Flavors besteht, wird das Spektrum durch ein Potenzgesetz mit Normalisierung (6.7_{-1.2}^{+1.1})x10^{-18}GeV^{-1}s^{-1}sr^{-1}cm^{-2} bei 100 TeV und spektralem Index -2.50+-0.09 zwischen Neutrino-Energien von 25 TeV und 2.8 PeV gut beschrieben. Ein spektraler Index von -2 kann mit einer Signifikanz von 3.8 Standardabweichungen ausgeschlossen werden. Die Flavor-Zusammensetzung ist kompatibel mit Erwartungen für Standard-Prozesse der Neutrino-Produktion. Die ausschließliche Produktion von Elektron-Neutrinos kann hingegen mit einer Signifikanz von 3.6 Standardabweichungen ausgeschlossen werden. Unter der Annahme, dass die Neutrino-Flavor während der Propagation von den Quellen zur Erde durch Standard-Neutrino-Oszillationen transformiert werden, beträgt der gemessene Anteil an Elektron-Neutrinos an der Erde (18+-11)%.The IceCube Neutrino Observatory is a km^3-sized neutrino telescope located at the geographical South Pole. Its primary purpose is the detection of high-energy cosmic neutrinos. Such neutrinos are expected to be produced in interactions of high-energy cosmic rays with ambient matter or photons close to their acceleration sites. The IceCube Collaboration has reported the first evidence for a flux of high-energy cosmic neutrinos. While the origin of the flux remains unknown so far, the properties of its sources can be constrained by measuring its energy spectrum and its composition of electron, muon, and tau neutrinos. The present work constitutes the first comprehensive analysis of IceCube data with respect to these principal characteristics of the flux. Several data sets were assembled and simultaneously studied in a combined analysis. Experimentally observed distributions of reconstructed energy, zenith angle and particle signature were fitted with model distributions. Assuming the cosmic neutrino flux to be isotropic and to consist of equal flavors at Earth, the all-flavor spectrum is well described by a power law with normalization (6.7_{-1.2}^{+1.1})x10^{-18}GeV^{-1}s^{-1}sr^{-1}cm^{-2} at 100 TeV and spectral index -2.50+-0.09 for neutrino energies between 25 TeV and 2.8 PeV. A spectral index of -2 is disfavored with a significance of 3.8 standard deviations. The flavor composition is compatible with that expected for standard neutrino production processes at the sources. However, a scenario in which only electron neutrinos are produced is disfavored with a significance of 3.6 standard deviations. Assuming that standard neutrino oscillations transform the neutrino flavors during propagation from the sources to the Earth, the measured fraction of electron neutrinos at Earth is (18+-11)%.
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Garrigoux, Tania. "Étude des emissions diffuses avec l'expérience H.E.S.S." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066178/document.
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High Energy Stereoscopic System (H.E.S.S.) est un réseau de cinq télescopes à imagerie Cherenkov atmosphérique, localisé dans l’hémisphère sud, ayant pour but principal l’étude de rayons cosmiques couvrant une gamme d’énergie de 30 GeV à plusieurs dizaines de TeV. La technique de détection Cerenkov ainsi que les spécificités de la méthode de reconstruction employée par H.E.S.S. I (première phase de l’expérience H.E.S.S.), sont décrites dans cette thèse. Après plus de dix ans d’activité, l’expérience H.E.S.S. a enregistré une quantité de données importante. En plus des régions d’intérêts sondées par ces détecteurs, où des sources astrophysiques ont déjà été dévoilées, l’étude d’événements collectés permet d’améliorer la compréhension de leur environnement sous-jacent. En effet, des émissions diffuses encore non-comprises se superposent aux rayonnements provenant de sources actives. Elles sont pourtant d’un intérêt significatif en astrophysique, physique des particules, cosmologie et même dans certains domaines de physique au-delà des modèles standards, tel que la recherche de matière noire. Les émissions diffuses et leurs précédentes études sont présentées dans cette thèse, ainsi que leurs possibles origines, depuis les mécanismes d’accélération de rayons cosmiques jusqu’à la production de rayon gamma dans les sources actives ou encore par des processus secondaires impliquant les interactions de rayons cosmiques avec le milieu interstellaire. Dans ce travail, des outils pour étudier les émissions diffuses ont été développés. L’approche choisie permet de distinguer les différentes composantes dans les données étudiées et extraire une estimation de leur poids dans le spectre. Elle prend en compte deux aspects, expliqués séparément dans cette thèse. Dans un premier temps, la morphologie de la source active présente dans le champ de vue est utilisée pour la modéliser et obtenir son spectre. Ensuite, pour distinguer les différentes contributions du fond, la méthode se base sur des fonctions de densité de probabilité construites à partir de variables discriminantes. L’étude et manipulation préliminaires nécessaires des variables discriminantes sont également détaillées. Des sources astrophysiques connues sont utilisées comme référence pour l’analyse. Les spectres résultants pour la source active, les électrons et hadrons diffus sont présentés et discutés, ainsi qu’une limite supérieure sur le flux de l’émission diffuse gamma extragalactique. Les erreurs systématiques associées ont été estimées. Une technique de "unfolding" a été mise en place et utilisée pour vérifier les résultats pour les émissions diffusesThe High Energy Stereoscopic System (H.E.S.S.) is an array of five Imaging Atmospheric \v{C}erenkov Telescopes (IACT) located in the Southern Hemisphere, whose primary goal is the study of cosmic gamma-rays in the 30 GeV - few tens of TeV energy range. The detection technique used by IACT as well as the specificities of the reconstruction method of H.E.S.S. I (first phase of the H.E.S.S. experiment) are fully described in this thesis. After more than ten years of activity the H.E.S.S. experiment has registered a large amount of data. In addition to the regions of interest that its detectors probe and where astrophysical sources were unveiled, many events collected provide useful information on their surrounding environment. Indeed, acting as a background to the active sources, one can find the diffuse emissions, which are not well understood and yet are of significant interest for astrophysics, particle physics, cosmology and even physics beyond standard models, such as the search for dark matter. The diffuse emissions and their previous studies are presented in this thesis, as well as their possible origin, starting from the acceleration of cosmic-rays mechanism and the gamma-ray production in the active sources or from secondary process involving cosmic-rays interactions in the interstellar medium.In this work, tools to investigate the diffuse emissions were developed. The approach aims at disentangling the different components of the studied data so as to extract an estimation of their weight in the spectrum. It takes into account two aspects, explained separately in this thesis. On the one hand, the morphology of the active source in the studied field of view is used to modelize it and obtain its spectrum. Then, to disentangle the different contributions in the background, the method is based on probability density functions (PDF) built with discriminant variables. The necessary preliminary study and manipulation of the discriminant variables is also detailed. Well known astrophysical sources are used as benchmarks for the analysis. The resulting spectra for the active source, diffuse electrons and hadrons are presented and discussed, in addition to an upper limit on the extragalactic diffuse gamma-ray emission flux. The associated systematic errors were estimated
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Wikström, Gustav. "A search for solar dark matter with the IceCube neutrino telescope." Doctoral thesis, Stockholms universitet, Fysikum, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-27352.
