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Dissertations / Theses on the topic 'Standard Electroweak Model'
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Fromme, Lars. "Electroweak baryogenesis in extensions of the standard model." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980804515.
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Díaz, Méndez Enrique. "Electroweak scale neutrinos." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Yamashita, Hiroki 1981. "Electroweak phase transition and singlet Majoron model." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101691.
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First, we review the basics of baryogenesis and models for baryogenesis in the early literature. Then, we discuss the main theme in this thesis, electroweak baryogenesis, which utilizes the electroweak phase transition. We present how the phase transition can be used to achieve baryogenesis. Next, we develop our model, which is the Standard Model with a singlet field coupled to the Higgs doublet negatively and to the right-handed neutrinos. It is a simple extension of the singlet Majoron model. We focus on numerical analysis of the model. Parameter space satisfying all the conditions are found and relevant quantities, such as the critical temperature, the Higgs mass, and the mixing angle are found as well. It turns out that LEP bound on the Higgs mass and the mixing angle is a strong constraint, and only a small fraction of parameter space is acceptable for attaining a strong enough phase transition for baryogenesis.
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Athron, Peter. "Aspects of electroweak symmetry breaking in physics beyond the standard model." Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/513/.
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Fine tuning in the Standard Model (SM) is the basis for a widespread expectation that the minimal model for electroweak symmetry breaking, with a single Higgs boson, is not realised in nature and that new physics, in addition to (or instead of) the Higgs, will be discovered at the Large Hadron Collider (LHC). However constraints on new physics indicate that many models which go beyond the SM (BSM) may also be fine tuned (although to a much lesser extent). To test this a reliable, quantitative measure of tuning is required. We review the measures of tuning used in the literature and propose an alternative measure. We apply this measure to several toy models and a constrained version of the Minimal Supersymmetric Standard Model. The Exceptional Supersymmetric Standard Model (E6SSM) is another BSM motivated by naturalness. As a supersymmetric theory it solves the SM hierarchy problem and by breaking a new gauged U(1) symmetry it also solves the μ-problem of the MSSM. We investigate the Renormalisation Group Evolution of the model and test for radiative electroweak symmetry breaking in two versions of the model with different high scale constraints. First we briefly look at scenarios with non-universal Higgs masses at the GUT scale and present a particle spectrum that could be observed at the LHC. Secondly we study the constrained E6SSM (CE6SSM), with universal scalar (m0), trilinear (A0) and gaugino (M) masses. We reveal a large volume of CE6SSM parameter space where the correct breakdown of the gauge symmetry can be achieved and all experimental constraints can be satisfied. We present benchmark points corresponding to different patterns of the particle spectrum. A general feature of the benchmark spectra is a light sector of SUSY particles consisting of a light gluino, two light neutralinos and a light chargino. Although the squarks, sleptons and Z′ boson are typically much heavier, the exotic color triplet charge 1/3 fermions as well as the lightest stop can be also relatively light leading to spectacular new physics signals at the LHC.
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Marx, Marilyn. "Standard model and exotic diboson production with the ATLAS detector." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/standard-model-and-exotic-diboson-production-with-the-atlas-detector(7a674cb6-dd88-46d3-9506-6b9f1074eac7).html.
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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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Del, Donno Antonio. "Testing electroweak baryogenesis at LHC in a minimal extension of the Standard Model." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/17052/.
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Il modello standard è la teoria che descrive con spettacolare accuratezza le interazioni fra i costituenti fondamentali della materia come oggi ci sono noti. Nonostante il successo nel confronto fra teoria ed esperimenti, diverse questioni rimangono insolute. Indicazioni esistono riguardo l'esistenza di fisica oltre il modello standard, anche se ancora ignoriamo la sua natura. L'obiettivo principale di questo lavoro è di caratterizzare una delle più semplici estensioni del modello standard che prevede un singoletto scalare interagente con il solo bosone di Higgs. Questo nuovo stato potrebbe avere un'influenza sulla fenomenologia del bosone di Higgs ai collider e dare luogo al meccanismo della bariogenesi elettrodebole. Una volta classificate le differenti possibilità, concentriamo la nostra attenzione su un modello semplificato caratterizzato da una simmetria $\mathbb{Z}_{2}$, nel quale le modifiche al self-coupling del bosone di Higgs possono apparire solo ad un loop. Il calcolo dei contributi corrispondenti permette di identificare la regione dello spazio dei parametri dove è possibile ottenere una transizione di fase elettrodebole del primo ordine, e di verificare se le deviazioni dalle previsioni del modello standard possano essere rilevabili ad LHC. Consideriamo sia il modello completo che la corrispondente approssimazione effettiva, studiandone il regime di applicabilità. Infine, otteniamo le previsioni per la produzione di una coppia di bosoni di Higgs. I nostri risultati preliminari mostrano come nelle regioni dello spazio dei parametri nelle quali è possibile avere la transizione del primo ordine un approccio effettivo sia sufficiente a riprodurre il modello completo. Inoltre, le differenze di shape e sezione d'urto fra la estensione con un singoletto ed il modello standard sono visibili per valori della massa del singoletto potenzialmente rilevabili a LHC.
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Tayduganov, Andrey. "Electroweak radiative B-decays as a test of the Standard Model and beyond." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00648217.
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Recently the radiative B-decay to strange axial-vector mesons, B--> K1(1270) gamma, was observed with a rather large branching ratio. This process is particularly interesting as the subsequent K1-decay into its three-body final state allows us to determine the polarization of the photon, which is mostly left(right)-handed for Bbar(B) in the Standard Model while various new physics models predict additional right(left)-handed components. In this thesis, a new method is proposed to determine the polarization, exploiting the full Dalitz plot distribution, which seems to reduce significantly the statistical errors on the polarization parameter lambda_gamma measurement.This polarization measurement requires, however a detailed knowledge of the K1--> K pi pi strong interaction decays, namely, the complex pattern of the various partial wave amplitudes into several possible quasi-two-body channels as well as their relative phases. A number of experiments have been done to extract all these information while there remain various problems in the previous studies. In this thesis, we investigate the details of these problems. As a theoretical tool, we use the 3P0 quark-pair-creation model in order to improve our understanding of strong K1 decays.Finally we try to estimate some theoretical uncertainties: in particular, the one coming from the uncertainty on the K1 mixing angle, and the effect of a possible ''off-set'' phase in strong decay S-waves. According to our estimations, the systematic errors are found to be of the order of sigma(lambda_gamma)^th<20%. On the other hand, we discuss the sensitivity of the future experiments, namely the SuperB factories and LHCb, to lambda_gamma. Naively estimating the annual signal yields, we found the statistical error of the new method to be sigma(lambda_gamma)^stat<10% which turns out to be reduced by a factor 2 with respect to using the simple angular distribution.We also discuss a comparison to the other methods of the polarization measurement using processes, such as B--> K* e^+ e^-, Bd--> K* gamma and Bs--> phi gamma, for the determination of the ratio of the Wilson coefficients C7gamma^'eff/C7gamma^eff. We show an example of the potential constraints on C7gamma^'eff/C7gamma^eff. in several scenarios of supersymmetric models.
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Lyonnet, Florian. "New heavy resonances : from the electroweak to the planck scale." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY035/document.
