Thèses : « Particle Physics - Standard Model (SM) »

1

Glover, Brian Audley. « Topics in particle physics beyond the Standard Model ». W&M ScholarWorks, 2009. https://scholarworks.wm.edu/etd/1539623541.

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We present new models of particle physics beyond the Standard Model. These models include extensions to the ideas of extra dimensions, deconstruction, supersymmetry, and Higgsless electroweak symmetry breaking. Besides introducing new models and discussing their consequences, we also discuss how galaxy cluster surveys can be used to constrain new physics beyond the Standard Model.;We find that an ultraviolet completion of gauge theories in the Randall-Sundrum model can be found in a deconstructed theory. The warping of the extra dimension is reproduced in the low energy theory by considering a general potential for the link fields with translational invariance broken only by boundary terms. The mass spectrum for the gauge and link fields is found to deviate from the Randall-Sundrum case after the first couple modes. By extending this model to a supersymmetric theory space, we find that supersymmetry is broken by the generation of a cosmological constant. Unless the theory is coupled to gravity or messenger fields, the spectrum remains supersymmetric.;We also present a hybrid Randall-Sundrum model in which an infinite slice of warped space is added to the extra dimension of the original theory. The hybrid model has a continuous gravitational spectrum with resonances at the Kaluza-Klein excitations of the original orbifolded model. A similar model is considered where the infinite space is cutoff by the addition of a negative tension brane. SU(2)L x SU(2)R x U(1)B-L gauge fields are added to the bulk of our hybrid model and we find that electroweak symmetry is broken with an appropriate choice of boundary conditions. By varying the size of the extra dimension, we find that the S parameter can be decreased by as much as 60%.;Finally we review models of structure formation and discuss the possibility of constraining new physics with galaxy cluster surveys. We find that for a large scatter in the luminosity-temperature relation, the cosmological parameters favored by galaxy cluster counts from the 400 Square Degree ROSAT survey are in agreement with the values found in the WMAP-3 year analysis. We explain why X-Ray surveys of galaxy cluster number counts are insensitive to new physics that would produce a dimming mechanism.

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2

Setford, Jack. « Strongly coupled physics beyond the standard model ». Thesis, University of Sussex, 2018. http://sro.sussex.ac.uk/id/eprint/77429/.

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This thesis is concerned with strongly coupled extensions to the Standard Model. The majority of the thesis is dedicated to the study of Composite Higgs models, which are a proposed solution to the hierarchy problem of the electroweak scale. In these models the Higgs is a composite pseudo-Nambu Goldstone boson which forms a part of a new strongly interacting sector. There are many different variations on the basic Composite Higgs theme { the current status of some of these variations is assessed in light of results from the Large Hadron Collider. A new kind of Composite Higgs model is presented and studied, which features an alternative mechanism for the breaking of electroweak symmetry. A mechanism for deforming one model into another is also discussed, which might find application to the UV completion of Composite Higgs models. The formalism used in the Composite Higgs literature is also applied to the study of inflation, where the inflaton is assumed to be a pseudo-Nambu Goldstone boson arising from strongly coupled dynamics. A study of the inflaton potential is performed and its cosmological implications discussed. A different extension to the Standard Model with interesting phenomenological consequences is also studied. Quirks are strongly interacting particles whose masses are significantly higher than their confining scale. If produced in colliders, they leave unusual tracks which current searches are mostly blind to. A new search strategy for these hypothetical particles is proposed.

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Colburn, Russell J. III. « Beyond the Standard Model : Dark Matter and Collider Physics ». The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1507215920939059.

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4

Shaheen, Matloob H. « Neutral currents beyond the standard model ». Thesis, Durham University, 1988. http://etheses.dur.ac.uk/6334/.

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The electroweak standard model (Salam-Weinberg) is well-known to be a satisfactory and consistent theoretical description of all the experimental data we have obtained so far. In this thesis, we discuss possible phenomenology which goes beyond the standard model, with particular emphasis on the neutral current effects. First of all, the left-right symmetric extension of the standard model is discussed and we find limits on its parameters. We show that this model cannot explain certain newly reported and highly speculative events at the CERN collider [3], which in principle could be caused by the decay into two W's of a new heavy Z. We then discuss composite models where there is a strong expectation that there should be two neutral Z's of similar mass. We study the effects of these on neutral current phenomenology and show that in general the extra Z would be very hard to detect. A comparison of our model with a particular superstring model [6] is also made.

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Stephan, Christoph. « Noncommutative geometry and the standard model of particle physics ». Aix-Marseille 1, 2005. http://www.theses.fr/2005AIX11042.

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Alain Connes a découvert une approche algébrique à la géométrie en remplaçant la géométrie Riemannienne de spin ordinaire par des triplets spectraux. Un triplet spectral est un ensemble avec trois membres : une algèbre, un opérateur de Dirac et un espace de Hilbert. Toutes les informations géométriques de la variété sont codées dans les triplets spectraux. Une qualité nouvelle de cette reformulation est la possibilité d'inclure des espaces non commutatifs. Ils sont représentés par des algèbres non commutatives, alors que les espaces ordinaires sont codés par des algèbres commutatives. Il est maintenant possible de rendre les algèbres commutatives, qui représentent l'espace-temps, un petit peu non commutatives, en prenant le produit tensoriel avec une somme d'algèbres matricielles. Alain Connes et Ali Chamseddine ont découvert que, pour un certain choix d'algèbre matricielle, on obtient la relativité générale et la théorie de champ classique du modèle standard de la physique des particules. Les géométries presque-commutatifs offrent aussi une interprétation naturelle pour le boson de Higgs comme connexion dans la partie non commutative de la géométrie. Chaque triplet spectral presque-commutatif représente un modèle de Yang-Mills-Higgs et peut être un canditat potentiel pour une théorie physique. Dans cette thèse doctorale des restrictions physiques supplémentaires seront imposées sur les triplets spectraux, par exemple que les masses des fermions soient non-dégénérées et que la théorie soir renormalisable. A partir de ces principes fondamentaux tous les triplets spectraux presque-commutatifs ont été classifiés en collaboration avec les professeurs Thomas Schücker et Bruno Iochum, et avec Jan-Hendrik Jureit. Il est surprenant que le modèle standard de la physique des particules occupe une position proéminente dans cette classification. La question de savoir s'il y a des modèles physiques avec plus de quatre algèbres reste ouverte

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6

Conroy, Justin M. « Modifications of spacetime and particle physics beyond the standard model ». W&M ScholarWorks, 2005. https://scholarworks.wm.edu/etd/1539623481.

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In this dissertation we consider spacetime modifications that result in new physics beyond the standard model. We investigate various collider implications of a particular Lorentz-conserving formulation of QED in which spacetime coordinates are noncommuting. We also consider collider implications of Universal Extra Dimensions. Specifically, we address the possible formation of bound states involving the first quark KK-modes, i.e. KK-quarkonium. In addition, we consider the use of boundary conditions in extra dimensions to break gauge symmetries in unified theories. These boundary conditions can be related to a boundary Higgs sector that decouples from the theory. This technique of "Higgsless" symmetry breaking is applied to several models based on the trinified gauge group GT = SU(3)C x SU(3) L x SU(3)R. In addition, we analyze various phenomenological issues such as coupling unification and proton decay.

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7

Fok, Ricky. « Scenarios of Physics Beyond the Standard Model ». Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/11940.

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xviii, 124 p. : ill. (some col.)
This dissertation discusses three topics on scenarios beyond the Standard Model. Topic one is the effects from a fourth generation of quarks and leptons on electroweak baryogenesis in the early universe. The Standard Model is incapable of electroweak baryogenesis due to an insufficiently strong enough electroweak phase transition (EWPT) as well as insufficient CP violation. We show that the presence of heavy fourth generation fermions solves the first problem but requires additional bosons to be included to stabilize the electroweak vacuum. Introducing supersymmetric partners of the heavy fermions, we find that the EWPT can be made strong enough and new sources of CP violation are present. Topic two relates to the lepton avor problem in supersymmetry. In the Minimal Supersymmetric Standard Model (MSSM), the off-diagonal elements in the slepton mass matrix must be suppressed at the 10-3 level to avoid experimental bounds from lepton avor changing processes. This dissertation shows that an enlarged R-parity can alleviate the lepton avor problem. An analysis of all sensitive parameters was performed in the mass range below 1 TeV, and we find that slepton maximal mixing is possible without violating bounds from the lepton avor changing processes: μ [arrow right] eγ; μ [arrow right] e conversion, and μ [arrow right] 3e. Topic three is the collider phenomenology of quirky dark matter. In this model, quirks are particles that are gauged under the electroweak group, as well as a \dark" color SU (2) group. The hadronization scale of this color group is well below the quirk masses. As a result, the dark color strings never break. Quirk and anti-quirk pairs can be produced at the LHC. Once produced, they immediately form a bound state of high angular momentum. The quirk pair rapidly shed angular momentum by emitting soft radiation before they annihilate into observable signals. This dissertation presents the decay branching ratios of quirkonia where quirks obtain their masses through electroweak symmetry breaking. This dissertation includes previously published and unpublished co-authored material.
Committee in charge: Dr. Davison Soper: Chair; Dr. Graham Kribs: Advisor; Dr. Ray Frey: Member; Dr. Michael Kellman: Outside Member

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Jenkins, Alejandro Wise Mark B. « Topics in particle physics and cosmology beyond the standard model / ». Diss., Pasadena, Calif. : Caltech, 2006. http://resolver.caltech.edu/CaltechETD:etd-06022006-145211.

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9

O'Leary, Benjamin Hugh. « Phenomenology of the minimal supersymmetric standard model without R-parity ». Thesis, University of Edinburgh, 2007. http://hdl.handle.net/1842/1982.

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This thesis is an investigation into the current bounds on the trilinear R–parity–violating couplings in the Minimal Supersymmetric Standard Model without R–parity conservation. The model is described, and its implications are discussed. Bounds on the couplings are obtained from leptonic and mesonic decay data, approximating mediating sfermions as much heavier than the decaying particles and assuming that only one set of couplings is non–zero for each decay. Those bounds from the purely leptonic decay data are compared to bounds from the LEP–II data, over a large range of sfermion masses. A potential signal of R–parity–violation at existing lepton colliders is calculated assuming that certain couplings are close to their bounds. The signal is found to be feasible and the backgrounds to the process are found to be negligible.

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Wade, Michael Fairbairn. « Semileptonic decays of heavy mesons and the standard model ». Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6045/.