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Dark matter particles in the form of supersymmetric Weakly Interacting Massive Particles (WIMPs) could accumulate in the centre of the Sun because of gravitational trapping. Pair-wise annihilations of WIMPs could create standard model particles out of which neutrinos could reach the Earth. Data from the IceCube 22-string neutrino telescope have been searched for signals from dark matter annihilations in the Sun. Highly sophisticated analysis methods have been developed to discern signal neutrinos from the severe background of atmospheric particle showers. No signal has been found in a dataset of 104 days livetime taken in 2007, and an upper limit has been placed on the muon flux in the South Pole ice induced by neutrinos from the Sun, reaching down to 330 km-2y-1. The flux limit has been converted into an upper limit on the neutralino scattering cross-section, which reaches down to 2.8*10-40 cm2 for spin-dependent interactions.Four articles are appended to the thesis:I. G. Wikström for the IceCube collaboration, Proc. of the 30th ICRC,arXiv/0711.0353 [astro-ph] (2007) 135.II. A. Gross, C. Ha, C. Rott, M. Tluczykont, E. Resconi, T. DeYoung and G. Wikström for the IceCube Collaboration, Proc. of the 30th ICRC,arXiv/0711.0353 [astro-ph] (2007) 11.III. G. Wikström and J. Edsjö, JCAP 04 (2009) 009.IV. R. Abbasi et al. (IceCube collaboration), accepted for publication in Phys. Rev. Lett., arXiv/0902.2460v3 [astro-ph.CO] (2009).
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Halladjian, Garabed. "Recherche de neutrinos cosmiques de haute-énergie émis par des sources ponctuelles avec ANTARES." Phd thesis, Université de la Méditerranée - Aix-Marseille II, 2010. http://tel.archives-ouvertes.fr/tel-00798866.
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L'objectif de cette thèse est la recherche des neutrinos cosmiques de haute énergie émis par des sources ponctuelles avec le télescope á neutrino ANTARES. La détection des neutrinos cosmiques de haute énergie peut apporter des réponses à des problèmes importants comme l'origine des rayons cosmiques et les procédures d'émission des rayons $\gamma$. Dans la première partie de la thèse, le flux des neutrinos émis par des sources galactiques et extragalactiques et le nombre des événements qui peut être détecté par ANTARES sont estimés. Cette étude utilise les spectres des rayons $\gamma$ des sources connues en tenant compte de l'absorption de ces rayons par la lumière extragalactique diffuse. Dans la deuxième partie de la thèse, le pointage absolu du télescope ANTARES est étudié. Étant situé à une profondeur de 2475 m dans l'eau de mer, l'orientation du détecteur est déterminée par un système de positionnement acoustique qui utilise des ondes de basse et haute fréquences entre la surface de la mer et le fond. La troisième partie de la thèse est la recherche des sources ponctuelles de neutrinos avec les données d'ANTARES. L'algorithme de recherche est basé sur une méthode de maximisation du rapport de vraisemblance. Il est utilisé dans deux stratégies de recherche; ''la stratégie de recherche avec des sources candidates'' et ''la stratégie de recherche dans tout le ciel''. L'analyse des données de 2007+2008 n'a pas marqué une découverte. Les meilleures limites supérieures au monde sur les flux de neutrinos provenant des différentes sources dans l'Hémisphère Sud sont établies.
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Jendrysik, Christian [Verfasser], Siegfried [Akademischer Betreuer] Bethke, and Jonathan J. [Akademischer Betreuer] Finley. "Development and characterisation of silicon photomultipliers with bulk-integrated quench resistors for future applications in particle and astroparticle physics / Christian Jendrysik. Gutachter: Jonathan J. Finley ; Siegfried Bethke. Betreuer: Siegfried Bethke." München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1054419868/34.
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Casey, James David. "Search for high energy GRB neutrinos in IceCube." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53839.
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The IceCube Neutrino Observatory has reported the observation of 35 neutrino events above 30 TeV with evidence for an astrophysical neutrino flux using data collected from May 2010 to May 2013. These events provide the first high-energy astrophysical neutrino flux ever observed. The sources of these events are currently unknown. IceCube has looked for correlations between these events and a list of TeV photon sources including a catalog of 36 galactic sources and 42 extragalactic sources, correlations with the galactic plane and center, and spatial and temporal clustering. These searches have shown no significant correlations. The isotropic distribution of the event directions gives indications that the events could be extragalactic in nature and therefore may originate in the same processes that generate ultra-high-energy cosmic rays (UHECRs). The sources of these UHECRs are still unknown; however, gamma-ray bursts (GRBs) have been proposed as one possible source class. By determining the source of these high-energy neutrinos, it may be possible to determine the sources of UHECRs as well. This study is a search for directional and temporal correlation between 856 GRBs and the astrophysical neutrino flux observed by IceCube. Nearly 10,000 expanding time windows centered on the earliest reported time of the burst were examined. The time windows start at ±10 s and extend to ±15 days. We find no evidence of correlations for these time windows and set an upper limit on the fraction of the astrophysical flux that can be attributed to the observed GRBs as a function of the time window. GRBs can contribute at most 12% of the astrophysical neutrino flux if the neutrino-GRB correlation time is less than ≈20 hours, and no more than 38% of the astrophysical neutrino flux can be attributed to the known GRBs at time scales up to 15 days. We conclude that GRBs observable by satellites are not solely responsible for IceCube’s astrophysical neutrino flux, even if very long correlation time scales are assumed.