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Le principe d'invariance de jauge local est au centre de la physique des particules moderne. Dans le modèle standard (MS), il repose sur le groupe de jauge ad hoc SU(3)_c x SU(2)_L x U(1)_Y. L'idée d'étendre ce groupe de jauge est particulièrement attrayante dans une perspective de ``Grand Unified Theory'' (GUT) où le MS est la limite basse énergie d'une théorie plus fondamentale basée sur un groupe de jauge beaucoup plus large tel que SO(10) ou E(6). En effet, lors de la brisure de symétrie du groupe de GUT au MS, des facteurs de groupe non-brisés supplémentaires, tels que U(1) ou SU(2), peuvent apparaitre. Ce manuscrit est consacré à la phénoménologie de modèles avec un groupe de jauge étendu. En particulier, les études présentées sont centrées sur les modèles basés sur le groupe de jauge SU(2) x SU(2) x U(1) dénotés G(221). De manière générique, ces modèles prédisent de nouveaux bosons de jauges, Z' et W'.Après une brève présentation des modèles G(221), un nouveau code publique, PyR@TE, qui permet de déterminer les équations du groupe de renormalisation à deux boucles pour une théorie de jauge arbitraire est introduit. Ce code est ensuite utilisé pour déterminer les RGEs des modèles de la classe G(221). La suite du manuscrit est dédiée à la présentation des résultats obtenus sur le calcul des corrections radiatives QCD de la production électrofaible d'une paire de quarks top dans le cadre des modèles G(221), i.e. en présence d'un nouveau boson de jauge Z'. Ces résultats font l'objet d'une implémentation dans le générateur d'événements Monte Carlo POWHEG BOX et les premiers résultats numériques obtenus sont présentés. Les derniers développements concernant le calcul des corrections QCD à la production électrofaible de single-top sont également revus. Enfin, la dernière partie de ce manuscrit est consacrée à l'étude de l'impact de nouvelles résonances W', Z', telles que celles présentes dans les modèles G(221), sur l'interaction des neutrinos d'ultra-haute énergie dans l'atmosphère. Ces interactions sont recherchées par l'observatoire Pierre Auger dans les douches de particules produites par l'interaction des rayons cosmiques avec les particules de l'atmosphèreThe principle of local gauge invariance is a pillar of modern particle physics theories and in the SM relies on the ad-hoc gauge group structure SU(3)_c x SU(2)_L x U(1)_Y. Extending this gauge group is very well motivated in a Grand Unified Theory (GUT) perspective in which the SM is the low-energy limit of a more fundamental theory based on a larger gauge group like SO(10) or E(6). Indeed, the symmetry breaking (SB) of the underlying GUT gauge group, down to the SM one, leaves some additional group factors unbroken, such as U(1) or SU(2). In this spirit, we focus in this manuscript on the phenomenology of extended gauge group models and on the new heavy neutral and charged resonances, generically called Z' and W' predicted by these.In this manuscript we present different aspects of the phenomenology of the G(221) models. After reviewing these extensions, we present a public tool, PyR@TE, that aims at automating the calculation of RGEs at two-loop for arbitrary gauge theories and exemplify its use with the G(221) models. In a second part, we present our results for the calculation of the QCD corrections to the electroweak top-pair production as well as their implementation in a general purpose Monte Carlo generator allowing for a consistent matching of next-to-leading order (NLO) matrix elements with parton shower algorithms, the POWHEG BOX. We then review the status of our calculation of the QCD corrections to the electroweak single-top production. Finally, we present a different aspect of the phenomenology of new heavy resonances, Z', W' by studying their impact on the interaction of ultra-high energy neutrinos in the atmosphere. For definiteness we consider the Pierre Auger Observatory, which is sensible to showers initiated by neutrinos of extreme energies up to 10E12 GeV
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Xue, Ying. "Quantum field-theoretical investigations in nonperturbative QCD and beyond-the-standard-model electroweak physics." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0012/NQ31168.pdf.
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Rank, Jörn [Verfasser]. "Thermal Screening Masses in the Standard Model of Strong and Electroweak Interactions / Jörn Rank." Bielefeld : Universitätsbibliothek Bielefeld, 1998. http://d-nb.info/1034401319/34.
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Konstandin, Thomas. "CP-violation and baryogenesis on electroweak scales cosmological predictions for the standard model and beyond /." [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975800280.
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Carrington, James Michael. "Vacuum stability of the standard model and BSM extensions." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8851.
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The Standard Model scalar potential contains a minimum at the Electroweak scale, responsible for the masses of the weak gauge bosons through the Higgs mechanism. However, if the Electroweak minimum is only a local minimum, and there exists a global minimum at a higher energy in the Higgs potential, then in a su ciently old universe we would expect the vacuum expectation value to be at the global minimum. The absence of a global minimum at higher energy is related to the condition that the Higgs self coupling is greater than or equal to zero for all energies. For any model that fails this, we expect new physics to enter before the energy at which the coupling becomes negative. We developed tools to automate the derivation of beta functions for renormalisable gauge theories, and used these to carry out evolution of the renormalisation group equations for the Standard Model and three extensions to the Standard Model | the Standard Model with a fourth generation, the Standard Model with right-handed neutrinos and a Left-Right Symmetric Model. We conclude that of these four models, the Standard Model is the only one in which all the couplings remain perturbative, and in which the Electroweak minimum is a global minimum.
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Papucci, Michele. "Electroweak Symmetry Breaking with a compact extra dimension." Doctoral thesis, Scuola Normale Superiore, 2009. http://hdl.handle.net/11384/85837.
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[Excerpt from the preface]: During my Ph.D. course, under the supervision of Riccardo Barbieri, I started
working on Theoretical High Energy Physics. In particular I focused on the problem
of Electroweak Symmetry Breaking and in this context I investigated the
bene ts of introducing a compact extra dimension.
In a series of papers, together with Riccardo Barbieri, Guido Marandella,
Lawrence Hall, Yasunori Nomura, Takemichi Okui and Steven Oliver I built supersymmetric
models in 5D and studied their phenomenology in detail [1, 2, 3, 4].
In this models Supersymmetry is broken by boundary conditions in the fth dimension
and the ElectroWeak Symmetry Breaking is triggered by Supersymmetry
breaking via the top/stop radiative corrections. The phenomenology of these models
is signi cantly di erent than the one of the Minimal Supersymmetric Standard
Model scenarios extensively studied in the literature.
These papers constitute the subject of this Thesis and their results will be
presented in the following Chapters.
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Dartsi, Olympia. "Recherche de la production électrofaible de paires Zγ et mesure de la section efficace différentielle de production de Zγ en association avec deux jets dans l'ATLAS expérience du LHC." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY085.
