Orientador: Fernando Luis de Campos carvalho / Banca: Julio Marny Hoff da Silva / Banca: José Abdalla Helayël-Neto / Resumo: O objetivo deste trabalho é estudar os aspectos gerais do setor escalar do Modelo Padrão, a partir princípio de gauge, que dá consistência teórica à formulação do Modelo Eletrofraco, assim como a quebra espontânea de simetria e o mecanismo de Higgs que são fundamentais no contexto do modelo para a geração de massa das partículas elementares e, tem como consequência o surgimento de uma nova partícula escalar massiva, o bóson de Higgs do Modelo Padrão, cuja massa não está definida no modelo. Apresentamos um estudo dos principais modos de produção e decaimento do bóson de Higgs bem como a sua busca em aceleradores. Apresentamos um conjunto de resultados experimentais que foram publicados ao longo dos anos nas principais colaborações como LEP, Tevatron e LHC, que contribuíram na longa trajetória da busca, até sua identificação em 2012 / Abstract: The objective of this work is to study the general aspects of the scale sector of the Standard Model the principle of gauge, which gives theoretical consistency to the electroweak model formulation, as well as spontaneous symmetry breaking and the Higgs mechanism, that are fundamental for the mass generation of the elementary particles, and gives rise to a new massive particle scale, the Higgs boson of whose value is not defined in the model. We present a study of the major modes of production and decay of Higgs boson as well as search of such particle in accelerators. We present a set of experimental results that have been published over the years in the major collaborations as LEP, Tevatron and LHC, which contributed in the long history of the Higgs boson search, until its identification in 2012 / Mestre

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-06-22T12:43:46Z No. of bitstreams: 0 / Made available in DSpace on 2016-06-22T12:43:46Z (GMT). No. of bitstreams: 0 / Neste trabalho foi estabelecido um sistema padrão primário para raios X de energias baixas (10 kV a 50 kV), utilizando uma câmara de ionização de ar livre de cilindros concêntricos da marca Victoreen (modelo 481-5) no Laboratório de Calibração de Instrumentos (LCI) do Instituto de Pesquisas Energéticas e Nucleares (IPEN/CNEN-SP). Para isso foi desenvolvido um novo protocolo de alinhamento da câmara de ionização no sistema de radiação e foi feita uma modificação no suporte dos micrômetros utilizados para o movimento dos cilindros internos. Os resultados obtidos nos testes de estabilidade e de caracterização ficaram dentro dos limites estabelecidos pelas normas IEC 61674 e IEC 60731. Foram determinados também os fatores de correção para atenuação de fótons no ar, transmissão e espalhamento no diafragma, espalhamento e fluorescência, e recombinação iônica. Esses valores foram comparados com os valores obtidos pelo laboratório padrão primário alemão,Physikalisch-Technische Bundesanstalt (PTB), mostrando boa concordância. Por último, foi determinado o valor absoluto da grandeza taxa de kerma no ar para as qualidades padronizadas de mamografia de feixes diretos WMV28 e WMV35 e feixes atenuados WMH28 e WMH35; os resultados são compatíveis, com diferença máxima de 3,8% com os valores obtidos utilizando o sistema padrão secundário do LCI. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

This PhD dissertation presents the measurement of the cross section of jet production in association with a Z boson in proton-proton collisions at the Large Hadron Collider in CERN, with a center-of-mass energy of 8 TeV in 2012 and of 13 TeV in 2015. The data used for this analysis were collected by the Compact Muon Solenoid (CMS) detector, with an integrated luminosity of 19.6 fb-1 in 2012 and of 2.25 fb-1 in 2015. The differential cross section is measured as a function of jet multiplicity, jet transverse momentum and rapidity, and the scalar sum of jet transverse momenta. The rapidity correlations between the Z boson and jets are also measured benefiting from the large statistics of data taken in 2012. All distributions of measured observables are obtained after correcting detector effects using unfolding approach, and the results of two leptonic decaying channels of Z boson are combined. Coming along with the systematic and statistical uncertainties, the measurement is compared to different theoretical predictions at different accuracy levels. The predictions are from MADGRAPH 5, SHERPA 2 (for 8 TeV analysis only), MADGRAPH_AMC@NLO, and fixed next-to-next-to-leading order (for 13 