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Cheymol, Benjamin. "Développement des instruments de mesures des profiles transversaux et d'emittance pour l'accélérateur linéaire LINAC4 au CERN." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2011. http://tel.archives-ouvertes.fr/tel-00877031.
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Dans les prochaines années, le complexe d'accélérateur du CERN va subir une profonde mise a jour dont le but est une augmentation de la luminosité du LHC. Le projet LIU ( LHC Injectors Upgrade) coordonne les mises a jour des différentes parties de la chaine d'injection. Le projet LINAC4 s'inscrit dans ce cadre et sera la première étape de la mise à jour. Cette thèse présente les différentes études conduites lors du développement de l'instrumentation nécessaire à la mesure du faisceau. Ce travail est limité aux instruments permettant la mesure des profils transverses (taille et emittance). La thèse se divise en quatre parties. La première partie, composée des trois premiers chapitres, est vue comme une partie d'introduction où il sera présenté le projet LINAC4 ainsi que les différents aperçus théoriques nécessaires à la conception de types d'instruments requis. Le chapitre 2 décrit brièvement la dynamique des faisceaux dans un accélérateur et présente également des rappels théoriques sur l'effet de charge d'espace induit par le faisceau. Le chapitre 3 est un rappel sur les interactions entre particules et matière. La seconde partie, comprenant les chapitres 4 a 6, décrit les différentes études menées lors de la conception des SEM grid, wire scanner et emittance mètre. Le lecteur trouvera dans cette partie une description des instruments mentionnés et qui seront déployés lors de la phase de test et pendant la phase d'opération du LINAC4. Le chapitre 4 s'attarde sur les effet de charge thermique induite sur les fils des SEM grid et wire beam scanner par le faisceau et leur conséquence sur la survit de ces fils. Le LINAC4 va produire un faisceau intense d'ion H-, avec une taille de faisceau de l'ordre du millimètre, cette densité de particule va, à basse énergie, induire un grand dépôt d'énergie dans la matière. La hausse de température qui en résulte peut dépasser les limites thermomécaniques des matériaux usuels employés pour ce type de mesure. Cette étude permet de déterminer le matériau idéal pour le fil et d'imposer certaines restrictions sur l'utilisation des différents moniteurs de profils. Au sein de ce chapitre il est aussi présente une estimation des signaux obtenus pour des géométries et des matériaux de fils différents. Les chapitres 5 et 6 sont une études de l'emittance mètre a moyenne énergie du LINAC4 (3 et 12 MeV), le système employé est un système dit "Slit & grid", ou une fente permet de sélectionner une faible partie du faisceau, le reste étant absorbé, le profil du faisceau non perturbé est mesuré par une grille. Le chapitre 5 présente une étude sur les erreurs systématiques des mesures d'emittance dû a la diffusion multiple et a l'effet de charge d'espace du faisceau, ces deux phénomènes constituant les principales erreurs conduisant à une mauvaise reconstruction de l'emittance mesurée. Le chapitre 6 quant a lui est dédié à l'étude mécanique de la fente de l'emittance mètre. Comme pour les fils des moniteurs de profils, la charge thermique sur la partie supportant la slit est importante. Ce chapitre décrit les études effectuées pour le choix des matériaux et de la géométrie des pièces mécaniques. La troisième partie de la thèse, qui se résume au chapitre 7, est consacrée aux différents résultats expérimentaux obtenus dans la phase de test de la source de particule du LINAC4 ainsi que ceux obtenus lors d'une visite d'étude à SNS. Une partie de se chapitre décrira la mise au point de l'instrumentation aux banc test de la source, une autre présente l'effet de la diffusion multiple sur les mesures d'emittance à SNS et propose une mise a jour de l'instrument. Le chapitre 8 constitue la dernière partie de cette thèse. Dans ce dernier chapitre, le lecteur pourra lire une étude préliminaire sur l'utilisation d'un faisceau laser pour la mesure d'emittance et de profil aux hautes énergies du linac.
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Dolgorouky, Youri. "Optimisation du pouvoir de résolution et du rejet du fond radioactif de détecteurs ionisation-chaleur équipés de couches minces thermométriques pour la détection directe de WIMPs." Phd thesis, Université Paris Sud - Paris XI, 2008. http://tel.archives-ouvertes.fr/tel-00401690.
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Pour la recherche de la matière noire sous forme de WIMPs l'expérience EDELWEISS utilise des détecteurs ionisation-chaleur qui permettent de les discriminer du fond radioactif. Cette méthode est limitée par les événements à collecte incomplète de charge qui ont lieu près des électrodes. Dans le but d'identifier et rejeter ces événements, des détecteurs équipés de couches minces servant à la fois de thermomètres, sensibles au régime thermique transitoire (régime athermique), et d'électrodes de collecte sont développés. Leur optimisation en terme de rejet des événements de surface et la modélisation des processus physiques permettant cette identification font l'objet de cette thèse. L'optimisation doit conserver une résolution en énergie qui conduise à un seuil de l'ordre de 30 keV et un volume fiduciel de détecteur maximal. Ce travail explore quatre générations de détecteurs qui correspondent à des évolutions successives de leur conception. Dans tous les cas l'électrode-thermomètre est une couche mince de NbSi amorphe de type isolant d'Anderson polarisée par deux peignes interdigités en Niobium. En dépit des progrès réalisés la génération la plus aboutie ne présente pas les performances requises pour l'expérience EDELWEISS II. L'étude menée a montré la difficulté de la modélisation des signaux thermique transitoires car la collecte des charges y apporte des contributions complexes. Des pistes émergent de ce travail pour explorer de nouvelles configuration de ces détecteurs afin d'exploiter mieux le régime athermique pour améliorer le pouvoir de rejet et la résolution.