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Le sujet physique de ma thèse est la mesure de la section efficace de di-boson Zgamma; production en association avec une paire de dijet à haute masse.Les données de collision protons-protons de l’expérience ATLAS au Grand collisionneur de hadrons du CERN à une énergie dans le centre de masse de13 TeV, recueillies en 2015 et 2016 et correspondant à une luminosité intégrée de 36.1 fb^{-1} sont analysées. La production électrofaible d’événements Zgammajj donne un accès direct à la nature du mécanisme de brisure spontanée de symétrie électrofaible, en sondant les couplages quantiques de boson WWZgamma,ZZZgamma, ZZgammagamma et Zgammagammagamma. Les trois derniers sont interdits à l’ordre le plus basdans le Modèle Standard. Tout écart par rapport aux prévisions du ModèleStandard pourrait être un indice d’une nouvelle physique.Jusqu’à présent, la production électrofaible de Zgammajj, qui consiste en desprocessus avec constante couplage électrofaible du quatrième ordre et qui inclut des processus de diffusion de vecteur-boson, n’a jamais été observée. Le même état final Zgammajj peut être produit par un processus fortement médié,avec un constante couplage électrofaible de second ordre et un couplage fortde second ordre, résultant en une section efficace de trois ordres de grandeur plus grande que la section électrofaible. La production de Zgammajj via un mécanisme électrofaible et fort interfère puisque les états initiaux et finaux sont les mêmes. La compréhension de cet effet est un aspect important de l’analyse.Dans ma thèse, j’ai étudié cet effet et son impact sur l’observation du pro-cessus et sur les mesures de le section efficace. Pour cette étude, après avoir effectué le calcul des trois contributions (électrofaible, forte et interférence) à la section efficace totale à l’aide de simulations de Monte Carlo, j’ai effectué une optimisation des coupes de sélection, afin de réduire l’impact de l’interférence, en définissant également une procédure pour la prise en compte de cette interférence dans l’analyse des données. Le point focal expérimental de mon travail est la mesure de la section efficace différentielle de l’état final Zgammajj en fonction de la masse invariante du système Zgamma, du momentum transversal du photon, de la multiplicité de jets et de la masse invariante du système Dijet. Les distributions sensibles à la nouvelle physique sont corrigées par les effets détecteur et comparées aux attentes des PM.Tous résultat de physique repose sur la reconstruction et la sélection d’états finaux composés de jets, d’électrons, de muons et de photons. Les électrons et leur identification jouent donc un rôle important dans l’analyse Zgammajj. Ce rapport de thèse documente également le travail que j’ai fait sur l’efficacité de l’identification des électrons, y compris d’une méthode supplémentaire axée sur les données. Les résultats que j’ai obtenus, sont utilisés dans toutes les analyses ATLAS dont la signature contient des électronsThe physics subject of my thesis work, is the measurement of the cross-section of the diboson Zgamma production in association with a high mass dijetsystem. Proton-proton collision data from the ATLAS experiment at theCERN Large Hadron Collider at a center-of-mass energy of 13 TeV,collected in 2015 and 2016 and corresponding to an integrated luminosity of36.1 fb^{-1} are analyzed. The electroweak production of Zgammajj events, provides a direct access to the nature of the electroweak symmetry breaking mechanism, by probing the quantum gauge boson couplings WWZgamma, ZZZgamma, ZZgammagamma and Zgammagammagamma. The last three are forbidden at the lowest order in the Standard Model. Any deviation from the Standard Model predictions could be a hint for new physics.Until now, the electroweak production of Zgammajj, which consist in pro-cesses with fourth-order electroweak coupling and include vector-boson scat-tering processes, has never been observed. The same Zgammajj final state canbe produced by a strongly-mediated process, with second order electroweakcoupling and second order strong coupling, resulting in a cross-section threeorder of magnitude larger than the electroweak cross-section. The Zgammajj pro-duction via electroweak and strong mechanism interfere since the initial andfinal states are the same. The understanding of this effect is an importantaspect of the analysis.In my thesis, I have studied this effect and its impact on the observationof the process and on the fiducial cross-section measurements. For this inves-tigation, after having performed the computation of the three contributions(electroweak, strong and interference) to the total cross-section using MonteCarlo simulations I have performed an optimization of the selection cuts, in order to reduce the impact of the interference, defining also a procedure onhow to account for the interference in the data analysis. The experimentalfocus of my work is the measurement of the differential cross section of theZgammajj final state as function of the invariant mass of the Zgamma system, the transverse momentum of the photon, the jet multiplicity and the invariantmass of the dijet system. Distributions sensitive to new physics are unfoldedand compared with MC expectations.All physics results rely on the reconstruction and selection of final statesconsisting of jets, electrons, muon and photons. Electrons and their identi-fication therefore play an important role in the Zgammajj analysis. This thesisreport documents also the work that I have done on the electron identification efficiency, including the implementation of an additional data drivenmethod. The results I have obtained, are used in all ATLAS analyses whosesignature contain electrons
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Gadfort, Thomas. "Evidence for electroweak top quark production in proton-antiproton collisions at sqrt(s) = 1.96 TeV /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/9684.
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Humbert, Pascal [Verfasser], and Manfred [Akademischer Betreuer] Lindner. "Alternative Electroweak Symmetry Breaking based on Conformal Extensions of the Standard Model / Pascal Humbert ; Betreuer: Manfred Lindner." Heidelberg : Universitätsbibliothek Heidelberg, 2016. http://d-nb.info/1180616472/34.
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Lee, Christopher Wise Mark B. "Probing physics in the standard model and beyond with electroweak baryogenesis and effective theories of the strong interactions /." Diss., Pasadena, Calif. : California Institute of Technology, 2005. http://resolver.caltech.edu/CaltechETD:etd-05272005-162229.
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Feigl, Bastian [Verfasser], and D. [Akademischer Betreuer] Zeppenfeld. "Electroweak Processes in the Standard Model and Beyond: Backgrounds to Higgs Physics and Semileptonic Decay Modes / Bastian Feigl. Betreuer: D. Zeppenfeld." Karlsruhe : KIT-Bibliothek, 2013. http://d-nb.info/1044956194/34.
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CETORELLI, FLAVIA. "First observation of the electroweak production of a W+W- pair in association with two jets in the fully leptonic channel with the CMS detector at the LHC." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2022. http://hdl.handle.net/10281/369032.
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Questa tesi riporta la prima osservazione della produzione elettrodebole di una coppia di bosoni W+W- in associazione con due jet nello stato finale leptonico.
L’analisi è stata svolta sui dati raccolti dal rivelatore CMS durante le collisioni p-p ad un’energia del centro di massa di 13 TeV, che si sono svolte al Large Hadron Collider (LHC) nel periodo 2016-2018.
La produzione elettrodebole di due bosoni W+W- appartiene alla classe dei processi rari di vector boson scattering (VBS). Lo studio di processi VBS è uno degli obiettivi centrali di LHC, poiché sono direttamente connessi al bosone di Higgs e al processo di rottura spontanea della simmetria elettrodebole.
Gli eventi sono stati selezionati chiedendo la presenza di due leptoni (e/μ) con carica di segno opposto, due jet con grande massa invariante e grande separazione in pseudorapidità, e una quantità di momento trasverso mancante. Gli eventi sono divisi in categorie rispetto al sapore dei leptoni carichi nello stato finale: ee, μμ, and eμ.
La produzione di ttbar-tW costituisce il maggior fondo dell’analisi. Un’altra fonte importante di fondo è data dai diagrammi con due vertici QCD, che producono lo stesso stato finale del segnale (produzione QCD di W+W-). La produzione Drell-Yan (DY) contamina principalmente gli stati finali con due elettroni o due muoni, mentre è fortemente soppressa nello stato finale eμ.