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The formalism for a helicity amplitude analysis of the exclusive semileptonic decays of B mesons (B → Dlv and B → D* lv for l = e, µ and r) is introduced. In particular it is shown how measurements of the angular distribution of the subsequent decay D* → Dπ can fully determine the theoretically uncertain hadronic (B → D,D*) matrix elements. A spectator quark based model for the hadronic amplitudes is introduced, and then compared to other existing models and with the presently available experimental data, to extract the quark mixing matrix element |V(_eb)|. The extraction of |V(_ub)|, using exclusive models for b → u decays, is also discussed. The predictions of the free-quark model of inclusive semileptonic B decays are compared with those of the exclusive models, in an attempt to test the reliability of the inclusive model's predictions for |V(_eb)| and |V(_ub)|. A phenomenological analysis of experimental measurements of K(^0) – K(^0) and B(^0) – B(0) mixing is made, incorporating the above determinations of the mixing matrix elements, with a view to constraining the parameters of the standard model, such as the mass of the top-quark.

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Allison, Kyle F. « The standard model to the Planck scale ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:34c6b551-f525-4cf4-8032-c826b359bee4.

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The lack of direct evidence for physics beyond the SM at the LHC has led some to reevaluate the need for such physics to solve the hierarchy problem. Instead, the notion that the SM, or something like it, is valid up to the Planck scale and that technical naturalness is sufficient for solving the hierarchy problem has been suggested. This thesis examines minimal extensions of the SM that address its phenomenological and theoretical shortcomings while avoiding new physics between the electroweak and Planck scales that introduces a hierarchy problem. This thesis first studies two issues with the vMSM - an extension of the SM by three right-handed neutrinos - and their possible solutions. The first issue is the tension between dark matter production in the nuMSM and constraints from the Lyman-alpha forest data. To avoid this tension, the vMSM is extended by a Higgs singlet Φ and neutrino dark matter is produced through the decays of Φ rather than through left-right neutrino mixing. It is shown that the hierarchical parameters of this model can arise from symmetries broken at or near the Planck scale for two specific examples: one in which Φ stabilizes the electroweak vacuum and one in which Φ is a light inflaton. The second issue pertains to Higgs ξ-inflation. In the vMSM, a large non-minimal coupling ξ of the Higgs to gravity gives inflation but leads to a possible violation of perturbative unitarity below the inflationary scale. A study of Higgs ξ-inflation with M_h ≃ 125-126 GeV, for which the Higgs self-coupling λ runs to small values near the Planck scale, is carried out. It is shown that small λ can significantly reduce ξ required for inflation, but ξ cannot be small enough to address the possible unitarity issue. For small λ, a new region of Higgs ξ-inflation with a large tensor-to-scalar ratio r that is consistent with BICEP2 is discovered. This thesis then studies the technical naturalness and cosmology of a model that addresses the strong CP problem. It is shown that a classically scale invariant DFSZ invisible aξon model with a Peccei-Quinn scalar S, whose couplings to the SM are ultra-weak, can solve the strong CP problem and generate electroweak symmetry breaking via the Coleman-Weinberg mechanism. The ultra-weak couplings of S are natural due to an underlying approξmate shift symmetry. The model contains a light pseudo-Goldstone dilaton that can be consistent with cosmological bounds while the aξon can be the dark matter of the universe. Finally, a summary of the thesis is presented and future research topics are suggested.

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Heurtier, Lucien. « Particle physics and Cosmology beyond the Standard Model : Inflation, Dark Matter and Flavour ». Palaiseau, Ecole polytechnique, 2015. https://theses.hal.science/tel-01176578/document.

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Cette thèse se concentre sur l’étude des aspects de la physique au delà du modèle standard et de ses applications à la cosmologie. Depuis les temps reculés de l’évolution de l’Univers, jusqu’à la supersymétrie de basse énergie et à la phénoménologie des accélérateurs, des travaux variés ont été réalisés utilisant pour la majeure partie une formulation de basse énergie, et ce à des stades différents de l’Histoire de l’Univers. En effet, des modèles d’inflation sont présentés sous l’angle de théories effectives (à un champs) provenant de théories de hautes énergies issues de la supergravité et de la théorie des cordes. De plus, des modèles de matière noire incluant la présence d’une particule médiatrice sont étudiés à l’aide d’opérateurs effectifs de dimensions supérieures, générés explicitement à partir d’une théorie microscopique sous-jacente. De tels modèles semblent expliquer de récentes mesures du spectre de rayons X mesuré dans certains cluster de galaxies. Enfin l’étude des changements de saveurs dans l’extension supersymétrique incluant des jauginos de Dirac du modèle standard prédit des signatures expérimentales qui seront très probablement recherchées lors des prochaines acquisitions du LHC
This thesis has been focusing on beyond the Standard Model aspects of particle physics and their implication in cosmology. From the early times of the universe evolution, to current low energy supersymmetry and colliders phenomenology, various works have been achieved using mostly an effective, low energy formulation, at several different periods of the Universe History. Namely, models of Inflation are presented as effective single field theories arising from supergravity, string inspired UV completion models. Furthermore, models of dark matter including a mediator particle are studied with the use of effective higher dimensional operators that are generated explicitly from microscopic underlying theories. Such models were able to produce interesting results for explaining recent measurements on the X-rays spectrum of galaxy clusters. Finally, the study of flavour changing processes in the Dirac gaugino supersymmetric extensions of the Standard Model was explored in details, predicting some challenging signatures that are to be searched for at the next run of the LHC

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Bizi, Nadir. « Semi-riemannian noncommutative geometry, gauge theory, and the standard model of particle physics ». Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS413/document.

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Dans cette thèse, nous nous intéressons à la géométrie non-commutative - aux triplets spectraux en particulier - comme moyen d'unifier gravitation et modèle standard de la physique des particules. Des triplets spectraux permettant une telle unification on déjà été construits dans le cas des variétés riemanniennes. Il s'agit donc ici de généraliser au cas des variétés semi-riemanniennes, et d'appliquer ensuite au cas lorentzien, qui est d'une importance particulière en physique. C'est ce que nous faisons dans la première partie de la thèse, ou le passage du cas riemannien au cas semi-riemannien nous oblige à nous intéresser à des espaces vectoriels de signatures indéfinies (et non définies positives), dits espaces de Krein. Ceci est une conséquence de notre étude des algèbres de Clifford indéfinies et des structures Spin sur variétés semi-riemanniennes. Nous généralisons ensuite les triplets spectraux en triplets dits indéfinis en conséquence de cela. Dans la deuxième partie de la thèse, nous appliquons le formalisme des formes différentielles non-commutatives à nos triplets indéfinis pour formuler des théories de jauge non-commutatives sur espace-temps lorentzien. Nous montrons ensuite comment obtenir le modèle standard
The subject of this thesis is noncommutative geometry - more specifically spectral triples - and how it can be used to unify General Relativity with the Standard Model of particle physics. This unification has already been achieved with spectral triples for Riemannian manifolds. The main concern of this thesis is to generalize this construction to semi-Riemannian manifolds generally, and Lorentzian manifolds in particular. The first half of this thesis will thus be dedicated to the transition from Riemannian to semi-Riemannian manifolds. This entails a study of Clifford algebras for indefinite vector spaces and Spin structures on semi-Riemannian manifolds. An important consequence of this is the introduction of complex vector spaces of indefinite signature. These are the so-called Krein spaces, which will enable us to generalize spectral triples to indefinite spectral triples. In the second half of this thesis, we will apply the formalism of noncommutative differential forms to indefinite spectral triples to construct noncommutative gauge theories on Lorentzian spacetimes. We will then demonstrate how to recover the Standard Model

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Meisler, Terje R. « Lepton flavour violation in minimal supersymmetric extensions to the Standard model ». Doctoral thesis, Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-62.

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Buchanan, James Christopher. « A measurement of the ratio of the W+1 jet and Z+1 jet cross sections using the ATLAS detector at the LHC ». Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:16c481c8-b305-4890-a0d7-4dafd39deeec.

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The first measurement of the ratio of the W and Z cross sections in association with a single jet, known as the R_{Jets} measurement, is presented. The measurement was performed using 33pb^-1 of integrated luminosity, recorded during the year 2010 by the ATLAS detector at the LHC. At this time the LHC was operating at a center-of-mass energy of 7 TeV. The measurement is made as a function of the threshold on the jet transverse momentum, from 30 GeV up to a value of 200 GeV. The motivation for this measurement is outlined in terms of providing a stringent test of the Standard Model of particle physics, as well as a model independent tool for searching for new physics. Data driven tools are developed to perform the measurement and their performance is discussed. The result of the measurement is compared with the predictions of Next-to-Leading order perturbative QCD and found to be in good agreement over the entire range of transverse momenta considered.

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Rosa, Joao P. T. G. « Aspects of beyond the Standard Model string phenomenology ». Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:5e21fba9-9211-4adb-9c73-d27e98910f30.

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String theory is currently the best-known candidate for a theory of quantum gravity, having the necessary ingredients to describe all known elementary particles and interactions. It also includes several novel features, arising, for instance, from the additional six compact dimensions required for its internal consistency, making it the natural arena to construct extensions of the Standard Model. In this thesis, we analyze some of the new phenomenological aspects introduced by string theory within the framework of low energy effective theories, focusing on their applications to cosmology, astrophysics and collider experiments. We first consider a particular realization of the brane-world scenario in branonium bound states, showing that the orbital motion of a probe antibrane about a central brane stack leads to a resonant amplification of its world-volume scalar modes. We analyze the cosmological development of this process and also its potential relevance for either dark or baryonic matter generation in the early universe. We then focus on the spectrum of quark and lepton string excitations in warped compactifications, modeled by an effective 5-dimensional Randall- Sundrum throat. Motivated by the observed fermion mass hierarchy, we show that the spin-3/2 Regge excitation of the right-handed top quark is the lightest of such resonances in a significant region of parameter space, possibly lying below the TeV scale, and discuss its potential signatures at the Tevatron and at the LHC. Finally, we study the emission of sub-eV scalar particles by maximally rotating Kerr black holes, motivated by the recent string axiverse proposal. We focus on the spectrum of unstable scalar bound states in the superradiant regime, leading to an exponentially large axion cloud around astrophysical black holes, and analyze two semi-analytical methods for computing the growth rate of this instability, comparing the obtained results with previous analytical and numerical analyses.

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Maia, Marcilon Chaves. « An approach of the standard model of particle physics accesible to high school students ». Universidade Federal do CearÃ, 2011. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=6715.

