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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
241

Background studies and design optimisation of the SuperNEMO demonstrator module : search for 2νββ and 0νββ decays of 116Cd into the excited states of 116Sn with NEMO-3 / Étude de bruit de fond et optimisation du design du module démonstrateur de SuperNEMO : recherche des désintégrations 2νββ et 0νββ du Cd-116 vers les états excités du Sn-116 avec NEMO-3

Le Noblet, Thibaud 26 September 2017 (has links)
Les détecteurs NEMO-3 et SuperNEMO ont été conçus pour la recherche de décroissance double bêta sans émission de neutrinos. Ces détecteurs fournissent une approche unique dans la recherche des événements double bêta en combinant des mesures à la fois de trajectoires, de temps de vol et d'énergie. De plus, grâce à la séparation de la source double bêta du reste du système de détection, les détecteurs NEMO ont la possibilité d'étudier plusieurs isotopes double bêta avec une forte réjection du bruit de fond.Cette thèse présente plusieurs études réalisées dans le cadre de l'optimisation et la préparation du détecteur SuperNEMO, successeur de NEMO-3. La première concerne l'optimisation des performances du détecteur en fonction de la configuration mécanique de ses feuilles sources. La conclusion de cette étude est que les deux configurations considérées sont équivalentes. La seconde étude s'intéresse à l'un des principaux bruits de fond que constitue le radon dans la recherche des désintégrations double bêta. Cette étude a été concrétisée par le développement et l'implémentation d'un algorithme permettant l'identification et la mesure des événements provenant de ce bruit de fond. Le deuxième volet de cette thèse rapporte l'analyse des données de NEMO-3 pour rechercher les décroissances double bêta avec et sans émission de neutrino du Cd-116 vers les états excités du Sn-116. Ces décroissances n'ont jamais été observées à ce jour, et les limites obtenus sur les états excités (2+) et (0+) sont les premières utilisant le détecteur NEMO-3. / The NEMO-3 and SuperNEMO detectors have been designed to search for neutrinoless double beta decays. These detectors provide a unique approach combining a calorimetric and a tracking measurement of double beta events emitted by a separated isotopic source. This approach allows to search for neutrinoless double beta decays among several isotopes with good background rejection. This thesis presents many studies performed for the optimisation and the preparation of the SuperNEMO detector, successor of NEMO-3. The first study concerns the optimisation of the detector performances with respect to the design of the source foil. The conclusion of this study is that the two configurations considered are equivalent. The second study focuses on the radon which constitutes one of the main background to the search for double beta decays. In this study an algorithm has been developed and implemented to search for the alpha particle allowing the identification and the measurement of the radon events. The thesis is completed by an analysis of the NEMO-3 data to search for the double beta decay of Cd-116 via the excited state of Sn-116. These decays have never been observed up to date and the limits set on the excited states (2+) and (0+) are the first using the NEMO-3 detector.
242

Massive Neutrinos: Phenomenological and Cosmological Consequences / Neutrinos Massivos: Consequências fenomenológicas e cosmológicas