TeV analysis only). Thanks to the unprecedented high energy and the large statistics of data, precision measurement is accomplished in a physical phase space never reached before. This measurement provides precise systematics for different theoretical models. It also quantifies the improvement with higher order of perturbative quantum chromodynamics calculations on matrix elements relative to the leading order multi-leg approach. In particular to the rapidity correlation study, new matching schemes (FxFx and MEPS@NLO) for next-to-leading order matrix elements and parton shower show significant improvements with respect to the MLM matching scheme for leading order multi-leg matrix elements and parton shower. This measurement also gives precise background estimation for the measurements of many other processes in Standard Model like top quark production and gauge boson couplings, and for new physics searches such as Supersymmetry. In this thesis, the jet energy correction and calibration for the high level trigger system of CMS are also depicted. From 2012 to 2015, the Large Hadron Collider was upgraded, not only with the center-of-mass energy of the beams enlarged, but also with the instantaneous luminosity increased. The time distance between two particle bunches in a beam is reduced. As a result, the reconstructed momenta of the jets produced in each bunch crossing are significantly contaminated by multiple interactions. A dedicated technical approach has been developed for correcting the reconstructed jet momenta. The corrections have been calibrated and configured for the data taking in 2015 and 2016. / Cette thèse présente une mesure de la section efficace de production de jets associés à un boson Z dans les collisions proton-proton du Grand Collisionneur de Hadron (LHC) situé au CERN, avec des énergies dans le centre de masse de 8 TeV et 13 TeV, respectivement pour les années 2012 et 2015. Les données utilisées pour cette analyse ont été collectées par le détecteur Compact Muon Solenoid (CMS). Elles constituent des échantillons de luminosités intégrées de 19.6 fb⁻¹ et 2.25 fb⁻¹, respectivement pour 2012 et 2015. Nous mesurons la section efficace différentielle en fonction de la multiplicité de jets, de l’impulsion transverse et de la rapidité des jets, et en fonction de la somme scalaire des impulsions transverses des jets. La corrélation entre les rapidités du boson Z et des jets est aussi mesurée et bénéficie de la large statistique prise en 2012. Toutes les distributions d’observables mesurées sont obtenues après corrections pour les effets détecteurs et les résultats des canaux de désintégration muonique et électronique du boson Z sont combinés. Tenant compte des incertitudes statistiques et systématiques, les mesures sont comparées à différentes prédictions théoriques ayant différents niveaux de précision. Les prédictions sont obtenues de MADGRAPH 5, SHERPA 2 (pour l’analyse à 8 TeV uniquement), MADGRAPH_AMC@NLO, et un modèle fixé au NNLO (pour l’analyse à 13 TeV uniquement). Par ces mesures de précisions, et en particulier celle de la corrélation de rapidités, nous avons acquis une compréhension plus approfondie de la chromodynamique quantique dans son régime perturbatif. Grâce à la plus haute énergie jamais atteinte en laboratoire, et à la grande statistique disponible, nous avons sondé avec précision des endroits de l’espace des phases jusque là inaccessibles.Dans cette thèse, les corrections et la calibration de l’énergie des jets pour le haut niveau de sélection de CMS est également présentée. Durant la période de 2012 à 2015, le LHC a été amélioré, non seulement l’énergie dans le centre de masse a augmenté, mais la luminosité instantanée a aussi été amplifiée. L’écart temporelle entre deux paquets de particules dans les faisceaux du LHC a été réduite. L’une des conséquences est que l’impulsion reconstruite pour les jets produits lors d’un croisement de faisceau à une contribution significative venant des multiples interactions ayant lieux lors du croisement des paquets. Une approche technique dédiée a été développée pour corriger l'impulsion des jets. Les corrections obtenues ont été calibrées aux données prises en 2015 et 2016. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