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nÃo hÃ
Este trabalho tem como nÃcleo ou ponto central principal a exploraÃÃo de uma estÃria: âQuantolÃndia, a repÃblica das partÃculasâ, uma ficÃÃo criada pelo autor, na qual sÃo apresentados aspectos histÃricos, conceitos e idÃias da FÃsica das partÃculas elementares cujo propÃsito Ã oferecer uma maneira divertida e rica em analogias para apresentar o chamado âModelo padrÃo da fÃsica de partÃculasâ a estudantes do ensino mÃdio. A partir da estÃria busca-se construir o aprendizado apresentando as raÃzes da teoria atÃmica, as descobertas e conceitos que culminaram na atual modelagem das partÃculas elementares, bem como fazer consideraÃÃes sobre o status da teoria na atual conjuntura da FÃsica. Guiados por esse nÃcleo temÃtico, foram elaborados dois questionÃrios que foram aplicados em duas turmas de ensino mÃdio da cidade de Fortaleza em dois momentos diferentes: um antes e o outro apÃs ser apresentada a proposta da estÃria. Nestes questionÃrios testou-se nos alunos o nÃvel de conhecimentos com relaÃÃo aos pontos mais bÃsicos ou essenciais dos conteÃdos envolvidos no assunto. O chamado Modelo PadrÃo da FÃsica de PartÃculas, jÃ se sabia, pela experiÃncia do autor como professor (e isto foi comprovado pela aplicaÃÃo dos questionÃrios citados), nÃo ser um tema com o qual a maioria dos estudantes de ensino mÃdio estejam familiarizados. Alguns alunos mais bem informados atÃ jÃ âouviram falarâ alguma coisa sobre quarks, spin, quantum de energia, partÃculas virtuais ou outros termos tÃpicos do jargÃo da FÃsica, mas a grande maioria sequer tem uma noÃÃo adequada daquilo que conhecemos como âpartÃcula elementarâ. Dentro de uma das condiÃÃes da proposta de Ausubel de que o conteÃdo escolar a ser aprendido tem de ser potencialmente significativo, o significa ter de ser lÃgica e psicologicamente significativo, pensamos em uma forma simples, sem apelos a muitos recursos externos e quase sem nenhuma fÃrmula matemÃtica, de tentar viabilizar esse objetivo atravÃs da estÃria citada, cuja a intenÃÃo Ã cativar o aluno com apelo Ã curiosidade construtiva.
This work has, as a main purpose or focal point, to explore a story: "Quantumland, the Republic of particles," a fiction created by the author, which also presents historical aspects, concepts and ideas of elementary particles physics aiming to offer a funny way to introduce the so-called Standard Model of particle physics to high school students. From the story presentation we try to show some essential features of the atomic theory, with the discoveries and concepts that led to our nowadays knowledge about elementary particles, and also to show some considerations about the status of the theory in modern physics. Guided by this core theme we developed two questionnaires that were applied to two high school classes in Fortaleza and in two different moments: one before and one after the story introduction. These questionnaires tried to test the students background concerning the most basic or essential contents involved in the theme. The work showed that the so-called Standard Model of Particle Physics, as the author had already experienced in his job as a physics teacher (and proved by means of questionnaires mentioned) is not a familiar theme for most high school students. Some students (the most well-informed) have at most "heard" something about quarks, spin, quantum energy, virtual particles or other terms of the typical jargon of physics, but most of them do not even have an adequate grasp of what was known as a elementary particle. As one of the conditions of Ausubel's Meaningful Reception theory that learning must be potentially significant or has to be logical and psychologically meaningful, we thought of a simple way, without appeals to mathematical formulae that could facilitate the student learning of the ideas and guide him to a constructive curiosity.

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Kao, Yee. « Constraints on New Physics from Neutrino and Other Particle Experiments ». Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/40435.

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In this thesis we analyze a number of past, current, and future experiments to extract information on physics beyond the Standard Model. We use the Jacobi method to derive a set of simplified expressions for the probabilities of neutrino oscillations in matter. we show the possible constraints that can be placed on various models beyond the Standard Model. In several cases, we find that the limits thus thus obtained could be competitive with those expected from direct searches at the Large Hadron Collider. We then consider the possible effects of new physics beyond the Standard Model on precision measurements. In particular, we look at recent Bell/Babar results on the B meson branching fraction, and the bounds on Tau-decays from Babar. As a general framework of analyzing new physics beyond the Standard Model, we discuss what constraints can be placed on R-parity violating SUSY from these experiments. To complete our analysis, we update the single-coupling bounds on R-parity violating supersymmetry using the most up to date data as of October 2009. In addition to the data listed in the latest Review of Particle Properties, we utilize a new measurement of the weak charge of cesium-133, and preliminary Tau-decay branching fractions from Babar. Analysis of semileptonic D-decay is improved by the inclusion of experimentally measured form-factors into the calculation of the Standard Model predictions.
Ph. D.

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Wilson, Jonathan S. « A Search for the Standard Model Higgs Boson Produced in Association with Top Quarks ». The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1324333673.

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Vantalon, Thibaud. « Probing beyond the Standard Model physics using effective field theory ». Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/565736.

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Ara que el LHC ha proporcionat 120 fb-1 de dades, l'evidència d'una diferència d'energia entre el model estàndard (SM) i la nova física ha augmentat. Això fa que la teoria de camps efectiva (EFT) sigui un mètode versàtil per restringir la nova física amb una dependència mínima del model. En aquesta tesi, basada en el meu treball realitzat durant la meva candidatura a doctorat [1-4], fem ús de la tècnica EFT en diversos estudis. Comencem per estudiar l'extracció de acoblament trilineal del Higgs en els col·lisionadors actuals i futurs de leptons, utilitzant correccions de següent ordre en la producció de Higgs i producció de Higgs doble. Els nostres anàlisis minimitzen la dependència del model gràcies a l'ús de l'EFT. Argumentem que per restringir les diferents possibles desviacions al Model Estàndard, un ajust global amb la inclusió de tants observables com sigui possible és necessari. Hem trobat que la inclusió del trilineal en els processos únics d'Higgs tindrà un efecte marginal a LHC aconseguint una precisió d'ordre ú. La situació és diferent els futurs col·lisionadors de leptons, on l'alta precisió i la diferent energia de centre de masses poden donar el 50% de precisió. A continuació, ampliem l'EFT afegint un singlet escalar per estudiar les propietats del CP de la partícula que podria haver estat amagada després de l'infame excés de di-fotons a 750 GeV. Definim les asimetries sensibles al CP, tant en els canals de fusió de vectors com gluons, i estudiem el seu poder de diferenciar entre el CP imparell o fins i tot les hipòtesis. Finalment, ens movem de l'EFT i considerem un model simplificat de Higgs compost per comparar les mesures a baixa energia procedents de la mesura del dipol elèctric (EDM) de neutrons i electrons, amb les cerques al LHC. La teoria de camps efectiva no està completament absent, ja que calculem les correccions de dos loops al EDM de quarks i leptons lleugers que coincideixen amb el nostre model simplificat per als operadors de dimensions superiors i obtenim límits per al nostre model. A continuació, adaptem les cerques de l'LHC i comparem els límits actuals i futurs Hem trobat que el límit actual és competitiu amb el que proveeix la cerca directa de LHC, que és d'uns quants TeV. La futura actualització de l'experiment que permetrà mesurar el moment dipolar d'electrons ha de portar els límits al rang de 5-10 TeV.
Now the LHC has provided 120 fb−1 of data, the evidence for an energy gap between the Standard Model (SM) and new physics has grown strong. This makes effective field the- ory (EFT) a versatile method to constrain new physics with minimal model dependence. In this thesis, based on work done during my PhD candidature [1–4], we make use of EFT techniques in a variety of studies. We start by exploring the prospect of extracting the Higgs trilinear self-coupling at current hadron and future lepton colliders, using both higher order corrections to the single-Higgs process and di-Higgs production. Our anal- ysis minimizes model dependence thanks to the use of EFT. We argue that in order to constrain the different possible deviations to the Standard Model, a global fit with the inclusion of as many observables as possible is needed. We found that the inclusion of the trilinear correction in single-Higgs processes has a marginal effect at the LHC and will give a bound on the trilinear of order one. The situation is different at lepton col- liders, where the high precision and different running energies can give bound of order 50%. We then extend our EFT by adding a scalar singlet to study the CP properties of the particle which could have been behind the infamous 750 GeV di-photon excess. We define the CP sensitive asymmetries, in both the vector and gluon fusion channels, and study their power to differentiate between the CP odd or even hypotheses. Finally, we move somewhat away from EFT, and use a simplified model to compare the constraints on composite Higgs models coming from low energy neutron and electron electric dipole moment (EDM) measurements and LHC searches. Effective field theory is not completely absent, since we compute the two loop corrections of the light quarks and leptons EDM to match our simplified model to the higher dimensional operators of a low energy effective Lagrangian, and obtain bounds for our model. We then recast LHC searches and compare the present and future bounds. We found that the current bounds are competitive with the one coming from the LHC direct search and are of order a few TeV. The future upgrade of the experiment measuring the electron dipole moment should bring the bounds to the 5-10 TeV range.

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Hansen, Christian. « Neutrino Oscillations and Charged Higgs Bosons – Experimental Projects for Physics beyond the Standard Model ». Doctoral thesis, Uppsala University, Department of Nuclear and Particle Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5778.

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This thesis is based on work done in two different experimental projects.

The first project, the Tau RICH, is a previously proposed τ-neutrino appearance experiment for the CERN neutrino beam at the Gran Sasso laboratory in Italy. The proposed experimental concept is based on the use of focusing RICH detectors with liquid radiator (C₆F₁₄). Simulations made with a Geant4 code show that in the proposed experimental set-up, Cherenkov light from delta electrons will constitute a severe background that in practice would render the experiment unfeasible.

The second project, ATLAS, is a general purpose detector at the CERN 14 TeV proton-proton collider LHC which will start operation in 2007. To make the reconstruction and selection of the events in ATLAS more accurate, complete and up-to-date information on the interaction of the produced particles with the detector is needed. A service program code, the Material Integration Service (MIS), has been developed which makes use of the detector descriptions already available in a Geant4 code and which uses a novel algorithm, based on line integrals evaluated within small volume elements that build up the detector. This code is demonstrated to constitute a practically useful tool of satisfactory performance and accuracy.

The charged Higgs boson production in the gluon-bottom quark mode, gb → tH^±, followed by charged Higgs decays into a chargino and a neutralino, is studied for a specific choice of values for the Minimal Supersymmetric Standard Model (MSSM) parameters. It is shown, using a Monte Carlo code to simulate the ATLAS detector and the assumed MSSM physics model, that for an integrated luminosity of 300 fb^-1, in the intermediate region 4 < tanβ < 10 where H^± decays to SM particles cannot be used for H^± discovery, charged Higgs decays to non-SM particles can be used for Higgs discovery at the 5 σ significance level.