Una deep neural network (DNN) è stata allenata per separare il segnale dai fondi ttbar e QCD W+W- nello stato finale eμ. L’uso dell’output della DNN come variabile discriminante in questa categoria ha migliorato le performance dell’analisi.
L’analisi riporta l’osservazione del processo elettrodebole di produzione di bosoni W+W- con una significatività statistica di 5.6 deviazioni standard.
Inoltre, si riporta la prima misura di sezione d’urto del processo in due spazi fiduciali differenti. Il primo è uno spazio fiduciale inclusivo, definito con tagli su variabili a parton level sui partoni uscenti: si richiede che abbiano pT > 10 GeV e massa invariante mqq > 100 GeV. La sezione d’urto misurata nello spazio fiduciale inclusivo è 99 ± 20 fb, da confrontare con l’attesa teorica LO di 89 ± 5 fb. Il secondo è un volume esclusivo, definito con selezioni sugli osservabili a livello generatore che copiano quelle della regione di segnale dell’analisi. In questo volume fiduciale, la sezione d’urto osservata è 10.2 ± 2.0 fb, mentre quella attesa è 9.1 ± 0.6 fb. I risultati osservati sono in accordo con le previsioni dello standard model.
Questa tesi riporta inoltre il lavoro per la calibrazione del calorimetro elettromagnetico (ECAL).
Il metodo EFlow, sviluppato durante questo lavoro, produce intercalibrazioni con una granularità spaziale del singolo cristallo e temporale di 1-2 giorni, che correggono la perdita residua di risposta in luce dei cristalli.
Il metodo si basa sull’uso di eventi minimum bias provenienti dalle collisioni soft di LHC, come il metodo φ-symmetry. Questi eventi hanno una distribuzione uniforme in φ che può essere sfruttata per calibrare il detector.
Il metodo EFlow sviluppa ed estende l’idea del metodo φ-symmetry, normalizzando l’energia di ogni cristallo a quella media del barrel. In questo modo, la risposta di ogni cristallo è adattata alla perdita media del barrel. Gli eventi con elettroni dal decadimento di bosoni W/Z sono utilizzati per correggere la perdita residua globale del barrel.
Le correzioni sono competitive con quelle ottenute dal metodo utilizzato durante il Run II, che usava la distribuzione E/p degli elettroni dai decadimenti dei bosoni W/Z.
Il metodo EFlow sarà implementato durante Run III per effettuare la calibrazione “prompt” dei dati, poiché garantisce la necessaria finezza spaziale e temporale delle intercalibrazioni.This thesis reports the first observation of the electroweak production of a W+W- pair of bosons in association with two jets in the fully leptonic final state. The analysis has been performed using the data sample collected by the CMS detector during the 2016-2018 p-p collisions at center-of-mass energy of 13 TeV, provided by the Large Hadron Collider (LHC). The electroweak W+W- production belongs to the very rare class of vector boson scattering (VBS) processes, which are purely electroweak at tree level. The investigation of VBS processes is a central objective of the LHC since they are connected directly to the Higgs boson and the spontaneous symmetry breaking mechanism of the electroweak interaction. The events were selected requiring the presence of two leptons (eμ) with opposite sign charges, two jets with large invariant mass and large pseudorapidity separation, and a certain amount of missing transverse momentum. Events are then separated into different categories considering the flavor of the charged leptons: ee, μμ, and eμ. The ttbar-tW productions constitute the main background of the analysis. Another important source of background is due to diagrams containing two QCD vertices, which produce the same final state as the signal (QCD-induced W+W- production). The Drell-Yan (DY) production contaminates the ee and μμ final states, while this background is highly suppressed in the eμ one. A deep neural network (DNN) was trained to separate the signal from the ttbar and the QCD-induced W+W- production in the eμ final state. The use of the DNN output as a discriminator in this category has boosted the performance of the analysis. Finally, the analysis reaches the observation of the electroweak W+W- signal with a statistical significance of 5.6 standard deviations, whereas 5.2 standard deviations were expected. Moreover, two cross sections are measured into two different fiducial phase spaces. The first one is an inclusive phase space, defined with cuts at parton level on the two outgoing partons: they are required to have a pT > 10 GeV and an invariant mass mqq > 100 GeV. The measured cross section in the inclusive phase space is 99 ± 20 fb to be compared with the theoretical expectation at the lowest order of 89 ± 5 fb. The second one is an exclusive volume, defined with requirements on observables at generator level that mimic the ones of the analysis signal region. In this fiducial volume, the cross section observed is 10.2 ± 2.0 fb, while the expected one is 9.1 ± 0.6 fb. These are the first measurements of the purely electroweak W+W- cross section; the results show good agreement with standard model expectations. The thesis also reports the work for the electromagnetic calorimeter (ECAL) calibration. The EFlow method, developed during this work, provides per-crystal intercalibration with a time granularity of about 1-2 days to correct the time drift in light response that is still visible after laser corrections. The method relies on the use of minimum bias events from soft collisions, as the φ-symmetry method, which are expected to have a uniform distribution in φ. The EFlow extends the idea of the φ-symmetry method, normalizing the energy of each crystal to the mean of the barrel. In this way, the response in time of each crystal is adjusted to the average drift of the barrel. The events with electrons from W and Z decays are used to correct the residual global drift. The corrections derived in this way are competitive with ones obtained by the method employed during Run II, which used the E/p distribution of electrons from W and Z decays. Thanks to the fine space-time granularity of these corrections and the rapidity of deriving them, the method may be implemented in Run III to provide the so-called “prompt” calibrations for the ECAL.
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Lee, Jae Yong. "The little Higgs and some phenomenology /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9645.
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Suster, Carl Joseph Edmund. "Cross-section measurements of the electroweak production of a single top quark in association with a W boson at √s = 13 TeV with the ATLAS detector." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21615.
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The top quark is the most massive fundamental particle within the Standard Model of particle physics, discovered at Fermilab in 1995. In pp collisions at the Large Hadron Collider at CERN, large quantities of top quarks are produced, offering the first opportunity to explore its properties in rarer production modes in detail. This thesis presents measurements of the cross-section of the electroweak production of a single top quark in association with a W boson, using data collected at 13 TeV centre-of-mass energy with the ATLAS detector. The total tW production cross-section is measured in events with two oppositely-charged electrons or muons. Differential tW cross-sections are measured with respect to several observables, providing the first detailed validation of the modelling of the process. The measurements are consistent with theoretical predictions, and contribute to future improvements in the modelling of tW production.
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Becker, Sebastian. "Estimation of standard model backgrounds to the search for electroweak production of supersymmetry in events with at least two tau leptons in the final state." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-162539.
Full textAbstract:
This thesis presents a search for Supersymmetry in events with at least two hadronically decaying tau leptons and missing transverse energy. The ana\-lysis is focused on the electro-weak production of gaugino pairs. Electroweak production processes for SUSY particles are promising candidates for the discovery of Supersymmetry with $R$-parity conservation at hadron-hadron colliders.
For the analysis a sample of proton-proton collisions at a center of mass energy of $\sqrt{s}=\unit[8]{TeV}$ with an integrated luminosity of $\int {\cal L}~\mathrm{dt}= \unit[20.3]{fb^{-1}}$ is used. The collisions have been recorded with the ATLAS detector at the LHC in the year 2012.