In the first part of the thesis, the need for physics beyond the Standard Model, as attested to by the evidence of dark matter, motivates us to study the effects of introducing into the standard theory of Leptogenesis a hidden sector scalar coupled to the Standard Model through the Higgs portal. We find that the new interactions are not constrained by the Davidson-Ibarra bound, thus allowing us to lower the mass scale of Leptogenesis into the TeV range, accessible to experiments. We then consider a broader class of new physics models below the electroweak scale, and classify precision observables according to whether or not deviations from the Standard Model at current levels of sensitivity can be explained purely in terms of new light degrees of freedom. We find that hadronic precision observables, e.g. those that test fundamental symmetries such as electric dipole moments, are unambiguous pointers to new UV physics. In the second part of the thesis, motivated by recent measurements of the spatial structure of impurities embedded in superconductors (SC), we study the effect of superconductivity on impurity states by generalizing the Anderson model of a quantum s-wave impurity to include orbital degeneracy. We find that the proximity effect induces an electron-electron attractive potential on the impurity site that mirrors the BCS pairing mechanism, resulting in the appearance of atomic Cooper pairs within the superconducting energy gap, called Yu-Shiba-Rusinov (YSR) states. We find that electron orbital degeneracy allows YSR states to have non-trivial orbital quantum numbers thus opening the possibility for optical transitions among YSR states. We enumerate the one-photon selection rules that apply to YSR states, unveiling transitions to the vacuum state that are forbidden in the normal state. / Graduate

The Large Hadron Collider is the most powerful particle accelerator built to date. It is a proton-proton and heavy ion collider which in 2015 and 2016 operated at an unprecedented center of mass energy of √s = 13 TeV. The Tile Calorimeter is the ATLAS hadronic calorimeter covering the central region of the detector. It is designed to measure hadrons, jets, tau particles and missing energy. In order to accurately be able to properly reconstruct these physical objects a careful description of the electronic noise is required. This thesis presents the work done in updating, monitoring and studying the noise calibration constants used in the processing and identication of hadronic jet in the 2011 data. Moreover the results of the searches for compressed supersymmetric squark-neutralino and large extra dimensions models are also presented in this thesis. The present work uses an experimental signature with a high energy hadronic jet and large missing transverse energy later often referred to as monojet signature. The search for supersymmetry is carried out using an integrated luminosity of 3.2 fb-1 recorded by the ATLAS experiment in 2015. The search for large extra dimensions presented in this work uses the full 2015 + 2016 dataset of 36.1 fb-1. No signicant excess compared to the Standard Model prediction has been observed on the production of squark pairs with the subsequent decay of the squark in a quark and a neutrino. Exclusion limits are set on squark production as a function of the neutralino mass. Squark masses up to 608 GeV are excluded for a mass difference between the squark and the neutralino of 5 GeV. In the second search for the presence of large extra spatial dimensions in the Arkani-Hamed, Dimopoulos and Dvali model scenario a good agreement between data and Standard Model prediction is observed and exclusion limits are set on the effective Planck scale MD of 7.7 and 4.8 TeV for two and six hypothesized large extra dimensions respectively signicantly improving earlier results.

Orientador: Marcelo Moraes Guzzo / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T10:36:59Z (GMT). No. of bitstreams: 1 Ferreira_CesarPeixoto_M.pdf: 5430137 bytes, checksum: 52b53b619a2021426f948ae3c70beb98 (MD5) Previous issue date: 2014 / Resumo: Neste trabalho analisa-se uma das extensões do Modelo Padrão das Partículas Elementares, conhecida como Extensão 3-3-1\', e suas aplicações a Cosmologia. Esta classe de modelos constitui uma das mais enxutas extensões do Modelo Padrão, e possui entre as suas qualidades respostas a problemas deixados em aberto dentro do Modelo Padrão. Entre estes, lista-se o problema do numero de gerações e o problema da assimetria das massas dos quarks, respondidos através de um critério de consistência interna do modelo, a saber, o cancelamento das anomalias quirais. O modelo especifico escolhido para estudo foi o Modelo 3-3-1 com neutrinos de m~ao direita (3-3-1RH), e todas as suas principais características são analisadas. Para aplicações a Cosmologia, o 3-3-1 foi analisado em suas aplicações ao problema da Matéria Escura. Neste caso, analisar-se-~ao candidatos a Matéria Escura em uma extensão do 3-3-1, chamada Modelo 3-3-1 Left-Right (3L3R). Estes candidatos s~ao neutrinos estereis de massa na escala keV, e a eles s~ao aplicados os limites cosmológicos impostos por Decaimento em Raio-X, Neff e Abundância de matéria escura. 