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Boddy, Christopher. « A search for the Standard Model Higgs boson via its decay to tau leptons and W bosons at the ATLAS detector ». Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:abba39e7-4de1-46c5-a533-7b677ae254f2.

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Understanding the origin or Electroweak symmetry breaking within the Standard Model was a key motivation for the construction of the Large Hadron Collider (LHC) experiment at CERN. This thesis presents a search for evidence of Higgs boson production in the 4.7 fb−1 of collision data recorded at a centre-of-mass energy of 7 TeV at the ATLAS detector during 2011. This search is focused on signal events in which a Higgs boson is produced in the mass range 100 < mH < 180 GeV/c2 and subsequently decays to a pair of W bosons or a pair of tau leptons to final states with one hadronically decaying tau lepton and one light lepton. After an event selection criteria has been applied, the number of events in this data sample is consistent with the total background estimate and an upper limit is placed on the SM Higgs boson production rate at 95% confidence level. In addition, the prospects for measuring the SM Higgs coupling strength to tau leptons with the associated Higgs production channels and the full LHC dataset are also presented.

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RADEMACHER, RICARDO JAVIER. « MINIMAL SUPERSYMMETRIC STANDARD MODEL PARAMETER SPACE EXCLUSION BY ANALYZING METASTABLE SCALAR VACUUM CONFIGURATIONS ». University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1022856740.

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Arnan, Vendrell Pere. « Building a Scenario of Physics Beyond the Standard Model in the Flavor Sector ». Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/670861.

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Recently lepton flavor universality tests in colliders have reported tensions with the Standard Model, providing an experimental hint at low energies of the effect of a new high energy theory. These tensions are known as flavor anomalies and that is why in this thesis we focus on the study of the impact of the flavor anomalies on the flavor sector of the Standard Model of particle physics. We introduce the Standard Model of particle physics and list the relevant tensions of the theory with the experiments in B decays, commenting in a brief manner the possible solutions involving new physics, as well as the main advantages and inconveniences of each new physics scenario. We first focus in a model with new heavy scalars and fermions were we only account for left-handed couplings to the Standard Model particles. We consider two possible models: one with an additional scalar and two vector-like fermions and another with two additional scalars and one vector-like fermion. The purpose of this model is to solve the tensions in FCNC decays, together with the anomalous magnetic moment of the muon, which are induced at loop-level in both models. We list the relevant constraints and show that the models are able to solve the anomalies, albeit a relatively large coupling of the muons is required. In the case of semi-leptonic decays, stringent constraints arising from B oscillations can be relaxed if the new fermions are considered Majorana particles. Then, since we cannot explain the muon magnetic moment with only left-handed couplings, we construct a model with new scalars and fermions allowing also for right- handed couplings, were we list the relevant Wilson coefficients for b quark decays to a strange quark and two muons, as well as the relevant observables acting as constraints for any number of new scalars and fermions. In order to illustrate this generic approach we supplement the Standard Model with a fourth generation of quarks and leptons. With this model we can explain FCNC anomalies and the magnetic moment of the muon avoiding all the constraints. The second kind of model that we explore is an extension of the Standard Model with scalar leptoquarks. In this case, we compute the Z- and W-decays to leptons for each one of the scalar leptoquarks at next-to-leading-logarithm approximation, and show that the finite terms can account for 20% of the total contribution for leptoquark masses of below 1.5 TeV. We also show their phenomenological relevance in a model with a singlet and a triplet, where our computation pushes the fit towards a better explanation of data. Besides, we comment on the fact that the B mixing has to be implemented carefully as it is one of the main constraints that was missing in earlier studies of these kind of models, and we also illustrate its key role in a particular model model, since it spoils the pure left- handed scenario with 2018 data. Finally, we scrutinize the FCNC process of b quark dcaying into an s quark and two leptons, in the framework of a two Higgs doublet model. We compute all the relevant Wilson coefficients performing the matching of the full theory with the low energy theory showing that it is necessary to keep the external momenta for the scalar and pseudo-scalar operators. This is the first time computation of a proper matching including all the relevant operators. We perform a phenomenological analysis of the model with the strange B meson decaying to two muons and the B meson decaying into two muons and a K meson at high momenta, where we have control of the hadronic uncertainties.
Des del 2012, una serie de mesures en experiments com BaBar, Belle i LHCb, han presentat tensions respecte el model estàndard en decaïments de mesons B. Aquestes desviacions són conegudes com les anomalies de sabor. En aquesta tesi interpretem les anomalies de sabor com a possibles efectes de nova física i proposem alguns models simples per poder acomodar les dades experimentals que difereixen del model estàndard. En primer lloc, proposem un model amb nous escalars i fermions pesats que només s’acoblen als fermions tipus esquerra del model estàndard. En aquest escenari intentem explicar una part de les anomalies ensems amb el valor anòmal del moment magnètic del muó. El resultat són uns acoblaments relativament grans de valor 2 aproximadament. Pel que fa a resoldre part de les anomalies, tenim la possibilitat de considerar els nous fermions com fermions de Majorana, que permet reduir el valor dels acoblaments. Per tal de poder relaxar el valor dels acoblaments d’una forma més general, en el següent capítol proposem un model semblant però amb acoblaments tipus dreta amb el model estàndard. En aquest model calculem totes les fórmules d’una manera genèrica i posteriorment ho particularitzem en un model de quarta generació. Amb la introducció d’aquests acoblaments tipus dreta combinats amb els esquerra podem explicar part de les anomalies de sabor i també el moment magnètic del muó. Seguidament, construïm un model amb leptoquarks escalars on estudiem alguns dels lligams més importants, com els decaïments de Z o les oscil·lacions del mesó B. Posteriorment, proposem models fenomenològics de 2 leptoquarks escalars on veiem l’impacte dels lligams estudiats anteriorment. També discutim com els models quedarien obsolets si no fos perquè les dades experimentals van canviar subtilment després de Moriond 2019. Per últim, fem un estudi de l’impacte de dos decaïments: del mesó B estrany a dos muons i del mesó B al mesó K i dos muons dins d’un model de dos doblets de Higgs. Aquí no ens centrem en les anomalies, sinó que mirem l’impacte d’aquests observables en el model i realitzem una comparació adequada entre la teoria efectiva i la teoria a altes enegies.

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Bard, Deborah. « Search for the inclusive b->d gamma decay at BaBar ». Thesis, University of Edinburgh, 2007. http://hdl.handle.net/1842/1556.

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Radiative penguin decays of B mesons are favour-changing neutral current (FCNC) processes, studies of which provide fertile ground for precision tests of the Standard Model. Because such decays must proceed through 1-loop or higher order processes, they are rare and their amplitudes are particularly sensitive to interference from other FCNC interactions beyond the SM. This thesis presents the search for the rare radiative penguin process b -> d gamma, carried out at the BABAR experiment.

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Bonnefoy, Quentin. « Topics beyond the Standard Model : axions, supersymmetry, string theory ». Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX034/document.

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Cette thèse a pour but l'étude de théories diverses, toutefois interconnectées, décrivant la nouvelle physique au-delà du modèle standard de la physique des particules. Ces sont des théories d'un nouveau type de particules, les axions, d'un nouveau principe de symétrie, la supersymétrie, et d'une nouvelle description des degrés de liberté fondamentaux, la théorie des cordes. Les progrès instrumentaux et théoriques constamment fait au fil des ans ont confirmé que ces théories sont des candidates privilégiées pour une description de la physique au-delà du modèle standard.Les axions sont d'abord examinés et étudiés d'un point de vue phénoménologique: nous présentons des modèles qui désenchevêtrent les différentes échelles qui décrivent l'espace des paramètres des modèles d'axions, et nous discutons les axions présents dans des modèles de saveur. Inspirés par les recherches autour du swampland, nous nous imposons l'utilisation de symétries de jauge, et non globales, en tant que point de départ pour la construction de modèles.Notre intérêt se porte ensuite sur la supersymétrie. Nous étudions sa brisure, à la fois dans des modèles explicites dans l'ultraviolet qui génèrent une échelle de brisure de supersymétrie basse à partir de matière à haute échelle, et au niveau des théories effectives à l'aide de la supersymétrie non-linéaire. En ce qui concerne ce dernier thème, nous nous restreignons à l'approche des superchamps contraints. Enfin, nous présentons des solutions classiques exactes d'un modèle supersymétrique dont la portée est grande, le modèle de Wess-Zumino d'un superchamp chiral.Finalement, nous nous intéressons à la théorie des cordes. Nous calculons des spectres de cordes en guise d'illustration de la structure de la théorie et de point de départ pour le calcul d'amplitudes du vide à une boucle. Celles-ci nous permettent de tester l'une des conjectures du swampland, qui désigne la gravité comme la plus faible des forces, dans une configuration de théorie des cordes où la supersymétrie est brisée. Enfin, les axions en théorie des cordes sont analysés, en particulier lorsqu'ils sont chargés sous une symétrie de jauge abélienne anormale
The aim of this thesis is to study various but interconnected theories for new physics beyond the standard model of particle physics. Those are theories of a new kind of particles, axions, a new symmetry principle, supersymmetry, and a new description of fundamental degrees of freedom, string theory. Constant instrumental and theoretical progresses made over the years maintain those already old subjects as leading BSM candidates.Axions are first reviewed and studied from a phenomenological perspective: we present models which disentangle the different scales which define the axion parameter space, and we discuss axions which arise in models of flavour physics. Motivated by swampland considerations, we insist on using gauge, and not global, symmetries as model building inputs.The focus then shifts to supersymmetry. We study its breaking, both in explicit ultraviolet models which generate a low supersymmetry breaking scale from high-scale matter, and at the effective field theory level using non-linearly realized supersymmetry. In our study of the latter topic, we focus on the constrained superfield approach. Finally, we present exact classical solutions of a supersymmetric model with broad application scope, the Wess-Zumino model of a chiral superfield.Last, we discuss string theory. We compute string spectra as illustrations of the structure of the theory and as starting points to compute one-loop vacuum amplitudes. Those are used to understand supersymmetry breaking in string theory, as well as brane interactions. Then, the latter enable us to test one of the swampland criteria, the weak gravity conjecture, in a string theory setup with broken supersymmetry. Finally, axions in string theory are scrutinized, in particular when they are charged under an anomalous abelian factor of the gauge group

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Dießner, Philip. « Phenomenological Study of the Minimal R-Symmetric Supersymmetric Standard Model ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-212431.