Gonzalez, Yuber Ferney Perez 01 December 2017 (has links)
The XX century witnessed the quantum and relativistic revolutions in physics. The development of these two theories, namely, Quantum Mechanics and Relativity, was the inception of many crucial discoveries and technological advances. Among them, one stands out due to its uniqueness, the neutrino discovery. However, several neutrino properties are still obscure. Neutrinos are the only fundamental particles whose nature is currently unknown. Such fermions can either be different from their antiparticles, i.e., Dirac fermions, or be their own antiparticles, that is, Majorana fermions. On the other hand, the smallness of neutrino masses is a problem seemingly related to the neutrino nature; thus, as essential task consists in addressing the phenomenologically viable models in both cases. Furthermore, it is important to search for other physical process in which the neutrino nature may manifest through different experimental signatures. A rather difficult but promising method corresponds to the detection of the cosmic neutrino background, viz. neutrinos which are relics from the Big Bang. Previous works have shown that detection rates for Dirac and Majorana neutrinos can give different results. Nevertheless, this distinction was obtained considering the Standard Model framework only. Therefore, it is important to understand the consequences of having Non-Standard Interactions contributing to the detection of neutrinos from the cosmic background. Another remarkable relic predicted by Cosmology is the unidentified Dark Matter, composing ~25% of the Universe. All searches regarding the Weakly Interacting Massive Particle, one of the principal candidates for Dark Matter, have given negative results; this has compelled experiments to increase their sensitivity. Notwithstanding, neutrinos may stand in the way of such experimental searches given that they may constitute an irreducible background. In this thesis, we will address these three different phenomena, neutrino mass models, detection of the cosmic neutrino background and the neutrino background in Dark Matter searches, by considering the different characteristics in each case. In the study of neutrino mass models, we will consider models for both Majorana and Dirac neutrinos; specifically, we will probe the neutrinophilic two-Higgs-doublet model. Regarding the detection of relic neutrinos, we will analyse the consequences of the existence of the beyond Standard Model physics in the capture rate by tritium. Finally, we will scrutinize the impact of neutrinos in Direct Detection WIMP searches, by considering Standard Model plus additional interactions in the form of simplified models. / Ao longo do século XX testemunhamos as revoluções quântica e relativista que aconteceram na Física. O desenvolvimento da Mecânica quântica e da teoria da relatividade foi o prelúdio de inúmeras descobertas e avanços tecnológicos fundamentais; em particular, a descoberta dos neutrinos. No entanto, a sua total compreensão ainda é um mistério para a física de partículas. Entendidos como partículas fermiônicas fundamentais, os neutrinos possuem sua natureza desconhecida. Podendo ser diferentes de suas antipartículas, denominadas férmions de Dirac, ou também podendo ser as suas próprias antipartícula, sendo conhecidas como férmions de Majorana. Por outro lado, o valor de sua massa continua sendo um problema em aberto, supostamente relacionado à sua natureza. Portanto, é importante estudarmos modelos fenomenológicos viáveis para as duas naturezas possíves dos neutrinos. Além disso, é necessário procurar outros processos físicos cujos resultados experimentais sejam distintos de acordo com a natureza do neutrino. Um método bastante difícil, mas promissor, corresponde à detecção do fundo de neutrinos cósmicos, isto é, os neutrinos relíquia do Big Bang. Análises prévias mostraram que as taxas de detecção para neutrinos de Dirac e de Majorana resultam em valores distintos. Porém, este resultado foi obtido supondo como base o Modelo Padrão; assim, é crucial entender as possíveis consequências da existência de interações desconhecidas na detecção dos neutrinos da radiação cósmica de fundo. Outra relíquia notável prevista pela Cosmologia é a desconhecida Matéria Escura, que compõe ~25% do Universo. Todas as buscas por WIMPs (do inglês Weakly Interactive Massive Particles), um dos principais candidatos a Matéria Escura, tem dado resultados negativos. Isto tem forçado a criação de experimentos cada vez mais sensíveis. Contudo, os neutrinos poderão ser um obstáculo nessas buscas experimentais, pois estes convertir-se-ão em um fundo irredutível. Na presente tese, abordaremos estes três fenômenos diferentes, modelos de massa para os neutrinos, a detecção do fundo de neutrinos cósmicos e o fundo de neutrinos em experimentos de detecção direta de Matéria Escura, considerando as distintas características em cada caso. No estudo dos modelos de massa para os neutrinos consideraremos modelos para neutrinos de Majorana e Dirac; exploraremos modelos neutrinofílicos com dois dubletos de Higgs. Enquanto à detecção dos neutrinos relíquia, analisaremos as consequências da presença de física além do Modelo Padrão na taxa de captura pelo trítio. Finalmente, examinaremos o impacto dos neutrinos em experimentos de detecção direta de WIMPs, supondo as interações do Modelo Padrão junto com interações adicionais na forma de modelos simplificados.
243