3 casos foram analisados: (1) Desacoplamento dos neutrinos estereis anterior a aniquilação dos múons. (2) Desacoplamento anterior a aniquilação dos pons; (3) Desacoplamento anterior a Hadronização. A aplicação dos limites supracitados revelou que estes neutrinos n~ao sofrem de restrições de decaimentos em Raio-X. Para cada um dos 3 casos, o valor de Neff por neutrino estéril foi de 3.69, 3.53 e 3.09, respectivamente. Como experimentalmente, Neff = 3:280:28, conclui-se que em 2 dos casos, apenas 1 neutrino novo e admitido, e no caso restante os 3 neutrinos novos do 3L3R s~ao possíveis. Por m, o calculo de abundância revelou um excesso destes neutrinos, usando-se o método para calculo de abundância de neutrinos ativos. A abundância calculada e maior que a medida experimentalmente em todos os casos posseis para o modelo, mesmo considerando-se um caso limite. Dessa forma, conclui-se que algum mecanismo alternativo de diluição de densidade destes neutrinos e necessário / Abstract: In this dissertation, one of the extensions of the Standard Model of Elementary Particles(SM), known as the '3-3-1 Extension\', and its aplication to Cosmology are analysed. This class of models constitutes one of the most economical extensions of the Standard Model, and have among its qualities answers to open problems within the SM. Among them, we mention the generation problem and the quark mass assymetry problem. Both of these problems are answered trough the use of a internal consistency criterion of the model: The cancelation of chiral anomalies. The model chosen for study was the 3-3-1 Model with right handed neutrinos (3- 3-1RH), and all its main caracteristics are analysed. To aplications to Cosmology, the 3-3-1 was studied within the Dark Matter problem. In this case, we analyse dark matter candidates in one extension of the 3-3-1, known as the Left-Right 3- 3-1 Model (3L3R). These candidates are sterile neutrinos with keV masses, and to them cosmological limits are applied. These limits are the decays into X-Rays, Neff and Dark Matter Abundance. 3 cases were analysed: (1) Decoupling of the sterile neutrinos before muon annihilation; (2) Decoupling before pion annihilation; (3) Decoupling before Hadronization. The application of the limits mentioned above revealed that these neutrinos do not, at the moment, have any restrictions coming from decays into X-Rays, because this kind of decay is forbidden in the 3L3R. For each of the 3 cases, Neff had the value of 3.69, 3.53 e 3.09, respectively. When this is compared with the experimental value, Neff = 3:28 0:28, we conclude that in two cases, only one sterile neutrino is roughly allowed. In the remaining case, all 3 new neutrinos of the 3L3R are possible. The calculation of abundance revelead an excess of these neutrinos, using the method that is used to calculate abundance of active neutrinos. The calculated abundance is bigger than the experimentally determined in all possible cases, even when we consider a limit case. We conclude that some alternative mechanism for density dilution is necessary / Mestrado / Física / Mestre em Física

Le LHC, qui est le collisionneur proton-proton le plus puissant du monde situé au CERN (Suisse), donne une occasion unique de pouvoir tester nos connaissances des interactions fondamentales à l'échelle du TeV. Au cours de cette thèse, deux projets ont été accomplis dans ce but. Tout d'abord, la mesure de la section efficace de production d'au moins deux photons dans l'état final (pp→γγ+X) a été réalisée à l'aide des données prises avec une énergie dans le centre de masse de 8 TeV par le détecteur ATLAS, qui est l'un des détecteurs polyvalents installé autour du LHC. Les photons sont des particules intéressantes pour tester la théorie de l'interaction forte (chromodynamique quantique ou QCD) car ils sont couplés aux quarks et aux gluons sans pour autant s'hadroniser, ce qui permet de pouvoir les mesurer avec une très bonne résolution. La mesure de leur taux de production au LHC permet de tester la QCD à la fois dans le domaine perturbatif et non-perturbatif. Elle est également sensible à l'émission de particules à basse énergie dans l'état initial, qui est un phénomène délicat à décrire