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The Standard Model (SM) of particle physics gives a comprehensive description of numerous phenomena concerning the fundamental components of nature. Still, open questions and a clouded understanding of the underlying structure remain. Supersymmetry is a well motivated extension that may account for the observed density of dark matter in the universe and solve the hierarchy problem of the SM. The minimal supersymmetric extension of the SM (MSSM) provides solutions to these challenges. Furthermore, it predicts new particles in reach of current experiments. However, the model has its own theoretical challenges and is under fire from measurements provided by the Large Hadron Collider (LHC). Nevertheless, the concept of supersymmetry has an elegance which not only shines in the MSSM. Hence, it is also of interest to examine non-minimal supersymmetric models. They have benefits similar to the MSSM and may solve its shortcomings. R-symmetry is the only global symmetry allowed that does not commutate with supersymmetry and Lorentz symmetry. Thus, extending a supersymmetric model with R-symmetry is a theoretically well motivated endeavor to achieve the complete symmetry content of a field theory. Such a model provides a natural explanation for non-discovery in the early runs of the LHC and leads to further predictions distinct from those of the MSSM. The work described in this thesis contributes to the effort by studying the minimal R-symmetric supersymmetric extension of the SM (MRSSM). Important aspects of its physics and the dependence of observables on the parameter space of the MRSSM are investigated. The discovery of a scalar particle compatible with the Higgs boson of the SM at the LHC was announced in 2012. It is the first and crucial task of this thesis to understand the underlying mechanisms leading to the correct Higgs boson mass prediction in the MRSSM. Then, the relevant regions of parameter space are investigated and it is shown that they are also in agreement with other Higgs observables. Another observable that is measured with great accuracy and especially sensitive to corrections from additional supersymmetric states is the mass of the W boson. Contributing effects within the MRSSM are identified and their dependency on the model parameters is studied. The presence of a stable supersymmetric particle as candidate for dark matter is a prediction of the MRSSM. The interplay of the relevant processes generating the correct abundance of dark matter in the universe and explaining the non-discovery by direct searches is investigated. Moreover, results of Run 1 of the LHC are used to study the electroweak MRSSM sector. This leads to a classification of viable regions of parameter space consistent with dark matter and LHC constraints. In the last part of this thesis the different observables are analyzed in coherence. This allows to identify valid regions of parameter space and highlights promising predictions of the MRSSM for the coming runs of the LHC and other experiments
Das Standardmodell (SM) der Elementarteilchenphysik liefert eine prägnante Beschreibung der Phänomene, welche die grundlegenden Bestandteile der Natur betreffen. Es verbleiben aber weiterhin offene Fragen und eine fehlende Einsicht in die zugrunde liegenden Strukturen. Supersymmetrie ist eine wohl begründete Erweiterung, welche es ermöglicht die beobachtete dunkle Materiedichte im Universum zu erklären und das Hierarchieproblem des SM zu lösen. Die minimale supersymmetrische Erweiterung des SM (MSSM) besitzt diese Eigenschaften. Darüber hinaus sagt es neue Teilchen in Reichweite aktueller Experimente vorher. Die eigenen theoretischen Herausforderungen des Modells und Einschränkungen durch Messungen am Large Hadron Collider (LHC) schränken es jedoch stark ein. Dennoch birgt das Konzept der Supersymmetrie eine Eleganz, die eine ansprechende Grundlage für weitere Modelle bietet. Daher ist es auch von Interesse, nicht-minimale supersymmetrische Modelle zu untersuchen. Diese bieten mit dem MSSM vergleichbare Vorteile und können dessen Diskrepanzen auflösen. R-Symmetrie ist die einzig mögliche globale Symmetrie, die nicht mit Super- und Lorentzsymmetrie kommutieren. Ein auf diese Weise konstruiertes Modell enthält somit alle grundlegenden Symmetrien einer Feldtheorie. Durch die Inklusion von R-Symmetrie können die bisherige Nichtentdeckung am LHC erklärt und vom MSSM unterscheidbare Vorhersagen gemacht werden. In dieser Arbeit wird die Untersuchung des minimale R-symmetrische supersymmetrische Erweiterung des SM (MRSSM). Wichtige Aspekte der Phänomenologie und die Abhängigkeit der Observablen von den Parametern des MRSSM werden untersucht. Die Entdeckung eines skalaren Teilchens kompatibel mit dem Higgs-Boson des SM am LHC wurde im Jahre 2012 bekannt gegeben. Die Untersuchung der zugrunde liegenden Mechanismen, welche die Masse des Higgs Bosons im MRSSM korrekt verwirklichen, ist Hauptbestandteil des erste Teils dieser Arbeit. Dabei wird der Parameterraum des Modells untersucht und gezeigt, dass auch Übereinstimmung mit weiteren Observablen der Higgsphysik möglich ist. Ein weitere wichtige Messgröße, welche mit hoher Genauigkeit bestimmt und empfindlich auf Beiträge supersymmetrischer Teilchen ist, ist die Masse des W Bosons. Beiträge innerhalb des MRSSM werden identifiziert und ihre Abhängigkeit von Modellparametern untersucht. Die Existenz eines stabilen supersymmetrischen Teilchens als Kandidat für dunkle Materie ist eine Vorhersage des MRSSM. Es wird untersucht, wie die relevanten Prozesse zusammenspielen, um die korrekte Dichte an dunkler Materie im Universum zu erzeugen und die Nichtentdeckung bei direkte Suche zu erklären. Des weiteren werden die ersten Ergebnisse des LHC verwendet, um den elektroschwachen Sektor des MRSSM zu untersuchen. Im letzten Teil dieser Arbeit wird das Zusammenspiel verschiedener Observablen analysiert. Auf diese Weise können erlaubte Parameterregionen festgestellt und Vorhersagen für zukünftige Experimente gemacht werden

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Shen, Chun. « The standard model for relativistic heavy-ion collisions and electromagnetic tomography ». The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1405931790.

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Makouski, Mikhail. « A measurement of top quark pair and photon production cross section with CMS detector ». Diss., Kansas State University, 2015. http://hdl.handle.net/2097/19188.

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Doctor of Philosophy
Physics
Andrew G. Ivanov
In this thesis the measurement of production cross section of top-quark pairs in association with a photon in proton-proton collisions at a center of mass energy of 8 TeV is presented. The data was recorded at the CMS experiment at the LHC in 2012. This measurement aims to extend our knowledge of top quark properties and help to test consistency of the Standard Model (SM) of particle physics. Data-driven methods are used to estimate the photon identification efficiency and purity. The measured cross-section agrees with the standard model expectation.

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Pernie, Luca. « Measurement of the Z boson pair-production cross section in proton-proton collisions at 7 and 8 TeV, and ECAL timing studies for the phase-2 upgrade of the CMS experiment ». Doctoral thesis, Universite Libre de Bruxelles, 2015. https://dipot.ulb.ac.be/dspace/bitstream/2013/216690/3/tdmPernie.pdf.

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The Large Hadron Collider (LHC) marks a new era for particle physics. Thanks to the very high energy of the proton beams, and to the large amount of data collected in years 2010-12, the physicists at CERN can test the standard model (SM) consistency, can explore the scalar sector, and search for any hint of new physics. A measurement of the Z boson pair production cross section using proton-proton collisions at 7 and 8 TeV center-of-mass energy, recorded by the CMS (Compact Muon Solenoid) experiment is presented. Diboson production at the LHC is of particular interest: it validates rare SM processes never tested before with high accuracy, it probes the electroweak boson self-interactions, and it constitutes a background for many physics searches such as the searches for the Higgs boson or supersymmetry. The ZZ production cross section is measured via the decay channel ZZ to 2l2v. The data used for the analysis have been recorded in years 2011 and 2012 by CMS and correspond to an integrated luminosity of about 5.1 fb-1 at 7 TeV and 19.6 fb-1 at 8 TeV. The data are selected requiring the presence of two isolated leptons (electrons or muons) of the same flavor with high transverse momentum (pT). In addition, events containing jets or additional leptons are vetoed, and it is applied a selection based on the dilepton pT, on the dilepton invariant mass, and on the transverse momentum imbalance (Emiss). The main SM backgrounds for this analysis are the Z/gamma+jet (Drell-Yan) process, the fully leptonic tt and single-top decay, and the WW and WZ diboson processes. The Z/gamma + jet process has no neutrinos in the final state, thus it has no large Emiss, but its cross section at the Z-peak is four orders of magnitude larger than the ZZ production. For this reason, even if the fraction of Z/gamma + jet events reconstructed with significant instrumental Emiss is not large, a high Emiss cut must be applied in order to improve the signal purity. High Emiss in Z/gamma + jet events is due to misreconstruction of physical objects, and to the additional energy deposits arising from the other proton-proton interactions occurring in the same bunch crossing (pileup). These effects are not well described in simulation, for this reason a high statistic control sample has to be used in order to model these tails from data. The fully leptonic tt, the single-top decay, and the WW process have been estimated in a control sample obtained requiring exactly one electron and one muon in the final state. The WZ process instead, has been estimated directly from the simulation. All the background shapes and normalizations are then constrained to data from a fit to the shape of a discriminating variable (e.g. Emiss), allowing only the ZZ signal normalization to freely vary. The selected data were also analyzed to search for anomalous triple gauge couplings (aTGC) involving the ZZ final state, and subsequently combined with the ZZ to 2l2l' final state data, to increase the sensitivity. In the absence of signs of new physics we set limits on the relevant aTGC parameters. Between 2023 and 2025, to extend its discovery potential and/or characterize any new signal possibly discovered, the LHC will increase its instantaneous luminosity by a factor of 10 beyond its design value. The increasing in luminosity will produce an average of 140 pileup interactions, this will represent an issue for the trigger and the reconstruction, degrading the jet and photon energy resolution and all the physic objects isolation quantities. In order to maintain full sensitivity, from low to high energy scales under severe pileup and radiation conditions, the L1 trigger, the tracker, the ECAL endcap and the HCAL, and the forward muon system will be upgraded. Moreover it will be fundamental to tag and remove the extra activity from PU interactions in order to correct the relevant variables measurements. The last part of the thesis will test the utility of timing in pileup mitigation and object reconstruction. Timing could be exploited for the association of photons, electrons and jets to their collision vertices, for particle identification, or to reject energy deposits coming from secondary vertices. A time measurement, extract from simulation, will be used in several reconstruction algorithms, showing improvements in particle reconstruction.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

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Hierro, Rodriguez Ignacio Miguel. « Scalars beyond the Standard Model : Composite Higgs, dark matter and neutrino masses ». Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3426319.