In two different selections the Standard Model predictions are compared with the observations. The observation of 6 events in the first selection and 14 in the second does not deviate significantly from the Standard Model with an expectation of 11 events in the first selection and 17 in the second.
These results are interpreted in a phenomenological Minimal Supersymmetric Standard Model and in simplified models. For a simplified model with a chargino-neutralino pair production scenario the parameter space for masses of the lightest neutralino up to $\unit[100]{GeV}$ and up to $\unit[350]{GeV}$ for the lightest chargino mass can be excluded.
For a simplified model with chargino pair production processes the parameter space for the lightest neutralino mass up to $30-\unit[50]{GeV}$ in a range for the lightest chargino mass of $170-\unit[330]{GeV}$ can be excluded.
This thesis is focused on the estimation techniques of Standard Model background processes. Different methods for the estimation of the background originating from $Z$-boson and top-quark decays are investigated.In dieser Arbeit wird eine Suche nach Supersymmetrie für Ereignisse mit zwei hadronisch zerfallenden Tau Leptonen und fehlender Transversalenergie im Endzustand präsentiert. Die Analyse konzentriert sich dabei auf die elektroschwache Produktion von Gaugino Paaren. Elektroschwache Produktions\-prozesse sind vielversprechende Kandidaten für die Entdeckung der Supersymmetrie mit $R$-Paritätserhaltung an Hadron-Hadron Teilchenbeschleuni\-gern. Für die Analyse wurde ein Datensatz von Proton-Proton Kollisionen bei einer Schwerpunktenergie von $\sqrt{s}=\unit[8]{TeV}$ mit einer integrierten Luminosität von $\int {\cal L}~\mathrm{dt}= \unit[20.3]{fb^{-1}}$ verwendet. Die Daten wurden mit dem ATLAS Detektor am LHC im Jahr 2012 aufgezeichnet. Die beobachteten Datenereignisse wurden mit den Vorhersagen des Standardmodells für zwei unterschiedliche Sätze von Signalauswahlkriterien verglichen. Die Beobachtung von 6 Ereignissen in der ersten Signalregion und 14 Ereignissen in der zweiten weicht nicht signifikant von den Vorhersagen des Standardmodells mit 11 Ereignissen in der ersten Signalregion und 17 in der zweiten ab. Diese Ergebnisse wurden mit Hinblick auf ein phänomenologisches minimal supersymmetrisches Standardmodell und auf vereinfachte supersymmetrische Modelle interpretiert. Für ein vereinfachtes Modell mit Chargino-Neutralino Paarproduktion kann der Parameterraum für Massen des leichtesten Neutralinos bis zu $\unit[100]{GeV}$ und bis zu $\unit[350]{GeV}$ für die Masse des leichtesten Charginos ausgeschlossen werden. Für ein vereinfachtes Mo\-dell mit Chargino Paarproduktion kann der Parameterraum für die leichteste Neutralinomasse bis zu $30-\unit[50]{GeV}$ in einem Bereich der leichtesten Chargino Masse von $170-\unit[330]{GeV}$ ausgeschlossen werden. Das Hauptaugenmerk dieser Arbeit liegt jedoch auf den Verfahren, die zur Bestimmung des Standardmodell-Untergrundes benutzt werden. Unterschiedliche Methoden zur Bestimmung des Untergrunds aus $Z$-Boson und Top-Quark Zerfallsprozessen wurden untersucht.
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Becker, Sebastian [Verfasser], and Dorothee [Akademischer Betreuer] Schaile. "Estimation of standard model backgrounds to the search for electroweak production of supersymmetry in events with at least two tau leptons in the final state / Sebastian Becker. Betreuer: Dorothee Schaile." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2013. http://d-nb.info/1044532319/34.
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Zeman, Martin. "Measurement of the Standard Model W⁺W⁻ production cross-section using the ATLAS experiment on the LHC." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112263/document.
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Les mesures de sections efficaces de production di-bosons constituent une partie importante du programme de physique au Large Hadron Collider (Grand collisionneur de hadrons) au CERN. Ces analyses de physique offrent la possibilité d'explorer le secteur électrofaible du modèle standard à l'échelle du TeV et peuvent être une indication de l'existence de nouvelles particules au-delà du modèle standard. L'excellente performance du LHC dans les années 2011 et 2012 a permis de faire les mesures très compétitives. La thèse donne un aperçu complet des méthodes expérimentales utilisées dans la mesure de la section efficace de production de W⁺W⁻ dans les collisions proton-proton au √s = 7 TeV et 8 TeV. Le texte décrit l'analyse en détail, en commençant par l'introduction du cadre théorique du modèle standard et se poursuit avec une discussion détaillée des méthodes utilisées dans l'enregistrement et la reconstruction des événements de physique dans une expérience de cette ampleur. Les logiciels associés (online et offline) sont inclus dans la discussion. Les expériences sont décrites en détail avec en particulier une section détaillée sur le détecteur ATLAS. Le dernier chapitre de cette thèse présente une description détaillée de l'analyse de la production de bosons W dans les modes de désintégration leptoniques utilisant les données enregistrées par l'expérience ATLAS pendant les années 2011 et 2012 (Run I). Les analyses utilisent 4,6 fb⁻¹ de données enregistrées à √s = 7 TeV et 20,28 fb⁻¹ enregistré à 8 TeV. La section efficace mesurée expérimentalement pour la production de bosons W dans l'expérience ATLAS est plus grande que celle prédite par le modèle standard à 7 TeV et 8 TeV. La thèse se termine par la présentation des résultats de mesures différentielles de section efficaceMeasurements of di-boson production cross-sections are an important part of the physics programme at the CERN Large Hadron Collider. These physics analyses provide the opportunity to probe the electroweak sector of the Standard Model at the TeV scale and could also indicate the existence of new particles or probe beyond the Standard Model physics. The excellent performance of the LHC through years 2011 and 2012 allowed for very competitive measurements. This thesis provides a comprehensive overview of the experimental considerations and methods used in the measurement of the W⁺W⁻ production cross-section in proton-proton collisions at √s = 7 TeV and 8 TeV. The treatise covers the material in great detail, starting with the introduction of the theoretical framework of the Standard Model and follows with an extensive discussion of the methods implemented in recording and reconstructing physics events in an experiment of this magnitude. The associated online and offline software tools are included in the discussion. The relevant experiments are covered, including a very detailed section about the ATLAS detector. The final chapter of this thesis contains a detailed description of the analysis of the W-pair production in the leptonic decay channels using the datasets recorded by the ATLAS experiment during 2011 and 2012 (Run I). The analyses use 4.60 fb⁻¹ recorded at √s = 7 TeV and 20.28 fb⁻¹ recorded at 8 TeV. The experimentally measured cross section for the production of W bosons at the ATLAS experiment is consistently enhanced compared to the predictions of the Standard Model at centre-of-mass energies of 7 TeV and 8 TeV. The thesis concludes with the presentation of differential cross-section measurement results
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Buttazzo, Dario. "Implications of the discovery of a Higgs boson with a mass of 125 GeV." Doctoral thesis, Scuola Normale Superiore, 2013. http://hdl.handle.net/11384/85868.