d'un point de vue théorique à cause des divergences molles et collinéaires découlant de la QCD. Les incertitudes expérimentales ont été divisées par un facteur 2 ou plus comparé aux mesures réalisées précédemment au LHC ou au Tevatron (Fermilab, États-Unis) et la très bonne statistique des données d'ATLAS à 8 TeV a permis une augmentation significative à la fois de la résolution et de la portée de la mesure. En général, un bon accord est observé avec les prédictions théoriques. Le second projet réalisé au cours de la thèse est consacré à l'évaluation du potentiel de découverte relié à la mesure de la diffusion γγ au LHC (γγ→γγ). La diffusion γγ est un processus singulier car prédit uniquement via des fluctuations quantiques qui n'a jamais été observé directement. Il implique un terme de couplage à quatre photons, qui montre une sensibilité significative à une large gamme de modèles d'extension du modèle standard à haute énergie, tels que ceux prédisant l'existence de dimensions supplémentaires de l'espace pour résoudre le problème de hiérarchie. En tirant profit du flux important de photons venant des protons au LHC, je montre qu'il est possible de découvrir des couplages anomaux à quatre photons avec une sensibilité permettant de rivaliser avec certaines recherches directes. Enfin, j'ai eu l'occasion de tester la nouvelle puce SAMPIC qui vise à réaliser des mesures de temps de vol avec une précision de l'ordre de quelques picosecondes grâce à un échantillonnage rapide des signaux de détecteur. Les performances de SAMPIC ont été testées à partir de signaux gaussiens produits par un générateur et par des détecteurs soumis à des impulsions infrarouges. Dans ces conditions idéales, SAMPIC permet de réaliser des mesures de temps de vol avec une résolution de l'ordre de 4 (40) ps pour les signaux générés (de détecteurs). / The LHC, which is the most powerful proton-proton collider in the world located at CERN (Switzerland), brings unprecedented opportunities to test our knowledge of the fundamental interactions at the TeV scale. In this work, two main projects have been achieved for this purpose. First, the production cross section measurement of at least two photons in the final state (pp→γγ+X) is performed with data taken at a center-of-mass energy of 8 TeV by the ATLAS detector, which is one of the multipurpose detector installed around the LHC ring. Photons are interesting probes to test the theory of strong interactions (Quantum chromodynamics or QCD) since they couple significantly to quarks and gluons but do not hadronize and thus still allow to perform high resolution measurements. The measurement of their production rate at the LHC allows to test QCD in both the perturbative and the non-perturbative domain. It is also sensitive to the emission of soft particles in the initial-state, which is tricky to handle on the theory side due to the collinear and soft divergences arising in QCD. Experimental uncertainties have been reduced by a factor 2 or more with respect to the measurements performed previously at the LHC or at the Tevatron (Fermilab, USA) and the high statistics of the ATLAS data sample at 8 TeV allows to increase significantly both the reach and the resolution of the measurement. In general, a good agreement is observed with theoretical predictions. The second project achieved in this work is dedicated to the evaluation of the light-by-light scattering potential (LbyL, γγ→γγ) for new physics searches. LbyL is an intriguing process arising from quantum fluctuations only that has never been observed directly. It involves four-photon couplings, which are shown to be highly sensitive to a broad range of new physics models at high energy such as the ones predicting the existence of extra spatial dimensions to solve the hierarchy problem currently affecting the standard model of particle physics. By taking benefit of the photon flux from the protons at the LHC, I show that one may discover anomalous four photon couplings with a sensitivity allowing to compete with several direct new physics searches. Finally, I had the opportunity to test the new SAMPIC chip which aims to perform time-of-flight measurements with a few picoseconds precision from fast samplings of detector signals. SAMPIC timing capabilities have been tested using Gaussian signals generated by a signal generator or by silicon detectors pulsed with an infrared laser. Under these ideal conditions, the SAMPIC chip has proven to be capable of timing resolutions down to 4 (40) ps with synthesized (silicon detector) signals.