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This thesis deals with Composite Higgs (CH) models, dark matter and neutrino masses. In CH models, the Higgs is a pseudo-Goldstone boson of a high-energy strong dynamics. We construct CP-even and CP-odd bosonic effective chiral Lagrangian for a generic symmetric coset G/H. Assuming that the only sources of custodial symmetry are the ones present in the SM, we study the projection of this Lagrangian into the low-energy SM chiral Lagrangian. This is applied in three particular scenarios: the original SU(5)/SO(5) Georgi-Kaplan model, the minimal custodialpreserving SO(5)/SO(4) model and the minimal SU(3)/(SU(2)×U(1)) model, which intrinsically breaks custodial symmetry. We furthermore consider an extension of the Standard Model involving two new scalar particles around the TeV scale: a singlet neutral scalar φ, to be eventually identified as the Dark Matter candidate, plus a doubly charged SU(2)L singlet scalar, S++, that can be the source for the nonvanishing neutrino masses and mixings. Assuming an unbroken Z_2 symmetry in the scalar sector, under which only the additional neutral scalar φ is odd, we write the most general (renormalizable) scalar potential. This model may be regarded as a possible extension of the conventional Higgs portal Dark Matter scenario which in addition accounts for neutrino masses and mixings. This framework cannot completely explain the observed positron excess. However a softening of the discrepancy observed in conventional Higgs portal framework can be obtained, especially when the scale of new physics responsible, for generating neutrino masses and lepton number violating processes, is around 2 TeV.
Questa tesi si occupa di studiare modelli di Higgs Composto (HC), materia oscura e masse dei neutrini. In modelli di tipo HC, lo scalare di Higgs è uno pseudo-bosone di Goldstone associato che origina dalla rottura di una simmetria forte ad alta energia. Nella tesi costruiamo la Lagrangiana chirale bosonica effettiva, per un generico coset simmetrico G/H, derivando esplicitamente tutti gli operatori (sia CP-even che CP-odd) che appaiono fino a quattro derivate. Supponendo che l’uniche fonte di rottura di simmetria custodial siano quelle già presente nel Modello Standard (MS), studiamo la proiezione di questa Lagrangiana sulla Lagrangiana chirale di bassa energia del MS. Particolareggiamo questo studio considerando tre scenari particolari: il modello originale di Georgi-Kaplan SU(5)/SO(5), il modello minimale con simmetria custodial, SO(5)/SO(4), ed il modello minimale senza simmetria custodial, SU(3)/(SU(2) × U(1)). Nella tesi consideriamo inoltre unestensione del MS che coinvolge due nuove particelle scalari con massa alla scala TeV: un singoletto scalare neutro φ, che sarà poi identificato come candidato di materia oscura e un singoletto di SU(2)L scalare con carica q = 2, S++, che può essere la fonte per le masse e del mixing dei neutrini. Supponendo l’esistenza di una simmetria Z_2 nel settore scalare, sotto la quale solo φ è dispari, scriviamo il potenziale scalare (rinormalizzabile) più generale possibile. Il modello si può vedere come una possible estensione dei modelli con Higgs Portal in cui si tiene anche conto del meccanismo con cui generare le masse e i mixings dei neutrini. Il modello da noi studiato, pur predice un eccesso di positroni, non tale tuttavia da poter spiegare l’eccesso di positroni sperimentalmente osservato. Pur tuttavia si possono ottenere dei limiti meno stringenti rispetto ai normali modelli di Higgs Portal, in particolare se la scala della nuova fisica, responsabile della generazione delle masse dei neutrini e dei processi che violano il numero leptonico, è intorno ai 2 TeV.

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Sawyer, Craig Anthony. « Measurements of vector boson production in association with jets at the LHC using the ATLAS detector ». Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:9c8f606b-4b66-4a42-a200-11cf81ea84f0.

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This thesis presents measurements of the cross section for the production of a W boson in association with jets and the ratio of the cross sections for the production of a W boson and a Z boson in association with jets. Both measurements are performed in proton-proton collisions at √s = 7 TeV with the ATLAS experiment at the Large Hadron Collider using a dataset corresponding to an integrated luminosity of 4.6 fb^-1. The dataset allows for the exploration of a large kinematic range, including jet production up to a transverse momentum of 1 TeV and multiplicities up to seven jets. Results are presented as a function of jet transverse momenta and rapidities and as a function of event variables such as the scalar sum of the transverse momenta of the jets. Results as a function of dijet angular variables are also presented. The measurements are compared to several state-of-the-art QCD predictions including next-to-leading-order perturbative calculations, resummation calculations and Monte Carlo generators. Finally, the effect of the results on parton distribution functions is explored.

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Wouda, Glenn. « Phenomenology of Higgs Bosons Beyond the Standard Model ». Doctoral thesis, Uppsala universitet, Högenergifysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-240617.

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After a long history of searches, a Higgs boson H was discovered by the ATLAS and the CMS experiments at the Large Hadron Collider (LHC) in 2012. Its properties ﬁt well the ones predicted by the Standard Model (SM) of particle physics. However, the SM can not explain other established properties of Nature, such as the existence of Dark Matter. For this reason, models beyond the SM should be considered. Such models often predict the existence of several Higgs bosons and this thesis explores some of those models. In particular, the possibility to discover a charged Higgs boson, which would be a clear sign of physics beyond the SM, is studied. A commonly studied extension of the SM is the framework of two-Higgs-doublet models (2HDMs), where there are ﬁve Higgs bosons. By confronting the parameter spaces of some 2HDMs with publically available data from the LHC, the prospects for ﬁnding the 2HDM Higgs bosons is presented through the calculation of production cross sections and decay branching ratios in various channels. A new kind of 2HDM, called the Stealth Doublet Model is presented and the properties of the Higgs bosons are studied. In this model, it is shown that in particular the properties of the charged Higgs boson H± have new features not exhibited in earlier studied models. Within the parameter space compatible with the LHC results, the production cross section for H± can be sizeable enough to be experimentally observed. Finally, the discovery prospects at the LHC, for a H± in the pp → tH± process, with the decays H± → HW± and H → bb, is studied in various models beyond the Standard Model. It is shown that for the supersymmetric models, this channel is beyond the discovery reach of the LHC. In some of the other studied models, in particular the Aligned 2HDM, the situation is improved and the channel is feasible.

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Larner, Aimee Bridget. « Measurement of the Z—>TlTh cross-section and search for the standard model vector boson fusion produced Higgs —>TlTh at ATLAS ». Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:1b7174f0-802f-40ac-9ae9-bc0c589e4d6e.

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This thesis presents a cross-section measurement of the Z -+ TeTh process performed using the ATLAS detector at the Large Hadron Collider at CERN. The data used were collected at a centre-of-mass energy of 7 TeV during 2010 and corresponds to an integrated luminosity of 36 pb-I. This measurement uses the final state where one T lepton decays leptonically, to an electron or muon, plus neutrinos, and the other T lepton decays hadronically. The "(* / Z -+ a, It and di-boson background processes are estimated using Monte Carlo simulation, the W -+ TV Monte Carlo background prediction is estimated using a semi data-driven method. The multijet background is estimated with a fully data-driven 'ABCD' method using three exclusive control regions built by inverting uncorrelated requirements on the isolation of the electron or muon and the product of the electric charge of the identified electron or muon and hadronically decayed T lepton. The measured cross-sections in each channel are corrected for the individual branching ratios and yield the total cross-section a(Z -+ TT, minv 66 - 116 GeV) = 1142 ± 135.5(stat.) ± 206.2(syst.) ± 40. 19(1umi.) ± 3.6(theo.) pb for the electron channel and a(Z -+ TT, minv 66 - 116 GeV) = 857.6 ± 81.4(stat.) ± 132.5(syst.) ± 30.19(lumi.) ± 2.8(theo.) pb for the muon channel, where the invariant mass of the Z boson is between 66 and 116 GeV. These are in good agreement with the theoretical prediction of960 ± 49.5 pb. Performing a measurement of a well-known Standard Model process using the ATLAS de- tector in this new high energy regime is essential for validating the T lepton identification in particular, which is essential for any new physics search such as H -+ TeTh' A cut-based analysis for the Vector Boson Fusion produced Higgs boson decaying to two T leptons channel is introduced and the possibility of using the more complex analysis technique, the Matrix Element method, to increase sensitivity is discussed.

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Sciandra, Andrea [Verfasser]. « Probing the Standard Model of particle physics with ttH, WWZ and WZZ multilepton final states / Andrea Sciandra ». Bonn : Universitäts- und Landesbibliothek Bonn, 2020. http://d-nb.info/120447964X/34.

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Bianco, Gianluca. « Study of the quantum interference between singly and doubly resonant top-quark production in proton-proton collisions at the LHC with the ATLAS detector ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/22108/.

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The top quark is the heaviest known elementary particle of the Standard Model. Thanks to its particular properties, it allows to explore unique physics domains, inaccessible otherwise. One of them is the quantum interference between singly (tW) and doubly (t ̄t)resonant top quark production in proton-proton collisions, which can lead to identical WbWb final-states when an additional b-quark is radiated during a singly-resonant production. Studying this process is very important for a better knowledge of the Standard Model, but also to investigate some Beyond the Standard Model processes: for example,the search for top squarks suffers a large background contamination fromt W and t ̄t in the interference region. In this work, the measurement of the particle-level differential cross-section of the WbWb final-state in the eμ dilepton channel is provided, in order to better investigate the interference-sensitive region of these processes. The measurement is performed using the full dataset collected by the ATLAS detector from proton-proton collisions at the LHC during Run-2 at √s= 13 TeV corresponding to an integrated luminosity of 139 fb−1. The differential cross-section has been measured as a function of two interference-sensitive variables, defined as mminimaxbl and ∆R(b1,b2). Besides the single-differential cross-sections as a function of mminimaxbl and ∆R(b1,b2), also the double-differential cross-section as a function of mminimaxbl in bins of ∆R(b1,b2) is measured. The WbWb differential cross-section has been successfully extracted and compared to different schemes: the Diagram Removal and the Diagram Subtraction. This twopredictions model in a different way the quantum interference description.

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Andrean, Stefio Yosse. « Search for Stop Using the ATLAS Detector and Performance Analysis of the Tile Calorimeter with Muons from W Decays ». Licentiate thesis, Stockholms universitet, Fysikum, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-191555.