Rekonstruktion der Energie von Myonen mit dem Baikal-Neutrinoteleskop NT-96

Streicher, Ole 04 May 2001 (has links)
Diese Arbeit beschreibt die Entwicklung einer Methode zur Energierekonstruktion von Myonen in Unterwasserteleskopen unter Verwendung der Amplituden und Trefferwahrscheinlichkeiten der Photomultiplier. Die Methode wird auf die Daten des Myon- und Neutrinoteleskopes NT-96 angewandt. / This thesis describes the development of a method for energy reconstruction of muons which are detected in underwater elescopes using the amplitudes and hit patterns of the photo multipliers. The method is applied to the data of the Baikal NT-96 muon and neutrino telescope.
244

Tomography of the Earth by Geo-Neutrino Emission / Tomografia da Terra pela emissão de geo-neutrinos

Tavares, Leonardo Estêvão Schendes 05 August 2014 (has links)
Geo-neutrinos are electronic anti-neutrinos originated from the beta decay process of some few elements in the decay chains of $^Th$ and $^U$ present in Earth\'s interior. Recent experimental measurements of these particles have been generating great expectations towards a new way for investigating directly the interior of the planet. It is a new multidisciplinary area, which might in the near future bring considerable clues about Earth\'s thermal dynamics and formation processes. In this work, we construct an inferential model based on the multigrid priors method to deal, in a generic way, with the geo-neutrino source reconstruction problem. It is an inverse problem; given a region in space V and a finite and small number of measurements of the potential generated on the surface of V by some charge distribution $ho$, we try to infer $ho$. We present examples of applications and analysis of models in two and three dimensions and we also comment how other a priori information may be included. Furthermore, we indicate the steps for inferring the best locations for future detectors. The objective is to maximize the amount of information liable to be obtained from experimental measurements. We resort to an entropic method of inference which may be applied right after the results of the multigrid method are obtained. / Geo-neutrinos são neutrinos provindos do decaimento beta de alguns poucos elementos nas cadeias de $^$Th e $^$U presentes no interior da Terra. Recentes medidas experimentais dessas partículas têm proporcionado grandes expectativas como uma nova maneira de se investigar o interior do planeta diretamente. Trata-se de uma área multidisciplinar nova, que poderá no futuro próximo nos trazer grandes esclarecimentos sobre a dinâmica térmica e o processo de formação da Terra. Neste trabalho, construímos um modelo de inferência baseado no método de multigrid de priors para tratar, de modo genérico, o problema da reconstrução das fontes de geo-neutrinos no interior da Terra. Trata-se de um problema inverso; dada uma região do espaço V e um número finito e pequeno de medidas do potencial gerado na superfície de V por uma distribuição de carga $ho$, tentamos inferir $ho$. Apresentamos exemplos de aplicações e análises do método em modelos bidimensionais e tridimensionais e também comentamos como outras informações a priori podem ser incorporadas. Além disso, indicamos os passos para se inferir onde detectores futuros devem ser posicionados. O objetivo é maximizar a informação passível de ser obtida das medidas experimentais. Utilizamos um método baseado em inferência entrópica e que pode ser aplicado diretamente depois que os resultados do método de multigrid são obtidos.
245

Soluções de grande comprimento de oscilação para o problema de neutrinos solares / Solutions of large length of oscillation for the solar neutrinos problem

Medina, Alberto Martin Gago 27 March 2001 (has links)
Esta tese apresenta uma análise estatística detalhada dos dados de experimentos com neutrinos solares mais recentes, com duas diferentes soluções para oscilações de neutrinos, ambas caracterizadas por um grande comprimento de oscilação. A primeira baseada no mecanismo de oscilação padrão, ou seja, induzida por massa, sendo esta estudada nos casos de duas e três gerações e dentro do regime de quase-vácuo. E a segunda, uma exótica, que usa como mecanismo de oscilação uma possível violação do princípio de equivalência, que foi analisada somente para o caso de duas gerações, sendo este discutido para transições entre neutrinos ativos, e entre neutrinos ativos e estéreis. Nossos resultados mostraram que ambas soluções são consistentes com os dados de neutrinos solares e, também, no caso específico do quase-vácuo, observamos que a hipótese de três gerações ficou desfavorecida. / This thesis presents a well detailed statistical analysis using the recent data from solar neutrino experiments. This analysis was done in the framework of two different solutions of neutrino oscillations, both characterized by a long oscillation wavelength. The first was based on the standard mass induced oscillation mechanism, here we worked in the scheme of two and three neutrino generations within the quasivacuum regime. The second was an exotic mechanism, where the neutrino oscillation is due to a possible breakdown of the equivalence principle, this alternative was analyzed only for two neutrino generations, in the cases for the conversion among active neutrino and active to sterile neutrino. Our results show a good agreement between the solar neutrino data and both solutions, also in the specific case of quasivacuum, we found that the hypothesis for the three neutrino generation is disfavored.
246