Une recherche de résonance neutre et lourde X est effectuée dans le canal X→WW→eνμν en utilisant les données en collision pp correspondant à une luminosité intégrée d'environ 36,1 fb⁻¹, prises à une énergie dans le centre-de-masse de 13 TeV par le détecteur ATLAS au LHC. La résonance peut être soit un boson de Higgs scalaire lourd soit d'autres résonances lourdes aux spins différents. Deux scénarios de largeur sont étudiés pour un boson de Higgs lourd dans les modes de fusion gluon-gluon et de fusion vecteur-boson; une largeur soit étroite soit grande. Plusieurs hypothèses sont utilisées pour rechercher d'autres résonances, comme le modèle avec deux doublets de Higgs, le modèle de Georgi-Machacek, le modèle avec un triplet vectoriel en mode d'annihilation quark-antiquark, le modèle de Randall-Sundrum avec un graviton de spin 2 correspondant à un paramètre d'échelle de courbure de 1 ou 0,5 et un signal de spin 2 dans le mode de fusion vecteur-boson. Trois catégories d'événements indépendantes sont définies dans l'analyse : une catégorie inclusive où les espaces de phase en fusion vecteur boson sont exclus et deux autres catégories qui sont optimisées pour les signaux produits en mode de fusion vecteur-boson avec un jet ou au moins deux jets. Aucun excès significatif d'événements au-delà de la prédiction du bruit de fond du Modèle Standard ne se trouve dans la gamme de masse comprise entre 200 GeV et 5 TeV. Les limites supérieures sont obtenues sur le produit de la section efficace de la production de la résonance et du rapport de branchement X→WW. Pour les signaux de bosons de Higgs lourds, les valeurs supérieures à 6,4 pb et 1,3 pb à mH = 200 GeV et supérieures à 0,008 pb et 0,005 pb à 4 TeV sont exclues à un niveau de confiance de 95% pour la fusion gluon-gluon et la fusion vecteur-boson, respectivement. Pour les signaux prédits par le modèle avec un triplet vectoriel, les valeurs de masse inférieures à 1,3 TeV sont exclues. De la même manière, pour les signaux prédits par le modèle de Randall­ Sundrum, les valeurs de masse inférieures à 1,1 TeV et 850 GeV sont exclues pour le paramètre d'échelle de courbure de 1 et 0.5, respectivement. / A search for a heavy neutral resonance X is performed in the X→WW→eνμν decay channel using pp collision data corresponding to an integrated luminosity of 36.1 fb⁻¹, collected at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. The resonance can be either a heavy scalar Higgs boson or other heavy resonances with different spins. Two scenarios are considered for the heavy Higgs boson hypotheses with different decay widths in both the gluon-gluon fusion and the vector­ boson fusion production modes, namely a narrow-width approximation and a large width assumption. Several hypotheses are used for the interpretation to search for other resonances, like two Higgs doublet models, Georgi-Machacek model, heavy vector triplet model in the quark-antiquark annihilation mode, a bulk Randall-Sundrum graviton model with a spin-2 Graviton with a curvature scale parameter of either 1 or 0.5 and a spin-2 signal in the vector-boson fusion mode. Three orthogonal event categories are defined in the analysis: two vector-boson fusion categories which are optimised for the signals produced in the vector-boson fusion mode with one jet or at least two jets and one quasi-inclusive gluon-gluon fusion category where the vector boson fusion phase spaces defined by the two vector-boson fusion categories are excluded. No significant excess of events beyond the Standard Model background prediction is found in the mass range between 200 GeV and up to 5 TeV. Upper limits are set on the product of the production cross section of the resonance and the X→WW branching fraction. For heavy Higgs boson signals, values above 6.4 pb and 1.3 pb at 200 GeV and above 0.008 pb and 0.005 pb at 4 TeV are excluded at 95% confidence level for the gluon-gluon fusion and the vector-boson fusion production modes, respectively. For signals predicted by the heavy vector triplet model, mass values below 1.3 TeV are excluded. Similarly, for signals predicted by the bulk Randall-Sundrum graviton model, mass values below 1.1 TeV and 850 GeV are excluded for the curvature scale parameter of 1 and 0.5, respectively.

Die Arbeit beschäftigt sich mit Faltungsoperatoren auf Kegeln, die in Lebesgueräumen L^p(R^2) (1<p<\infty) von Funktionen auf der Ebene wirken. Es werden asymptotische Spektraleigenschaften der zugehörigen Finite Sections studiert. Im Falle p=2 (Hilbertraum) wird das Invertierbarkeitsproblem von Operatoren vom Faltungstyp auf Kegeln mit Hilfe der Methode der Standard-Modell-Algebren untersucht.

Not so long ago, the value of the branching ratio of a neutral pion decay to an electron-positron pair (π0 → e− e+ ) has been updated and became more accurate thanks to the fact, that new measurements were performed at KTeV experiment at Fermilab. In this context it has been showed, that the Standard Model theoretical prediction is not precise enough. The resulting discrepancy was not explained yet. In presented work, there are summarized preceding results, al- ready computed correction were taken into account and newly the Bremsstrahlung contribution was thoroughly calculated. Besides, the contribution of π-loop cor- rections in terms of double-logarithms is estimated. In the end, because of the persisting disagreement of the accepted theory with the experiment, an additional contribution is suggested from beyond the Standard Model on the basis of models describing the dark matter. The latter mentioned is a hot candidate to explain many phenomena, for example the mysterious source of a great amount of γ-rays coming from the center of our galaxy and having the origin in the annihilation of electron-positron pairs. 1