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Kahlhoefer, Felix Karl David. "Complementarity of searches for dark matter." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:ec5b1afe-b75c-44d9-9dad-e0d342e46fa1.
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The striking evidence for the existence of dark matter in the Universe implies that there is new physics to be discovered beyond the Standard Model. To identify the nature of this dark matter is a key task for modern astroparticle physics, and a large number of experiments pursuing a range of different search strategies have been developed to solve it. The topic of this thesis is the complementarity of these different experiments and the issue of how to combine the information from different searches independently of experimental and theoretical uncertainties. The first part focuses on the direct detection of dark matter scattering in nuclear recoil detectors, with a special emphasis on the impact of the assumed velocity distribution of Galactic dark matter particles. By converting experimental data to variables that make the astrophysical unknowns explicit, different experiments can be compared without implicit assumptions concerning the dark matter halo. We extend this framework to include annual modulation signals and apply it to recent experimental hints for dark matter, showing that the tension between these results and constraints from other experiments is independent of astrophysical uncertainties. We explore possible ways of ameliorating this tension by changing our assumptions on the properties of dark matter interactions. In this context, we propose a new approach for inferring the properties of the dark matter particle, which does not require any assumptions about the structure of the dark matter halo. A particularly interesting option is to study dark matter particles that couple differently to protons and neutrons (so-called isospin-violating dark matter). Such isospin-violation arises naturally in models where the vector mediator is the gauge boson of a new U(1) that mixes with the Standard Model gauge bosons. In the second part, we first discuss the case where both the Z' and the dark matter particle have a mass of a few GeV and then turn to the case where the Z' is significantly heavier. While the former case is most strongly constrained by precision measurements from LEP and B-factories, the latter scenario can be probed with great sensitivity at the LHC using monojet and monophoton searches, as well as searches for resonances in dijet, dilepton and diboson final states. Finally, we study models of dark matter where loop contributions are important for a comparison of LHC searches and direct detection experiments. This is the case for dark matter interactions with Yukawa-like couplings to quarks and for interactions that lead to spin-dependent or momentum suppressed scattering cross sections at tree level. We find that including the contribution from heavy-quark loops can significantly alter the conclusions obtained from a tree-level analysis.
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Lund, Jens. "Antiparticle identification studies for the PAMELA satellite experiment." Doctoral thesis, KTH, Physics, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-40.
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The PAMELA satellite experiment will soon be launched and during its 3 year mission perform measurement of charged particle fluxes in the cosmic radiation. PAMELA is specifically designed to identify antiprotons and positrons in the vast background of other charged particles. These antiparticle measurements will be performed using: a permanent magnet spectrometer, a scintillator based time of flight system, an electromagnetic imaging calorimeter, a transition radiation detector and a scintillator triggered neutron detector. There is also a scintillator based anticoincidence system to reject spurious triggers from out of acceptance events (developed and built at KTH). These detectors will allow the background in the antiproton and positron measurements to be significantly reduced, and PAMELA will thus be able to perform high precision measurements with unprecedented statistics and over a wide energy range, far surpassing any previous experiment. To determine the antiparticle identification and background rejection capability of the experiment, studies have been performed using simulations and data collected at particle beams. These studies have focused on: the proton rejection in positron measurements (using the calorimeter), contamination by locally produced pions in antiproton measurements and estimations of the expected statistics due to the energy dependence (caused by e.g. the geomagnetic field and the magnetic field in the spectrometer) of the gathering power. This work significantly extends previous studies of the PAMELA performance in antiparticle identification.
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Fleischhack, Henrike. "Measurement of the iron spectrum in cosmic rays with the VERITAS experiment." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2017. http://dx.doi.org/10.18452/17691.