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The discovery of a Higgs-like particle by the ATLAS and CMS experiments at the LHC
has been a major event for particle physics. The rather precise knowledge of the mass of
the Higgs boson and of its couplings to the other Standard Model elds has important
consequences for the physical phenomena taking place at the Fermi scale of electroweak
symmetry breaking. We will analyze some of these implications in the most motivated
frameworks for physics at that scale { supersymmetry, models of a composite Higgs boson,
and the Standard Model itself.
At the same time, precision experiments in
avour physics require a highly non-generic
structure of
avour and CP transitions. This is relevant to any model of electroweak
symmetry breaking with a relatively low scale of new phenomena, motivated by naturalness,
where some mechanism has to be found in order to keep unwanted
avour e ects
under control. We will discuss in particular the consequences of the approximate U(2)3
symmetry exhibited by the quarks of the Standard Model.
The combined analysis of the indirect constraints from
avour, Higgs and electroweak
physics will allow us to outline a picture of some most natural models of physics at the
Fermi scale. This is particularly interesting in view of the forthcoming improvements in
the direct experimental investigation of the phenomena at that energies. Although non
trivially, a few models emerge that look capable of accommodating a 125 GeV Higgs
boson, consistently with all the other constraints, with new particles in an interesting
mass range for discovery at the LHC, as well as associated
avour signals.
Finally, the measurement of the last parameter of the Standard Model { the Higgs quartic
coupling { has important consequences even if no new physics is present close to the Fermi
scale: its near-critical value, which puts the electroweak vacuum in a metastable state
close to a phase transition, may have an interesting connection with Planck-scale physics.
We derive the bound for vacuum stability with full two-loop precision and use it to explore
some possible scenarios of near-criticality.
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Gumpert, Christian. "Measurement of Electroweak Gauge Boson Scattering in the Channel pp → W ± W ± jj with the ATLAS Detector at the Large Hadron Collider." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-162847.
Full textAbstract:
Particle physics deals with the elementary constituents of our universe and their interactions. The electroweak symmetry breaking mechanism in the Standard Model of Particle Physics is of paramount importance and it plays a central role in the physics programmes of current high-energy physics experiments at the Large Hadron Collider. The study of scattering processes of massive electroweak gauge bosons provides an approach complementary to the precise measurement of the properties of the recently discovered Higgs boson. Owing to the unprecedented energies achieved in proton-proton collisions at the Large Hadron Collider and the large amount of data collected, experimental studies of these processes become feasible for the first time. Especially the scattering of two W± bosons of identical electric charge is considered a promising process for an initial study due to its distinct experimental signature. In the course of this work, 20.3 fb−1 of proton-proton collision data recorded by the ATLAS detector at a centre-of-mass energy of √s = 8 TeV are analysed. An analysis of the production of two W± bosons of identical electric charge in association with two jets, pp → W ± W ± jj, is conducted in the leptonic decay channel of the W± bosons.
Thereby, emphasis is put on the development of methods for the estimation of experimental backgrounds as well as on the optimisation of the event selection. As a result of this work, first experimental evidence for the existence of the aforementioned process is established with an observed significance of 4.9. Based on the number of observed events in the selected phase space the extracted fiducial cross section is σ(fid) = (2.3 ± 0.5(stat.) +0.4/−0.3 (sys.)) fb which is in agreement with the prediction of the Standard Model of σ(fid,SM) = (1.6 ± 0.2) fb. Of particular theoretical interest are electroweak contributions to the pp → W ± W ± jj process due to their sensitivity to the nature of the electroweak symmetry breaking mechanism. Criteria for a dedicated event selection are investigated and implemented in the analysis with the goal of enhancing the sensitivity to these contributions. First experimental evidence for the presence of electroweak contributions to the pp → W ± W ± jj process can be claimed with an observed significance of 4.1. The cross section extracted in the selected phase space region is found to be σ(fid) = (1.7 +0.5/−0.4 (stat.) ± 0.3(sys.)) fb which is 1.3 standard deviations above the theoretical prediction of the Standard Model of σ(fid,SM) = (1.0 ± 0.1) fb.
A variety of extensions to the Standard Model predict modifications to the electroweak gauge sector. In the context of the electroweak chiral Lagrangian, which serves as an effective approximation of these theories in the energy regime E = 1 − 3 TeV, anomalous contributions to the quartic WWWW gauge coupling can be described by the parameters α4 and α5 . The selection of events is optimised again to enhance the sensitivity to these two parameters. On the basis of the number of events observed in this phase space region, the following one-dimensional confidence intervals at the 95% confidence level are derived: −0.09 ≤ α4 ≤ 0.10 and −0.15 ≤ α5 ≤ 0.15. At present, these limits represent the most stringent constraints on contributions from new physics processes to the quartic WWWW gauge coupling.
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Khandoga, Mykola. "Calibration of electron shower shapes, hadronic recoil reconstruction using deep learning algorithms and the measurement of W boson transverse momentum distribution with the ATLAS detector." Thesis, université Paris-Saclay, 2020. https://tel.archives-ouvertes.fr/tel-03143181.
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La première partie de la thèse contient une description de la méthode d'étalonnage du calorimètre électromagnétique, corrigeant les différences entre les données et la simulation pour ce qui concerne le développement des cascades électromagnétiques dans le calorimètre. La méthode améliore l'identification des électrons et réduit l'incertitude systématique associée. La majeure partie de la thèse est consacrée à la mesure précise du spectre en impulsion transverse (pT) du boson W à l'aide des données collectées par l'expérience ATLAS à des énergies dans le centre de masse de 5 et 13 TeV lors de deux prises de données spéciales, à faible taux d’empilement, en 2017 et en 2018. La motivation pour la mesure précise du spectre en impulsion transverse du boson W est double. Premièrement, elle sert de test pour les prédictions théoriques obtenues dans le cadre du Modèle Standard et permet de comparer les performances des générateurs Monte-Carlo (MC). La deuxième raison est que ce spectre est un ingrédient à la mesure de la masse du boson W, qui est un paramètre du Modèle Standard. L'utilisation de données à faible taux d'empilement permet de réduire significativement l'incertitude systématique due au recul hadronique et améliore de ce fait la précision sur la mesure du spectre. La thèse décrit la méthodologie de la mesure du spectre en pT du boson W ainsi que les étalonnages appliqués, les corrections et les incertitudes associées. Le résultat final est obtenu à partir du recul hadronique mesuré à l'aide d'une procédure de déconvolution des effets de détecteur et est comparé aux prédictions théoriques obtenues avec différents générateurs Monte-Carlo. Une méthode alternative pour la reconstruction du recul hadronique, avec l'utilisation de réseaux neuronaux profonds est proposée dans la thèse. Il y est montré que cette méthode améliore la résolution du recul hadronique mesuré d'environ 10% dans la région la plus pertinente, de faible pT. Les observables obtenus par cette approche améliorent la sensibilité à la masse du boson WThe initial part of the thesis contains the description of the method for electromagnetic calorimeter calibration, correcting for the Data-MC discrepancy in the development of the electromagnetic showers in the calorimeter. The method improves electron identification and reduces the associated systematic uncertainty.The major part of the thesis is dedicated to the precise measurement of the W boson transverse spectrum using the data, collected by the ATLAS experiment at the energies of 5 and 13 TeV during two special low pile-up runs in 2017 and 2018. The motivation for the precise measurement of the W boson transverse spectrum is twofold. First, it serves as a test for the theoretical predictions obtained within the Standard Model and allows to benchmark the performance of the Monte-Carlo (MC) generators. The second reason is because the W pT spectrum is an input component for the measurement of the W boson mass which is a Standard Model parameter. The use of low pile-up data allows to significantly reduce the hadronic recoil systematic uncertainty improving the precision of the spectrum measurement. The thesis describes the methodology of the W boson pT spectrum measurement as well as the imposed calibrations, corrections and the associated uncertainties. The final result is obtained from the measured hadronic recoil using an unfolding procedure and is compared to the theoretical predictions obtained with different Monte-Carlo generators. An alternative method for the hadronic recoil reconstruction with the use of deep neural networks is proposed in the thesis. The method is shown to improve the resolution of the measured hadronic recoil by about 10% in the most relevant region of low pT. The observables obtained using approach improve the sensitivity to the mass of the W boson
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Anger, Philipp. "Probing Electroweak Gauge Boson Scattering with the ATLAS Detector at the Large Hadron Collider." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-151612.