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This thesis presents a search for the supersymmetric partner of the top quark in the final state with one lepton. The search focuses especially in the region of the parameter space where the 2-body decay dominates. The analysis is performed using LHC full Run 2 data at √s = 13 TeV as recorded by the ATLAS detector. No significant excess above the backgrounds is observed, and 95% confidence level exclusion limits are calculated in the stop-neutralino mass plane. Stops are excluded up to 1200 GeV in the low neutralino mass scenario of below 400 GeV. The Tile Calorimeter is part of the ATLAS calorimeter system whose main task is to measure the energy of hadrons. A performance study is conducted on the Tile Calorimeter using muons from W boson decay originating from proton-proton collisions. Each calorimeter cell response is measure in data and compared with detector simulation. The azimuthal cell response uniformity is also investigated using a likelihood method. Overall, a good data to detector simulation agreement and azimuthal uniformity is observed which shows well-calibrated cells and uniform responses among the calorimeter modules.

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Reinsch, Andreas, et Andreas Reinsch. « Search for Colorful Quantum Black Holes Decaying to an Electron-Jet Final State with the ATLAS Experiment ». Thesis, University of Oregon, 2012. http://hdl.handle.net/1794/12370.

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A search for quantum black holes with color charge decaying to one electron and one quark has been performed using data collected by the ATLAS Experiment at the Large Hadron Collider corresponding to 2.29 fb−1. No excess over the expected Standard Model interactions has been observed. Limits are set on the production cross section for events with one electron and one jet resulting from new physical phenomena. Models with a combined invariant mass of the electron and jet larger than or equal to 2.5TeV and a cross section above 2.6 fb are excluded at the 95% confidence level. This allows the exclusion of a significant part of the parameter space of quantum black hole models.

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Tosi, Mia. « Feasibility of the SM Higgs boson search in the channel H ->ZZ^*->mumubb via VBF at sqrt(s)=7TeV with the CMS experiment ». Doctoral thesis, Università degli studi di Padova, 2011. http://hdl.handle.net/11577/3427394.

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One of the main goals of the now-running Large Hadron Collider (LHC) machine at CERN in Geneva is to elucidate the mechanism of electroweak symmetry breaking, and in particular to determine whether a Standard Model Higgs boson exists or not. For this aim, and in general to explore the high-energy frontier of particle physics, the LHC produces proton-proton collisions in the core of two multi-purpose experiments: ATLAS and CMS. In the Compact Muon Solenoid (CMS) experiment one of the most promising discovery modes of the Higgs boson is the one involving the decay into two Z bosons, with a subsequent decay of the Z pair in a fully leptonic final state. Among the various production mechanisms for the Higgs boson, vector-boson fusion (VBF) offers certainly one of the most distinctive and interesting signals. In this thesis I report an analysis of the feasibility of the search for Higgs decays in the $H\rightarrow ZZ\rightarrow l^+l^-jj$ decay channel with the CMS detector. Allowing for a $Z$ boson to decay to a jet pair entails a large increase of backgrounds in exchange for a tenfold increase in the total branching ratio. The analysis of the di-lepton plus di-jet final state may furthermore provide ground for interesting additional searches and measurements. An optimization of the search for the Higgs decay signal has been performed using the key observables of this Higgs VBF production mechanism, applying the multivariate technique called {\em boosted decision trees'} for data selection in two successive stages. The application of $b$-jet tagging is also used to try and favorably select $b$-enriched final states, strongly suppressing the main background due to $Z$ production associated to light quarks at the cost of a 4.5 reduction factor of selectable signal events. Results on the signal significance achievable with $30\ fb^{-1}$ of collisions with the optimized Higgs candidate selection are presented. The LHC provided proton-proton collisions at the centre-of-mass energy of $7\ TeV$ from March $30^{th}$ to November $8^{th}$ 2010. During the 2010 run CMS collected an integrated luminosity of $43.2\ pb^{-1}$. Despite being utterly insufficient for a meaningful Higgs boson search, these data have been used to test the analysis strategy and the signal selection methodology. Limits to the ratio between signal cross section and SM-predicted cross section as a function of the Higgs boson mass have been obtained with the available data.
Uno degli obiettivi principali del Large Hadron Collider (LHC) in funzione al laboratorio CERN di Ginevra \'e di svelare il meccanismo della rottura della simmetria elettrodebole, e in particolare di determinare se il bosone di Higgs del Modello Standard esista o meno. A questo scopo, e in generale per esplorare la frontiera di alta energia della fisica delle particelle, l'LHC produce collisioni protone-protone al centro di due esperimenti multi-funzione: ATLAS e CMS. All'esperimento CMS (Compact Muon Solenoid) uno dei modi pi\'u promettenti per scoprire il bosone di Higgs consisten nello studiare il decadimento in due bosoni Z, con un successivo decadimento della coppia di Z in uno stato finale puramente leptonico. Fra i vari meccanismi di produzione del bosone di Higgs, la fusione di bosoni vettori (VBF, da Vector-Boson Fusion) offre certamente uno dei segnali pi\'u interessanti e distintivi~\cite{Cahn:1983ip,Kane:1984bb,Kleiss:1986xp}. In questo lavoro viene descritta l'analisi della fattibilit\'a della ricerca di decadimenti del bosone diHiggs nel canale di decadimento $H\rightarrow ZZ\rightarrow l^+l^-jj$ con il rivelatore CMS. Permettendo a un bosone Z di decadere in una coppia di jets si subisce un grande aumento dei processi di fondo in cambio di un aumento di un fattore 10 nella frazione di decadimento totale. L'analisi dello stato finale con dileptoni e coppie di jets pu\'o inoltre creare le condizioni di interessanti ricerche e misure addizionali. Una ottimizzazione della ricerca del segnale di decadimento del bosone di Higgs \'e stata ottenuta usando le quantit\'a osservabili pi\'u significative del meccanismo di produzione di Higgs via VBF, applicando una tecnica multivariata chiamata {\em boosted decision trees} per la selezione dei dati in due fasi distinte. L'applicazione dell'identificazione di jets da $b$-quarks \'e anche usata per cercare di selezionare favorevolmente stati finali ricchi di $b$-quarks, riducendo fortemente il fondo principale dovuto alla produzione di bosoni $Z$ associati a jets da quarks leggeri o gluoni, al costo di una riduzione di un fattore 6 nel numero di eventi di segnale selezionabili. La tesi presenta i risultati per la significanza del segnale ottenibili con $30\ fb^{-1}$ di collisioni protone-protone a 7 TeV, usando la selezione ottimizzata dei candidati decadimenti del bosone di Higgs. Durante il 2010 LHC ha fornito collisioni protone-protone all'energia del centro di massa di 7 TeV dal 30 marzo al 8 novembre. In questo run CMS ha raccolto una luminosit\'a integrata pari a $43.2\ pb^{-1}$. Nonostante questi dati siano assolutamente insufficienti per una ricerca del bosone di Higgs, questi dati sono stati utilizzati per un test della strategia di analisi e della metodologia di selezione del segnale. Limiti al rapporto fra la sezione d'urto del segnale e la sezione d'urto prevista dal Modello Standard in funzione della massa del bosone di Higgs sono stati ottenuti con i dati a disposizione.

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Stål, Oscar. « Physics at the High-Energy Frontier : Phenomenological Studies of Charged Higgs Bosons and Cosmic Neutrino Detection ». Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-111162.

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The Standard Model of particle physics successfully describes present collider data. Nevertheless, theoretical and cosmological results call for its extension. A softly broken supersymmetric completion around the TeV scale solves several of the outstanding issues. Supersymmetry requires two Higgs doublets, leading to five physical Higgs states. These include a pair of charged Higgs bosons H±, which are a generic feature of theories with multiple Higgs doublets. Using results from high-energy colliders and flavour physics, constraints are derived on the charged Higgs boson mass and couplings; both for constrained scenarios in the minimal supersymmetric standard model (MSSM) with grand unification, and for general two-Higgs-doublet models. The MSSM results are compared to the projected reach for charged Higgs searches at the Large Hadron Collider (LHC). At the LHC, a light charged Higgs is accessible through top quark decay. Beyond a discovery, it is demonstrated how angular distributions sensitive to top quark spin correlations can be used to determine the structure of the H±tb coupling. The public code 2HDMC, which performs calculations in a general, CP-conserving, two-Higgs-doublet model, is introduced. In parallel to the developments at colliders, the most energetic particles ever recorded are the ultra-high-energy (UHE) cosmic rays. To gain more insight into their origin, new experiments are searching for UHE neutrinos. These searches require detectors of vast volume, which can be achieved by searching for coherent radio pulses arising from the Askaryan effect. The prospects of using a satellite orbiting the Moon to search for neutrino interactions are investigated, and a similar study for an Earth-based radio telescope is presented. In both cases, the method is found competitive for detection of the very highest energy neutrinos considered.

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Smith, Geoffrey N. « A Search For the Standard Model Higgs Boson Produced in Association with Top Quarks in the Lepton + Jets Channel at CMS ». The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397747965.

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Eygi, Zeynep Deniz. « The Standard Model Analyasis Of The Cp Violation In The Inclusive Semileptonic B-meson Decays ». Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12604712/index.pdf.

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Being a flavor changing neutral current process, inclusive semileptonic B- meson decays provide reliable testing grounds for the Standard Model at the loop level. They are also importanat in the CKM phenomology and investing the CP violation due to the existence of sizable interference terms in the decay amplitude. In this work , the rare inclusive semileptonic B- meson decays for (lepton is electron ,muon , tau) are investigated in the context of the Standard Model.The differential branching ratio, forward-backward asymmetry ,CP &ndash
violating asymmetry and CP &ndash
violating asymmetry in the forward-backward asymmetry in these processes are examined.The dependencies of these physical parameters on the Standard Model parametres are analyzed by paying a special attention to the long distance effects. Although the branching ratios predicted for the inclusive semileptonic B- meson decays are relatively small because of CKM suppression , it has been found that there is a significant ACP and ACP(AFB) for these processes.

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Coniavitis, Elias. « Charged Higgs Bosons at the ATLAS Experiment and Beyond ». Doctoral thesis, Uppsala universitet, Högenergifysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-111576.