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Das Energiespektrum der kosmischen Strahlung bietet wichtige Hinweise auf ihren Ursprung und ihre Ausbreitung. Verschiedene Messtechniken müssen kombiniert werden, um den ganzen Energiebereich abdecken zu können: Direkte Messungen mit Teilchendetektoren bei niedrigen Energien sowie indirekte Messungen von Luftschauern bei hohen Energien. Dazu kommt die Messung von Photonen, hauptsächlich im GeV- und TeV-Bereich, die bei der Wechselwirkung von kosmischer Strahlung mit Materie oder elektromagnetischen Feldern entstehen. Im Folgenden werde ich zwei Studien dazu vorstellen, die beide auf Daten des abbildenden Tscherenkow-Teleskopes VERITAS beruhen. Erstens stelle ich eine Messung das Energiespektrums von Eisenkernen in der kosmischen Strahlung vor. Für die Bestimmung der Energie und Ankunftsrichtung der Primärteilchen benutze ich eine neuartige Template-Likelihood-Methode, die hier erstmals auf Eisenschauer angewendet wird. Zur Identifizierung der Eisenschauer benutze ich unter anderem das sogenannte direkte Tscherenkow-Licht, welches von geladenen Teilchen vor der ersten Wechselwirkung ausgestrahlt wird. Dazu kommt eine multivariate Klassifizierungsmethode, um den Verbleibenden Untergrund zu charakterisieren. Das so gemessene Energiespektrum von Eisen wird im Bereich von 20 TeV bis 500 TeV gut durch ein Potenzgesetz beschrieben. Zweitens beschreibe ich eine Suche nach Gammastrahlung oberhalb von 100 GeV von den drei Galaxien Arp 220, IRAS 17208-0014 und IC 342. Diese drei Galaxien haben hohe Sternentstehungsraten und daher viele Supernova-Überreste, welche kosmische Strahlung erzeugen. Diese wechselwirkt erwartungshalber mit den dichten Staubwolken in den Sternentstehungsgebieten und erzeugt Gammastrahlung. VERITAS konnte keine solche Gammastrahlung messen. Die daraus abgeleitete Höchstgrenze für die Luminosität schränkt theoretische Modelle der Erzeugung und Propagation von kosmischer Strahlung in der Galaxie Arp 220 ein.The energy spectrum of cosmic rays can provide important clues as to their origin and propagation. Different experimental techniques have to be combined to cover the full energy range: Direct detection experiments at lower energies and indirect detection via air showers at higher energies. In addition to detecting cosmic rays at Earth, we can also study them via the electromagnetic radiation, in particular gamma rays, that they emit in interactions with gas, dust, and electromagnetic fields near the acceleration regions or in interstellar space. In the following I will present two studies, both using data taken by the imaging air Cherenkov telescope (IACT) VERITAS. First, I present a measurement of the cosmic ray iron energy spectrum. I use a novel template likelihood method to reconstruct the primary energy and arrival direction, which is for the first time adapted for the use with iron-induced showers. I further use the presence of direct Cherenkov light emitted by charged primary particles before the first interaction to identify iron-induced showers, and a multi-variate classifier to measure the remaining background contribution. The energy spectrum of iron nuclei is well described by a power law in the energy range of 20 to 500 TeV. Second, I present a search for gamma-ray emission above 100 GeV from the three star-forming galaxies Arp 220, IRAS 17208-0014, and IC342. Galaxies with high star formation rates contain many young and middle-aged supernova remnants, which accelerate cosmic rays. These cosmic rays are expected to interact with the dense interstellar medium in the star-forming regions to emit gamma-ray photons up to very high energies. No gamma-ray emission is detected from the studied objects and the resulting limits begin to constrain theoretical models of the cosmic ray acceleration and propagation in Arp 220.
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Lundström, Erik. "Phenomenology of Inert Scalar and Supersymmetric Dark Matter." Doctoral thesis, Stockholms universitet, Fysikum, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-39278.
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While the dark matter has so far only revealed itself through the gravitational influence it exerts on its surroundings, there are good reasons to believe it is made up by WIMPs – a hypothetical class of heavy elementary particles not encompassed by the Standard Model of particle physics. The Inert Doublet Model constitutes a simple extension of the Standard Model Higgs sector. The model provides a new set of scalar particles, denoted inert scalars because of their lack of direct coupling to matter, of which the lightest is a WIMP dark matter candidate. Another popular Standard Model extension is that of supersymmetry. In the most minimal scenario the particle content is roughly doubled, and the lightest of the new supersymmetric particles, which typically is a neutralino, is a WIMP dark matter candidate. In this thesis the phenomenology of inert scalar and supersymmetric dark matter is studied. Relic density calculations are performed, and experimental signatures in indirect detection experiments and accelerator searches are derived. The Inert Doublet Model shows promising prospects for indirect detection of dark matter annihilations into monochromatic photons. It is also constrained by the old LEP II accelerator data. Some phenomenological differences between the Minimal Supersymmetric Standard Model and a slight extension, the Beyond the Minimal Supersymmetric Standard Model, can be found. Also, supersymmetric dark matter models can be detected already within the early LHC accelerator data.
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Stasik, Alexander Johannes. "Search for High Energetic Neutrinos from Core Collapse Supernovae using the IceCube Neutrino Telescope." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/18729.
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Die Entdeckung eines hochenergetischen Flusses astrophysikalischer Neutrinos stellt einen wesentlichen physikalischen Durchbruch der letzten Jahre dar. Trotz allem ist der Ursprung dieser Neutrinos immer noch unbekannt. Die Suche nach den Quellen der hochenergetischen kosmischen Strahlung ist direkt verbunden mit der Suche nach Neutrinos, da diese in den gleichen hadronischen Prozessen erzeugt werden und eine Neutrinoquelle deshalb einen direkten Hinweis auf eine Quelle der kosmischen Strahlung darstellen würde. Viele potentielle Quellen der Neutrinos werden diskutiert, darunter Kern-Kollaps Supernovae.
In dieser Arbeit werden sieben Jahre Daten des IceCube Neutrinoteleskopes mit der Richtung mehreren Hundert Kernkollaps-Supernovae auf Korrelation getestet. Die Analyse gewinnt dabei durch die gute Richtungsrekonstruktion der 700000 Muonspurdaten und der großen Datenbank optische beobachteter Supernovae. Die Sensitivität der zeitabhängigen Likelihood-Analyse wird durch die Kombination mehrere Quellen in einer einzigen Analyse gesteigert.
Es wurde kein statistisch signifikantes Cluster von Neutrinos an den Positionen der Supernovae gefunden. Daraus wurden obere Grenzen für verschiedene Modelle berechnet und der Beitrag von Kernkollaps-Supernovae zum diffusen Neutrinofluss eingeschränkt. Daraus können bestimmte Typen von Supernovae als dominate Quelle der diffusen hochenergetischen astrophysikalischen Neutrinos ausgeschlossen werden.The recent discovery of a high energy flux of astrophysical neutrinos was one of the breakthroughs of the last years. However, the origin of these neutrinos remains still unknown. Also, the search for the sources of high-energy cosmic rays is closely connected to neutrinos since neutrinos are produced in hadronic interactions, and thus the detection of a neutrino source would be a \textit{smoking gun} signature for cosmic rays. Many potential neutrino source classes have been discussed, among these are core-collapse supernovae. In this thesis, seven years of data from the IceCube neutrino observatory are tested for correlation with the direction of hundreds of core-collapse supernovae. The analysis benefits from the good angular reconstruction of the order of one degree and below of the about 700000 muon track events and an extensive database of optical observations of supernovae. Using a time-dependent likelihood method, the sensitivity of the analysis is increased by stacking the sources in a combined analysis. No significant clustering of neutrino events around the position of core-collapse supernovae is found. Upper limits of different neutrino light curve models are computed, and the contribution of core-collapse supernovae to the measured diffuse high energetic neutrino background is constrained. These limits allow excluding certain types of core-collapse supernovae as the dominant source of the observed high energetic astrophysical neutrino flux.