Study of the cosmic muon-induced background for the theta 13 angle in the Double Chooz neutrino oscillation experiment / Étude du bruit de fond d'origine cosmique pour la mesure de l'angle de mélange theta 13 au sein de l'expérience Double Chooz

Kale Sayi, Kenny 09 July 2018 (has links)
L’expérience Double Chooz, située sur le site de la centrale nucléaire de Chooz dans la région des Ardennes en France, étudie la disparition des antineutrinos. Le but principal de l’expérience est de mesurer avec une grande précision l’amplitude d’oscillation sin2 2θ13 des antineutrinos émis par les deux réacteurs de la centrale de Chooz. La précision de cette mesure dépend fortement d’une connaissance précise des taux et de la forme des spectres des bruits de fond qui contaminent la sélection finale des antineutrinos en particulier dans la gamme d’énergie où l’oscillation des neutrinos est attendue. Nous avons étudié dans la présente thèse le bruit de fond d’origine cosmique dans l’expérience Double Chooz. En effet, les muons cosmiques traversant les détecteurs ou interagissant dans le voisinage immédiat sont la principale source de bruit de fond observés dans l’expérience Double Chooz. Deux types de bruits de fonds sont analysés et présentes dans cette thèse : les neutrons rapides (FN) et la double capture de neutrons (DnC). Des techniques d’identification dédiées ont été développées pour chacun de ces bruits de fond et, par conséquent, les formes spectrales et les taux associés ont été́ déterminés. Les valeurs obtenues dans le cadre de ce travail servent de paramètres d’entrée dans le fit final d’où la valeur de θ13 est extraite. La dernière mesure publiée par la collaboration Double Chooz est sin2 2θ13 = 0.119 ± 0.016. / The Double Chooz experiment is- a reactor antineutrino disappearance experiment located on the site of the Chooz nuclear power plant in the Ardennes region in France. The principal aim of the experiment is a high precision measurement of the oscillation amplitude sin2 2θ13 of the antineutrinos emitted from the two reactor cores of the Chooz power plant. The robustness and accuracy of this measurement depends strongly on a precise knowledge of the rates and spectral shapes of the backgrounds that contaminate the antineutrinos selection over the neutrino oscillation expected region. We have studied in the present thesis the muon induced background in the Double Chooz experiment. Indeed, cosmic muons crossing the detectors or interacting in the neighborhood constitute the main source of background events encountered in Double Chooz. Two distinct backgrounds analysis are presented in this thesis: fast neutrons (FN) and double capture of neutrons (DnC). Dedicated identification techniques have been developed for each of these backgrounds and, consequently, the associated spectral shapes and rates have been determined. The values obtained in this work serve as inputs in the final fit whence the θ13 value is extracted.The latest measurement released by the Double Chooz collaboration is sin2 2θ13 = 0.119 ± 0.016$.
247

Testing non-standard neutrino interactions from 8B solar neutrino rate measurement with Borexino to characterization of the 144Ce source of the SOX experiment. / Etude de propriétés non standard du neutrino avec Borexino : mesure du taux de 8B solaire et caractérisation de la source de 144Ce pour tester l'hypothèse stérile dans l'expérience SOX