Full textAbstract:
Electroweak gauge bosons as central components of the Standard Model of particle physics are well understood theoretically and have been studied with high precision at past and present collider experiments. The electroweak theory predicts the existence of a scattering process of these particles consisting of contributions from triple and quartic bosonic couplings as well as Higgs boson mediated interactions. These contributions are not separable in a gauge invariant way and are only unitarized in the case of a Higgs boson as it is described by the Standard Model. The process is tied to the electroweak symmetry breaking which introduces the longitudinal modes for the massive electroweak gauge bosons. A study of this interaction is also a direct verification of the local gauge symmetry as one of the fundamental axioms of the Standard Model. With the start of the Large Hadron Collider and after collecting proton-proton collision data with an integrated luminosity of 20.3/fb at a center-of-mass energy of 8 TeV with the ATLAS detector, first-ever evidence for this process could be achieved in the context of this work.
A study of leptonically decaying WWjj, same-electric-charge diboson production in association with two jets resulted in an observation of the electroweak WWjj production with same electric charge of the W bosons, inseparably comprising WW->WW electroweak gauge boson scattering contributions, with a significance of 3.6 standard deviations. The measured production cross section is in agreement with the Standard Model prediction.
In the course of a study for leptonically decaying WZ productions, methods for background estimation, the extraction of systematic uncertainties and cross section measurements were developed. They were extended and applied to the WZjj final state whereof the purely electroweakly mediated contribution is intrinsically tied to the scattering of all Standard Model electroweak gauge bosons: Wγ->WZ and WZ->WZ. Three charged leptons and a neutrino from the decay of the final state bosons allow inferences about the scattering process. A distinct signature is provided by the two accompanying tagging jets as remnants of the incoming quarks radiating the initial electroweak gauge bosons. The cross section of the electroweak WZjj production was measured to σ(fiducial, observed) = (0.63 +0.32 -0.28 (stat.) +0.41 -0.24 (syst.)) fb and was found to be consistent with the Standard Model prediction at next-to-leading order in perturbative quantum chromodynamics, σ(fiducial, theory) = (0.31 +0.03 -0.05) fb. Unfolded differential cross sections of kinematic variables sensitive to models of new physics were derived. Anomalous quartic electroweak gauge couplings are introduced as dimensionless coupling parameters of additional operators within an effective field theory approach. Constraints on the parameters of operators with dimension eight were set employing a unitarization prescription based on form factors.
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Bey, Anissa. "Test du Modèle Standard à basse énergie : mesure précise des rapports d’embranchement de 62 Ga : mesure précise de la durée de vie de 38 Ca." Thesis, Bordeaux 1, 2008. http://www.theses.fr/2008BOR13667/document.
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L’étude précise des transitions ß de Fermi super-permises 0+ ? 0+ offre un outil précieux pour explorer les propriétés de l’interaction faible dans le cadre du Modèle Standard (SM). Collectivement, les forces (ft) mesurées pour ces transitions permettent de vérifier l’hypothèse CVC et contribuent au test le plus rigoureux de l’unitarité de la première ligne de la matrice de mélange des quarks CKM en fournissant l’évaluation la plus précise de l’élément dominant (Vud). Jusqu’à récemment, un apparent défaut d’unitarité a semé le doute sur la validité du SM minimal et a mobilisé un effort considérable afin d’élargir le champ d’étude à d’autres émetteurs de Fermi. Le 62Ga et 38Ca sont parmi des noyaux clés pour mener ces tests de précision au travers de la vérification de la fiabilité des corrections imposées aux valeurs ft expérimentales. La décroissance ß de 62Ga a été étudiée auprès du séparateur IGISOL à Jyväskylä, avec un dispositif composé de 3 Clovers EUROBALL pour la détection du rayonnement ?. La mise en évidence de raies ? de très faible intensité (<1‰), au travers de corrélations ß-? et ß-?-?, a permis de reconstruire partiellement le schéma de niveaux excités dans le 62Zn. Le rapport d’embranchement analogue déduit (B.R.A = 99.893(24) %) est utilisé pour extraire la valeur Ft(62Ga) universelle. Celle-ci s’avère en bon accord avec les 12 valeurs précises connues de la littérature. La compatibilité constatée entre la limite supérieure dressée ici sur le terme (d1IM) et la prédiction théorique confirme l’importance des corrections de brisure de symétrie d'isospin dans les émetteurs ß (A = 62). L’étude de la décroissance de 38Ca a été réalisée auprès de l’installation ISOLDE du CERN. L’utilisation de la fluoration des fragments de réaction, pour isoler chimiquement les isotopes d’intérêt, alliée au piégeage d’ions assisté par REXTRAP et l’analyse TOF, ont permis de s’affranchir totalement du contaminant contraignant 38mK. Pour la première fois, la durée de vie de 38Ca est mesurée avec un échantillon de haute pureté. Le résultat préliminaire établi T1/2(38Ca) = 445.8(10) ms améliore la précision par rapport à l’ancienne valeur d’un facteur proche de 10Precise measurements of Fermi superallowed 0+? 0+ ß decays provide a powerful tool to study the weak interaction properties in the framework of the Standard Model (SM). Collectively, the comparative half-lives (ƒt) of these transitions allow a sensitive probe of the CVC hypothesis and contribute to the most demanding test of the unitarity of the quarks-mixing CKM matrix top-row, by providing, so far, the most accurate determination of its dominant element (Vud). Until recently, an apparent departure from unity enhanced a doubt on the validity of the minimal SM and thus stimulated a considerable effort in order to extend the study to other Fermi emitters available. The 62Ga and 38Ca are among key nuclei to achieve these precision tests and verify the reliability of the corrections applied to the experimental ƒt-values. The 62Ga ß-decay was investigated at the IGISOL separator in Jyväskylä, with an experimental setup composed of 3 EUROBALL Clovers for ?-ray detection. Very weak intensity (<1‰) ?-rays were identified, via ß-? and ß-?-? correlations, and allowed a partial decay scheme reconstruction in 62Zn. The newly established analog branching-ratio (B.R.A = 99.893(24) %) was used to compute the universal Ft-value (62Ga). The latter turned out to be in good agreement with the 12 well-known cases. Compatibility between the upper limit set here on the term (d1IM) and the theoretical prediction suggests that the isospin-symmetry-breaking correction is indeed large for the heavy (A = 62) ß-emitters. The study of the 38a decay was performed at the CERN- ISOLDE facility. Injection of fluorine into the ion source, in order to chemically select the isotopes of interest, assisted by the REXTRAP Penning trap facility and a TOF analysis, enabled us to eliminate efficiently the troublesome 38mK. For the first time, the 38Ca half-life is measured with a highly purified radioactive sample. The preliminary result obtained, T1/2(38Ca) = 445.8(10) ms, improves the precision on the half-life as determined from previous measurements by a factor close to 10
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Bey, Anissa. "Test du Modèle Standard à basse énergie :- Mesure précise des rapports d'embranchement de 62Ga- Mesure précise de la durée de vie de 38Ca." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2008. http://tel.archives-ouvertes.fr/tel-00404413.