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Billard, Julien. "Détection directionnelle de matière sombre avec MIMAC." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00727557.
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De nombreuses mesures cosmologiques et astrophysiques tendent à montrer que notre galaxie serait englobée par un halo de matière sombre non-baryonique. La détection directionnelle vise à mesurer la direction du recul nucléaire issu d'une interaction avec une particule de matière sombre. Cela permettrait de mettre en évidence la forte dépendance angulaire de la distribution de reculs due à la rotation du système solaire autour du centre galactique. Cette thèse aborde la détection directionnelle par une approche multi-thématique : phénoménologie, expérimentale et analyse de données. L'objectif des études phénoménologiques est de montrer l'apport d'un détecteur directionnel en terme de recherche de matière sombre. Grâce au développement de méthodes statistiques dédiées, on montre qu'un détecteur tel que celui proposé par la collaboration MIMAC, devrait permettre de découvrir la matière sombre avec une grande significance jusqu'à des sections efficaces 2 à 3 ordres de grandeur en dessous des limites actuelles. La mise en place d'une méthodologie d'analyse de données directionnelles constitue un second objectif de cette thèse car la reconstruction 3D des traces mesurées est un point clef de cette nouvelle stratégie de détection. On présente ainsi une nouvelle méthode d'analyse basée sur une approche par vraisemblance, permettant d'optimiser l'estimation des paramètres de chaque événement mesuré: position dans le détecteur et direction. Dans le cadre de la discrimination du bruit de fond électronique, on a mis en place une étude basée sur la topologie de la trace et utilisant une analyse par arbres de décision boostés qui nous permet d'obtenir des facteurs de rejet environ 20 fois supérieurs à ceux obtenus avec des analyses séquentielles. Du point de vue expérimental, on présente une méthode originale de la mesure de vitesse de dérive des électrons permettant d'obtenir des incertitudes de l'ordre du pourcent et de contraindre simultanément les coefficients de diffusion longitudinale. On termine enfin sur l'analyse des données obtenues auprès du champ de neutrons AMANDE permettant de valider la stratégie de détection du projet MIMAC.
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Ylinen, Tomi. "Search for Gamma-ray Lines from Dark Matter with the Fermi Large Area Telescope." Doctoral thesis, KTH, Partikel- och astropartikelfysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12853.
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Dark matter (DM) constitutes one of the most intriguing but so far unresolved issues in physics. In many extensions of the Standard Model of particle physics, the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent DM particle candidate. One of the most interesting scenarios is the creation of monochromatic gamma-rays from the annihilation or decay of these particles. This type of signal would represent a “smoking gun” for DM, since no other known astrophysical process should be able to produce it. In this thesis, the search for spectral lines with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi) is presented. The satellite was successfully launched from Cape Canaveral in Florida, USA, on 11 June, 2008. The energy resolution and performance of the detector are both key factors in the search and are investigated here using beam test data, taken at CERN in 2006 with a scaled-down version of the Fermi-LAT instrument. A variety of statistical methods, based on both hypothesis tests and confidence interval calculations, are then reviewed and tested in terms of their statistical power and coverage. A selection of the statistical methods are further developed into peak finding algorithms and applied to a simulated data set called obssim2, which corresponds to one year of observations with the Fermi-LAT instrument, and to almost one year of Fermi-LAT data in the energy range 20–300 GeV. The analysis on Fermi-LAT data yielded no detection of spectral lines, so limits are placed on the velocity-averaged cross-section, QC20100525
GLAST
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McBride, Keith William. "Cosmic Ray Instrumentation and Simulations." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1620666030783043.
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Akrami, Yashar. "Supersymmetry vis-à-vis Observation : Dark Matter Constraints, Global Fits and Statistical Issues." Doctoral thesis, Stockholms universitet, Fysikum, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-57194.
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Weak-scale supersymmetry is one of the most favoured theories beyond the Standard Model of particle physics that elegantly solves various theoretical and observational problems in both particle physics and cosmology. In this thesis, I describe the theoretical foundations of supersymmetry, issues that it can address and concrete supersymmetric models that are widely used in phenomenological studies. I discuss how the predictions of supersymmetric models may be compared with observational data from both colliders and cosmology. I show why constraints on supersymmetric parameters by direct and indirect searches of particle dark matter are of particular interest in this respect. Gamma-ray observations of astrophysical sources, in particular dwarf spheroidal galaxies, by the Fermi satellite, and recording nuclear recoil events and energies by future ton-scale direct detection experiments are shown to provide powerful tools in searches for supersymmetric dark matter and estimating supersymmetric parameters. I discuss some major statistical issues in supersymmetric global fits to experimental data. In particular, I further demonstrate that existing advanced scanning techniques may fail in correctly mapping the statistical properties of the parameter spaces even for the simplest supersymmetric models. Complementary scanning methods based on Genetic Algorithms are proposed.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.
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Giomi, Matteo. "A catalog of variable high-energy gamma-ray sources and prospects for polarization measurement with the Fermi Large Area Telescope." Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/18596.
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Das Fermi Large Area Telescope (LAT) ist ein satellitengestütztes Gammastrahlungs-Teleskop zur Messung von Gammastrahlung im Energiebereich zwischen ∼ 30 MeV und mehreren hundert GeV. Der Nachweis extraterrestrischer Gammastrahlung in diesem Energiebereich erlaubt Rückschlüsse auf die astrophysikalischen Quellen der Gammastrahlung und Beschleunigungsmechanismen kosmischer Strahlung mit Energien zwischen 1 GeV und ∼ 10 TeV. Die Beobachtung von Quellen während Phasen vorübergehend erhöhter Gammastrahlungslüsse (‘Flares’) ermöglicht dabei eine besonders empfindliche Untersuchung der Produktionsmechanismen kosmischer Strahlung in den Quellen, da die Eigenschaften kürzlich beschleunigter Teilchen unmittelbar studiert werden können.