Houdy, Thibaut 18 September 2017 (has links)
Le détecteur Borexino, situé au laboratoire souterrain du Gran Sasso (LNGS), mesure les neutrinos solaires depuis 10 ans. Parmi les neutrinos solaires, le spectre continu du 8B jusqu’à 17 MeV permet de tester la zone de transition de l’effet de résonance dans la matière dit effet MSW. Cette nouvelle analyse augmente d’un ordre de grandeur la statistique par rapport à la précédente mesure de Borexino publiée en 2011. Pour ce faire, l’ensemble du volume scintillant a été inclus dans l’analyse, aucune coupure géométrique n’ayant été effectué au dessus de 5 MeV. Cela a permis l’identification d’un nouveau bruit de fond non pris en compte précédemment. L’ensemble des bruits de fond au dessus de 3 MeV est maintenant compris et la composante neutrino peut-être extraite d’un fit radial du détecteur. Afin de tester l’existence d’un neutrino stérile léger, une source de 3-5,5 PBq de 144Ce sera installée sous Borexino au début de l’année 2018 pour un an et demi de prise de données : c’est l’expérience CeSOX. Cette source est produite par PA MAYAK par purification de combustible nucléaire usagé, par conséquent les potentiels contaminants radioactifs sont très nombreux et peu contraints. Pour tester l’hypothèse stérile, une mesure en flux, une mesure en forme et une mesure combinée seront effectuées dans l’ensemble du détecteur Borexino. Ces mesures sont fortement dépendantes de la connaissance intime de la source (composition, forme du spectre beta du 144Ce, énergie moyenne 144Ce et 144Pr). A cette fin, un spectromètre gamma a été spécifiquement étalonné et entièrement simulé au CEA, Saclay. De même un spectromètre beta a été dessiné, assemblé, simulé et est en cours d’étalonnage. Finalement, des mesures de spectrométrie alpha et de masse seront réalisés sur des échantillons représentatifs envoyés au CEA, Saclay afin de contraindre au mieux la composition de la source de 144Ce de SOX. / Located in the Gran Sasso underground laboratory (LNGS), Borexino measures solar neutrinos for 10 years. Among solar neutrinos, 8B continuous spectrum (up to 17 MeV) enables to test the transition zone between vacuum and matter regime of the MSW effect. This new measurement increases by one order of magnitude the exposure with respect to previous Borexino publication. To do so, the entire active volume is considered in this analysis above 5 MeV. A new background has been identified and a radial fit is done above 3 and 5 MeV enabling to extract the neutrino component. Existence of a light sterile neutrino would have important consequences on astrophysics and cosmology. SOX is the only experiment aiming at testing this hypothesis using a punctual radioactive source. A 3-5.5 PBq 144Ce source is actually under production and will be positioned under Borexino in 2018. Precise knowledge of the source is one of the main challenge of this experiment, based on rate and shape neutrino measurement. Two critical parameters are the heat released by the source for activity measurement and the expected neutrino spectrum in the detector. We first describe the SOX experiment insisting on 144Ce source production. Then, we focus on Saclay installations dedicated to constrain radioactive contamination inside the source using representative samples. Alpha, gamma and mass spectroscopy calibration and simulation are discussed and competitive constrains are derived. A status on 144Ce beta shape measurements is done as well as presentation of future measurement.
248

Characterizing cosmic neutrino sources

Mohrmann, Lars 30 November 2015 (has links)
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)%.
249

Mesures de la section efficace de la réaction $^7$Be(p,$\gamma)^8$B à basse énergie et implications dans le problème des neutrinos solaires