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In the ATLAS experiment at the Large Hadron Collider (LHC) at CERN, direct searches for the elusive Higgs boson will be conducted, as well as for physics beyond the Standard Model. The charged Higgs boson (H±) is interesting both as a part of the Higgs sector, and as a clear sign of new physics. This thesis focuses on H± searches, with H± production in top-antitop pair events, and in particular the bW± bH±, H±→τhadν, W±→qq channel. Its potential was investigated as part of a larger study of the expected performance of the entire ATLAS experiment. Full simulation of the ATLAS detector and trigger was used, and all dominant systematics considered. It was shown to be the most promising H± discovery channel for mH±<mt. As hadronic τ decays are important for H± searches, their correct identification is critical. Possibilities of improving tau-jet identification in pile-up and top-antitop pair events were investigated. Redundant or even performance-reducing variables in the default likelihood identification were identified, as were new variables showing discriminatory power. This allows for increased rejection of QCD jets in these environments, and higher robustness of the method. Before any physics studies, a commissioned and well-understood detector is required. The Lorentz angle of the ATLAS Semi-Conductor Tracker (SCT) barrel was measured using 2008 cosmic-ray data. It is an important observable for the performance of several detector aspects. Potential sources of systematics were investigated and evaluated. The Lorentz angle in the SCT barrel was measured as θL = 3.93 ± 0.03(stat) ± 0.10(syst) degrees, agreeing with the model prediction. The Compact Linear Collider (CLIC) is a proposed successor to the LHC. The potential for charged and heavy neutral Higgs bosons at CLIC was investigated, in terms of both discovery and precision measurement of parameters like tanβ or the Higgs masses, up to and beyond 1 TeV, which would be challenging at the LHC

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Alpigiani, Cristiano. « Search for rare B decays into two muons with the ATLAS detector ». Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8922.

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The impressive progress that elementary particle physics made in the second half of the last century led to the formulation of a comprehensive theory, known as the Standard Model (SM), which correctly describes all fundamental interactions in nature, except for the gravitational one. Indirect discoveries have always played an important role in high energy physics scenario and indirect research can be considered to all intents and purposes complementary to the direct one, since allows to test much higher energy scales than those the current colliders are able to reach. This is very important now that electroweak precision tests and measurements on Flavour Changing Neutral Currents (FCNC) processes put very stringent constraints on physics beyond the SM, requiring it to appear at scales O(10 TeV). On the other hand, New Physics (NP) is expected already at scales O(1 TeV) in order to offer a natural explanation to the smallness of the Higgs mass. This scale is also confirmed by recent constraints on thermal dark matter [1] which show how new physics should manifest not far above the electroweak scale. Rare B decays have always played a crucial role in shaping the flavour structure of the SM and particle physics in general. Since the first measurement of rare radiative B æ Kú“ decays by the CLEO Collaboration [2] this area of particle physics has received much experimental and theoretical attention. In particular, FCNC B decays, involving the b-quark transition b æ (s, d) + “ and b æ (s, d) + ¸+¸≠(¸ = e, μ, ·, ‹), provided crucial tests for the SM at the quantum level since they proceed through loop or box diagrams, and they are highly suppressed in the SM (also by helicity). Hence, these rare B decays are characterised by their high sensitivity to NP. The B0 s æ μ+μ≠ channel is the most direct example of the b æ s ¸¸ transitions. The SM predicted branching ratio [3] can be enhanced by coupling to non-SM heavy particles, such as those predicted by the Minimal Supersymmetric Standard Model (MSSM) and other extensions. Updated measurements on the B0 s æ μ+μ≠ branching ratio have been presented by ATLAS [4], LHCb [5] and CMS [6] collaborations. In this thesis I will report all the studies I performed within the rare B decays ATLAS group, measuring the branching ratio of the B0 s æ μ+μ≠ channel on data collected during LHC Run 1. The first chapter provides a general introduction to the SM, focusing in particular on the flavour sector and the possible new physics scenarios. Chapter 2 briefly introduces the LHC collider and the ATLAS detector, detailing the muon and trigger systems, fundamental for the rare B decays measurements. In chapters 3 and 4, I will summarise the work done, during my presence at CERN, on the ATLAS semiconductor strip detector, monitoring the Lorentz angle during Run 1 and measuring the backplane resistance of the silicon modules installed in the ATLAS cavern. In chapter 5, I will review the strategy adopted to measure the B0 s æ μ+μ≠ branching ratio, reporting all the studies I performed on the combinatorial background, and the results obtained on 4.9 fb≠1 of data collected in 2011. Chapters 6 and 7 detail respectively the additional studies I performed on the 2011 datasets and all the tests I made in preparation for the analysis on 20 fb≠1 of data collected in 2012. I will show the studies on the discriminating variables for the rejection of the background, the tests on the multivariate analysis and on the possible strategies for the invariant mass fit for the extraction of the signal yield. All these studies proved to be fundamental for the 2012 measurement detailed in chapter 8.

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Netto, Dorival Gonçalves. « Sinais de produção de novos bósons vetoriais no LHC ». Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-26042010-141529/.

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Neste trabalho realizamos uma abordagem fenomenológica da observação de novos bósons de spin-1 associados ao setor de Quebra de Simetria Eletrofraca. Como motivação a essa análise estudamos primeiramente o caso especial de modelos baseados no mecanismo de Quebra espontânea de Simetria por Condições de Contorno, os quais também apresentam uma torre de bósons vetoriais de Kaluza-Klein assegurando a unitariedade no espalhamento entre bósons gauge. Na análise fenomenológica efetuamos uma abordagem independente de modelo analisando o potencial do Large Hadron Collider (LHC) na detecção de novos bósons vetoriais associados ao setor de quebra de simetria.
In this work we performed a phenomenological observation of new spin-1 bosons associated with the Electroweak Symmetry Breaking sector. As motivation for this analysis we previously studied the special case of models based on the mechanism of Eletroweak Symmetry Breaking via Boundary Conditions, which also have a tower vector of Kaluza-Klein bosons ensuring unitarity in scattering between gauge bosons. In the phenomenological analysis we performed a model independent approach to analyzing the potential of the Large Hadron Collider (LHC) in the detection of new vector bosons associated with the symmetry breaking sector.

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Kanik, Inanc. « Light Cone Qcd Sum Rules And Meson Physics ». Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/2/12610082/index.pdf.

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In this thesis, we applied Light Cone QCD sum rules (LCSR) to several problems in meson physics. Semileptonic B->
eta l v decays are important to get information on Cabibbo-Kobayashi-Maskawa (CKM) matrix elements. We calculated form factors of this decay in LCSR frame. Our results are confirmed by later studies and these similar studies had been used for enhancing result on b to u quark transition matrix element of CKM matrix by BaBar collaboration. We used LCSR method also for calculating coupling constant of radiative rho ->
eta photon decay since the analysis of the vector particle to pseudoscalar particle radiative decay with eta and eta'
mesons in final state can provide insights to the long standing issue of the eta and eta'
mixing. Our result g_{rho eta photon}=(1.4 ±
0.2) is very close to experimental value g_{ rho eta photon} = (1.42 ±
0.12). We also calculated magnetic moment of the rho meson in LCSR frame which is an important parameter since it is strongly related to internal structure of hadron. Our result 2.3 ±
0.5 in units of (e/2m_rho), is in better agreement with lattice QCD results than traditional QCD sum rules. Quark contents of light scalar mesons are still under debate and we analyzed phi ->
K K decays which is important for understanding the quark content of the f0 meson. Our final result is g_{phi KK} = 4.9 ±
0.8 which is in well agreement with existing experimental result g_{phi KK} = 4.8.

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47

Hansson, Per. « First Determination of the Electric Charge of the Top Quark and Studies of the Top Quark Pair Background to New Physics ». Doctoral thesis, Stockholm : Particle and astroparticle physics, Department of physics, Royal institute of technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4870.

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48

Zimmer, Stephan. « Charged Higgs Boson Studies in the Channel pp→a₁h^±→4b+l+MET in the Next-to MSSM (NMSSM) with the ATLAS Experiment ». Thesis, Uppsala University, High Energy Physics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-119324.

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Next-to-minimal super-symmetric extensions of the Standard Model (SM) predict the existence of several non-SM like Higgs bosons. The process pp→a₁h^±→4b+W involves the production and the decay of a spin-0 charged Higgs boson and a CP-odd Higgs boson a₁ which can have a sizable cross section in the NMSSM. The invariant masses of these intermediate bosons can be reconstructed from the four momenta of the final state particles using mass minimization algorithms. This thesis presents a cut-based analysis of two mass scenarios and specialized algorithms that are capable of recovering the signal in a large background arising from Standard Model processes such as ttbar. The analysis is tested with a realistic ATLAS detector simulation investigating trigger efficiencies and probing several jet reconstruction algorithms.

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49

Zimmer, Stephan. « Charged Higgs Boson Studies in the Channel pp→a1h±→4b+l+MET in the Next-to MSSM (NMSSM) with the ATLAS Experiment ». Thesis, Uppsala universitet, Högenergifysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-119324.

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Next-to-minimal super-symmetric extensions of the Standard Model (SM) predict the existence of several non-SM like Higgs bosons. The process pp→a1h±→4b+W involves the production and the decay of a spin-0 charged Higgs boson and a CP-odd Higgs boson a1 which can have a sizable cross section in the NMSSM. The invariant masses of these intermediate bosons can be reconstructed from the four momenta of the final state particles using mass minimization algorithms. This thesis presents a cut-based analysis of two mass scenarios and specialized algorithms that are capable of recovering the signal in a large background arising from Standard Model processes such as ttbar. The analysis is tested with a realistic ATLAS detector simulation investigating trigger efficiencies and probing several jet reconstruction algorithms.

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50

McBride, Sachiko Toda. « Measurement of the Zγγ production cross section at proton-proton collisions with the CMS experiment ». Diss., Kansas State University, 2016. http://hdl.handle.net/2097/32204.

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Doctor of Philosophy
Department of Physics
Yurii Y. Maravin
This thesis presents the first study of a rare production of Z boson in association with two photons (Zγγ), where the Z boson decays into a pair of muons or electrons, by proton-proton collisions at the Large Hadron Collider (LHC). This study uses full data samples that have been collected with the Compact Muon Solenoid (CMS) detector in 2012 with a center of mass energy of 8TeV, corresponding to an integrated luminosity of 19.7 fb⁻¹. The Zγγ production cross section is measured within a fiducial region defined by two leptons with two photons where transverse momentum over 15 GeV and distance between gamma and lepton above 0.4. Using the obtained samples, the Zγγ cross section is measured to be: 12.6 ±1.6 (stat.) ± 1.7 (syst.) ± 0.3 (lumi.) fb. where stat., syst., and lumi. denote the statistical uncertainty, systematic uncertainty, and the uncertainty in integrated luminosity, respectively. This result is in an excellent agreement with the theoretical prediction of 13.0 ± 1.5 fb.

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Thèses sur le sujet « Particle Physics - Standard Model (SM) »

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