Der Hauptteil dieser Dissertation stellt das neueste Verzeichnis zeitlich variabler Gammastrahlungsquellen über 100 MeV vor, den zweiten ‘Fermi All-sky Variability Analysis’ Katalog (2FAV). Der 2FAV Katalog enthält über 4500 Flares, welche in den ersten 7.4 Jahren der LAT Datennahme auf einem hohen Vertrauensniveau gemessen und an 518 verschiedenen Himmelspositionen beobachtet wurden. 441 dieser Quellpositionen im 2FAV können Aktiven Galaktischen Kernen (AGN) zugeordnet werden. Die verbleibenden 77 Quellpositionen besitzen keine sichere Entsprechung in anderen Verzeichnissen von Gammastrahlungs- oder Blazarquellen und stellen möglicherweise neue Gammastrahlungsquellen dar. Bei der Untersuchung der Spektren der 2FAV Flares, welche sogenannten ‘Flat-Spectrum’ Radioquasaren (FSRQ) - eine Unterklasse der AGN - zugeordnet werden können, wurde durchweg ein härteres Gammastrahlungsspektrum während Phasen erhöhter Gammastrahlungsemission beobachtet. Zudem wurde eine Untergrenze in der Verteilung der spektralen Exponenten, Γ ≳ 1.5, in der Stichprobe der untersuchten Flares festgestellt. Unter der Annahme eines einfachen leptonischen Modells und dass die Verteilung beschleunigter Teilchen im Inertialsystem der Quelle isotrop ist, folgt daraus, dass die Energiespektren der kosmischen Strahlung, welche die Gammastrahlungs-Flares verursachen, mit dN/dE ∝ E −2 oder stärker abfallen.
Eine andere Möglichkeit, die Beschleunigungsmechanismen kosmischer Strahlung zu untersuchen, ist die Messung der Polarisation der begleitenden Gammastrahlung. Der letzte Teil dieser Dissertation enthält eine vorläufige Studie zur Messbarkeit linearer Polarisation astrophysikalischer Gammastrahlung mit dem LAT-Instrument. Bei Konversion hochenergetischer Photonen in Elektron-Positron-Paare verursacht eine lineare Polarisation der Gammastrahlung eine Modulation des Azimutwinkels der Ebenen, in denen die Elektron-Positron-Paare erzeugt wurden. Obwohl der LAT ursprünglich nicht als Polarimeter konzipiert wurde, ermöglicht das Instrument eine Messung dieser Modulation für niederenergetische Primärteilchen (≲ 200 MeV), welche in den Silikonschichten des Detektors konvertieren. Eine Auswahl solcher Ereignisse, selektiert durch Algorithmen überwachten maschinelles Lernens (‘supervised machine learning’), wird verwendet um die statistischen und systematischen Messunsicherheiten abzuschätzen, denen eine Messung unterworfen ist. Werden allein statistische Unsicherheiten berücksichtigt, ist der LAT in der Lage, einen Polarisationsgrad von 30−50% der Gammastrahlungsflüsse vom Vela-Pulsar und vom Krebs-Pulsarwindnebels nach einer Beobachtungszeit von zehn Jahren auf einem Vertrauensniveau von 5σ nachzuweisen. Werden zusätzlich systematische Unsicherheiten berücksichtigt, wird abgeschätzt, dass ein Polarisationsgrad von ∼ 46% auf einem Vertrauensniveau von 5σ nachweisbar ist, indem eine Auswahl von AGN als unpolarisierte Testprobe verwendet und mit umfangreichen Monte-Carlo Simulationen verglichen wird. Die Analyse in dieser Dissertation berücksichtigt zum ersten Mal sämtliche Aspekte einer polarization-sensitiven Ereignissrekonstruktion und dienst damit als Grundlage für zukünftige Nachweisversuche der Polarisation astrophysikalischer Gammastrahlung mit dem LAT.The Fermi Large Area Telescope (LAT) is a space-based pair-conversion telescope sensitive to gamma rays with energies from ∼ 30 MeV to several hundreds of GeV. Observing gamma rays in this energy range, we gain information on the sources and acceleration mechanisms of cosmic rays (CRs) of energies from ∼ 1 GeV to ∼ 10 TeV. Studying the emission of gamma-ray sources during periods of enhanced activity (flares) provides a sensitive probe of the production mechanisms of CRs, as it makes it possible to investigate the distributions of the freshly-accelerated particles. The main part of this work presents the latest catalog of variable gamma-ray sources above 100 MeV, the second Fermi All-sky Variability Analysis catalog (2FAV). The 2FAV catalog contains more than 4500 flares detected at high significance in the first 7.4 years of LAT observations and the 518 sources from which these flares originate. Probable counterparts, mostly active galactic nuclei (AGN), have been found for 441 sources in the 2FAV. The remaining 77 sources have no reliable counterparts in other gamma-ray or blazar catalogs; they are potentially new gamma-ray sources. Studying the spectra of the 2FAV flares, we observe a harder-when-brighter behavior for the entire sample of flares associated with lat spectrum radio quasars, a class of AGN. We also observe a minimum value in the distribution of the photon index Γ of the flares, corresponding to Γ ≳ 1.5. In a simple leptonic scenario, assuming that the distribution of accelerated particles is isotropic in the source reference frame, this limit on the spectral hardness implies that the spectra of the accelerated particles responsible for the lare is never harder than dN/dE ∝ E −2. Another way to probe the environments where CRs are accelerated is by measuring the polarization of the gamma rays. A preliminary study of the LAT sensitivity to linear polarization of astrophysical gamma-rays is presented in the last part of this thesis. In the pair-production regime, linear polarization of the gamma-rays induces a modulation in the azimuthal angle of the planes where the electron-positron pairs are produced. Although not designed as a polarimeter, the LAT has the potential to measure this modulation using low energy (≲ 200 MeV) events converting in the silicon detector layers of its tracker. A selection of these events using supervised machine learning algorithms is presented and used as a basis to estimate the statistical and systematic uncertainties afecting the measurement. Considering only statistical uncertainties, a degree of polarization of ∼ 30−50% could be detected at the 5σ confidence level for the Vela pulsar and the Crab pulsar-wind nebula after 10 years of observation. By including systematic uncertainties, a 5σ sensitivity limit corresponding to a polarization degree of ∼ 46% is estimated, using a stack of AGN as an unpolarized test source and comparing the data with detailed Monte Carlo simulations. This analysis addresses for the first time all the steps of a real measurement and can therefore provide the basis for future measurements of gamma-ray polarization with the LAT.