Hammache, Fairouz 07 July 1999 (has links) (PDF)
LE 8B PRODUIT DANS LE COEUR DU SOLEIL A TRAVERS LA REACTION 7BE(P,) 8B EST LA SOURCE MAJEURE SINON UNIQUE DES NEUTRINOS DE HAUTES ENERGIES DETECTES DANS LA PLUPART DES EXPERIENCES DE DETECTION DES NEUTRINOS SOLAIRES, EXCEPTE GALLEX ET SAGE. CES EXPERIENCES ONT TOUTES MESURE UN FLUX DE NEUTRINOS INFERIEUR A CELUI PREDIT PAR LES MODELES SOLAIRES. PLUSIEURS EXPLICATIONS ONT ALORS ETE INVOQUEES POUR TENTER DE COMPRENDRE CE DEFICIT MAIS TOUTES NECESSITENT UNE CONNAISSANCE PRECISE DE LA VALEUR DE LA SECTION EFFICACE DE LA REACTION 7BE(P,) 8B, PUISQUE LE FLUX DES NEUTRINOS DU 8B EST DIRECTEMENT PROPORTIONNEL A CETTE DERNIERE. LA MESURE DIRECTE DE LA SECTION EFFICACE DE CETTE REACTION A L'ENERGIE SOLAIRE EST IMPOSSIBLE A CAUSE DE SA TRES FAIBLE VALEUR (DE L'ORDRE DU FEMTOBARN). POUR CONTOURNER CE PROBLEME, LES SECTIONS EFFICACES SONT MESUREES A PLUS HAUTE ENERGIE PUIS EXTRAPOLEES A L'ENERGIE SOLAIRE EN UTILISANT UNE DEPENDANCE EN ENERGIE THEORIQUE. LES SIX DETERMINATIONS EXPERIMENTALES PRECEDENTES DE LA SECTION EFFICACE SE DIVISAIENT EN DEUX GROUPES BIEN DISTINCTS PRESENTANT DES ECARTS DE L'ORDRE DE 30%, CE QUI IMPLIQUAIT UNE INCERTITUDE DU MEME ORDRE SUR LE FLUX DES NEUTRINOS DE HAUTES ENERGIES. REMESURER AVEC UNE MEILLEURE PRECISION LA SECTION EFFICACE DE CETTE REACTION EST DONC APPARU TRES IMPORTANT. DANS UN PREMIER TEMPS, NOUS AVONS EFFECTUE DES MESURES DIRECTES DE LA SECTION EFFICACE DE CETTE REACTION DANS LA GAMME D'ENERGIE COMPRISE ENTRE 0.35 ET 1.4 MEV (CM). CES EXPERIENCES ONT FAIT L'OBJET D'UNE MESURE PRECISE DE CHACUN DES PARAMETRES INTERVENANT DANS LA DETERMINATION DE LA SECTION EFFICACE. DANS UN SECOND TEMPS, NOUS AVONS ENTREPRIS DES MESURES DE LA SECTION EFFICACE AUPRES DE L'ACCELERATEUR PAPAP, A 185.8 KEV, 134.7 KEV ET 111.7 KEV, L'ENERGIE DANS LE CENTRE DE MASSE LA PLUS BASSE JAMAIS ATTEINTE A CE JOUR. LES RESULTATS SONT EN EXCELLENT ACCORD AVEC CEUX OBTENUS A PLUS HAUTES ENERGIES. LA VALEUR TROUVEE POUR LE FACTEUR ASTROPHYSIQUE S 1 7(0), PAR L'EXTRAPOLATION DE NOS DONNEES EST EGALE A 19.21.3 EV-B, CE QUI ENTRAINE UNE REDUCTION SENSIBLE DE L'INCERTITUDE SUR LE FLUX DES NEUTRINOS DE HAUTE ENERGIE DU 8B.
250

Neutrino velocity measurement with the OPERA experiment in the CNGS beam

Brunetti, Giulia 20 May 2011 (has links) (PDF)
The thesis concerns the measurement of the neutrino velocity with the OPERA experiment in the CNGS beam. There are different theoretical models that allow for Lorentz violating effects which can be investigated with measurements on terrestrial neutrino beams. The MINOS experiment published in 2007 a measure on the muon neutrinos over a distance of 730 km finding a deviation with respect to the expected time of flight of 126 ns with a statistical error of 32 ns and a systematic error of 64 ns. The OPERA experiment observes as well muon neutrinos 730 km away from the source, with a sensitivity significantly better than MINOS thanks to the higher number of interactions in the detector due to the higher energy beam and the much more sophisticated timing system explicitly upgraded in view of the neutrino velocity measurement. This system is composed by atomic cesium clocks and GPS receivers operating in "common view mode". Thanks to this system a time-transfer between the two sites with a precision at the level of 1 ns is possible. Moreover, a Fast Waveform Digitizer was installed along the proton beam line at CERN in order to measure the internal time structure of the proton pulses that are sent to the CNGS target. The result on the neutrino velocity is the most precise measurement so far with terrestrial neutrino beams: the neutrino time of flight was determined with a statistical uncertainty of about 10 ns and a systematic uncertainty smaller than 20 ns.

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