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Stafford, Samuel J. "A Search for Ultra-high Energy Cosmic Neutrinos: Data Analysis of the Antarctic Impulsive Transient Antenna, Third Flight." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1500417877886765.
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Stachurska, Juliana. "Astrophysical Tau Neutrinos in IceCube." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21611.
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Das IceCube Neutrino Observatorium am Südpol hat die Existenz eines diffusen astrophysikalischen Neutrinoflusses nachgewiesen. Die Flavor-Zusammensetzung astrophysikalischer Neutrinos trägt Informationen über Orte kosmischer Teilchenbeschleunigung und Auswirkungen potenzieller neuer Physik auf die Neutrinoausbreitung. Zur seiner Bestimmung ist die Beobachtung von Tau-Neutrinos nötig. Ab einer Energie von ~O(100 TeV) kann deren Wechselwirkung über geladene Ströme eine Doppelkaskaden-Topologie ergeben, bei der die zwei Energiedepositionen am Tau-Entstehungs- und Tau-Zerfallsvertex aufgelöst werden können. Diese wird zusammen mit den bereits bekannten Topologien Einzel-Kaskade und Spur zur Messung der Flavor-Zusammensetzung auf der Erde benutzt. In dieser Arbeit werden im Detektorvolumen von IceCube anfangende Ereignisse mit hohen Energien algorithmisch in drei Topologien klassifiziert. Im Datensatz mit einer Lebensdauer von 7.5 Jahren werden zum ersten Mal zwei Doppelkaskaden identifiziert; diese sind Kandidaten für Tau-Neutrinos. Die Eigenschaften der zwei Tau-Neutrino-Kandidaten werden in einer a-posteriori Analyse im Detail studiert. Die statistische Methode wird durch einen Log-Likelihood-Quotienten-Test mit multi-dimensionalen Wahrscheinlichkeitsdichten verbessert. Eine der Doppelkaskaden ist konsistent mit dem Szenario einer misklassifizierten Einzelkaskade, während für die zweite Doppelkaskade die Wahrscheinlichkeit eines nicht-Tau-Neutrino Szenarios auf nur 3% bestimmt wird. Die gemessene Flavor-Zusammensetzung ist konsistent mit der Annahme von astrophysikalischen Neutrinos sowie mit bisher veröffentlichen Resultaten. Die Messung ergibt einen astrophysikalischen Tau-Neutrino Fluss von dPhi / dE=3.0 (-1.8,+2.2) (E / 100TeV)^(-2.87) 10^(-18) GeV^(-1) cm^(-2) s^(-1) sr^(-1), was dem ersten positiven Ergebnis für die Tau-Normalisierung entspricht. Die Nichtexistenz eines astrophysikalischen Tau-Neutrino Flusses wird mit einer Signifikanz von 2.8 sigma abgelehnt.The IceCube neutrino observatory at the South Pole has confirmed the existence of a diffuse astrophysical neutrino flux. The flavor composition of astrophysical neutrinos carries information on the environments at the sites of cosmic particle acceleration as well as potential imprints of new physics acting during neutrino propagation. To measure the flavor composition the observation of the long-elusive tau neutrinos is required. Starting at an energy of ~O(100 TeV) a tau neutrino charged current interaction can produce a double cascade topology, where the two energy depositions from the tau creation and the tau decay vertices are resolvable. This topology together with the well-established track and single cascade topology is used to measure the flavor composition on Earth. In this work, high-energy events starting in IceCube's detector volume are classified algorithmically into the three topologies. In the dataset with a livetime of 7.5 years, two events are classified as double cascades for the first time, yielding multi-TeV tau-neutrino candidates. The properties of the two tau-neutrino candidates are investigated in an a-posteriori analysis. The statistical method is improved by performing a log-likelihood-ratio test using multi-dimensional probability densities. One of the double cascades is consistent with being a misclassified single cascade, while the second double cascade is found to have a misclassification probability of only 3%. The measured flavor composition nu_e:nu_mu:nu_tau = 0.20:0.39:0.42 is consistent with astrophysical neutrinos and with previously published results. The astrophysical tau-neutrino flux is measured to dPhi / dE=3.0 (-1.8,+2.2) (E / 100TeV)^(-2.87) 10^(-18) GeV^(-1) cm^(-2) s^(-1) sr^(-1) with spectral index gamma=2.87 (-0.20,+0.21), yielding the first non-zero results for the tau normalization. The absence of an astrophysical tau-neutrino flux is disfavored at 2.8 sigma.
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Scott, Pat. "Searches for Particle Dark Matter Dark stars, dark galaxies, dark halos and global supersymmetric fits /." Doctoral thesis, Stockholm : Department of Physics, Stockholm University, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-38221.
Full textAbstract:
Diss. (sammanfattning) Stockholm : Stockholms universitet, 2010.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Accepted. Paper 6: Submitted. Härtill 6 uppsatser.