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L'étude précise des transitions β de Fermi super-permises 0+ → 0+ offre un outil précieux pour explorer les propriétés de l'interaction faible dans le cadre du Modèle Standard (SM). Collectivement, les forces (ft) mesurées pour ces transitions permettent de vérifier l'hypothèse CVC et contribuent au test le plus rigoureux de l'unitarité de la première ligne de la matrice de mélange des quarks CKM en fournissant l'évaluation la plus précise de l'élément dominant (Vud). Jusqu'à récemment, un apparent défaut d'unitarité a semé le doute sur la validité du SM minimal et a mobilisé un effort considérable afin d'élargir le champ d'étude à d'autres émetteurs de Fermi. Le 62Ga et 38Ca sont parmi des noyaux clés pour mener ces tests de précision au travers de la vérification de la fiabilité des corrections imposées aux valeurs ft expérimentales. La décroissance β de 62Ga a été étudiée auprès du séparateur IGISOL à Jyväskylä, avec un dispositif composé de 3 Clovers EUROBALL pour la détection du rayonnement γ. La mise en évidence de raies γ de très faible intensité (<1‰), au travers de corrélations β-γ et β-γ-γ, a permis de reconstruire partiellement le schéma de niveaux excités dans le 62Zn. Le rapport d'embranchement analogue déduit (B.R.A = 99.893(24) %) est utilisé pour extraire la valeur Ft(62Ga) universelle. Celle-ci s'avère en bon accord avec les 12 valeurs précises connues de la littérature. La compatibilité constatée entre la limite supérieure dressée ici sur le terme (δ1IM) et la prédiction théorique confirme l'importance des corrections de brisure de symétrie d'isospin dans les émetteurs β (A ≥ 62). L'étude de la décroissance de 38Ca a été réalisée auprès de l'installation ISOLDE du CERN. L'utilisation de la fluoration des fragments de réaction, pour isoler chimiquement les isotopes d'intérêt, alliée au piégeage d'ions assisté par REXTRAP et l'analyse TOF, ont permis de s'affranchir totalement du contaminant contraignant 38mK. Pour la première fois, la durée de vie de 38Ca est mesurée avec un échantillon de haute pureté. Le résultat préliminaire établi T1/2(38Ca) = 445.8(10) ms améliore la précision par rapport à l'ancienne valeur d'un facteur proche de 10.
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Madar, Romain. "Identification des leptons tau et recherche du boson de Higgs dans l'état final mu+tau dans l'expérience D0 auprès du Tevatron." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00620824.
Full textAbstract:
La notion de symétrie de jauge est au coeur de notre compréhension de l'interaction électrofaible et permet d'expliquer l'ensemble des observations expérimentales actuelles. Pourtant, l'incompatibilité intrinsèque entre l'invariance de jauge et la masse des particules nécessite d'introduire une nouvelle particule, le boson de Higgs, toujours non observée à ce jour. Cette thèse présente l'analyse de 7.3/fb de collisions protons-antiprotons à sqrt{s} = 1.96 TeV enregistrées par le détecteur D0 au Tevatron en vue de la recherche du boson de Higgs dans l'état final mu+tau. Cette analyse vient compléter les canaux principaux dimuons, électron-muon et diélectrons en exploitant également la désintégration H -> WW -> lvlv, majoritaire dans la fenêtre de masse accessible au Tevatron. L'état final contenant un lepton tau, leur identification parmi les jets a été améliorée d'environ 15% grâce au développement de plusieurs idées : l'ajustement des paramètres du réseau de neurones d'identification, la prise en compte de certaines dépendances cinématiques des performances de l'algorithme, l'exploitation du temps de vie du lepton tau et une étude exhaustive visant à inclure la mesure du détecteur de pieds de gerbe dans le processus d'identification. Dans un second temps, la recherche du boson de Higgs dans l'état final mu+tau étant dominée par le bruit de fond W+jets (où un jet est faussement identifié comme un lepton tau), une méthode a été élaborée pour obtenir une modélisation convenable de ce bruit de fond, non fournie par la simulation par défaut. Cette méthode est basée, entre autres, sur l'étude de la corrélation de charge entre le muon et le candidat tau qui permet de mesurer ce bruit de fond dans les données en excluant la région du signal. Ensuite, l'exploitation des cinématiques et/ou topologies différentes du signal et du bruit de fond a permis d'optimiser cette recherche atteignant alors une sensibilité attendue (observée) de 7.8 (6.6) fois le Modèle Standard pour une masse de 165 GeV/c2. Enfin, l'interprétation de l'analyse dans un scénario à quatre familles de fermions a été effectuée. Pour la première fois, cette analyse est incluse dans les combinaisons D0 et Tevatron présentées à Moriond EW et EPS 2011.
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Nicol, Michelle. "Analysis of the rare decay B->K*ee at LHCb." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112354/document.
Full textAbstract:
Grâce à la grande section efficace de production de paires bb, LHC offre une excellente occasion de faire des études de courants neutres changeant la saveur. Ces transitions sont sensibles aux effets de nouvelle physique. Cette thèse porte sur l'analyse des événements B->K*ee qui permettent de mesurer la fraction de photon avec une polarisation droite et donc de rechercher des signaux de nouvelle physique émis dans la transition b ->s. En effet, dans le Modèle Standard, la polarisation des photons est gauche. La paire e+e, lors que la masse invariante de la paire de leptons est basse, provient d'un photon virtuel et permet donc de sonder la polarisation de celui-ci. Cette mesure se fait grâce à l'étude des distribution angulaires de cette désintégration à quatre corps. Une première étape est la mesure du rapport d'embranchement dans le domaine de masse 30-1000MeV=c2. En effet, cette désintégration n'a jamais été observée dans cette région, y compris auprès des usines a B a cause du très faible rapport d'embranchement. Cette analyse comportant des électrons de basse impulsion transverse est expérimentalement complexe dans un environnement tel que celui du LHC. La mesure est faite relativement au rapport d'embranchement de la désintégration B->J/Psi(ee)K*. En effet, cela permet de s'affranchir de nombreux effets expérimentaux ainsi que de la détermination absolue des efficacités. Le résultat, repose sur les données collectées par LHCb en 2011 et correspondant a une luminosité intégrée de 1 fb-1: B(B->K*ee)30-1000MeV = (3:19+0:75-0:68(stat) +/- 0:21(syst) =/-0.15(PDG)) x10-7 en utilisant la valeur PDG pour le rapport d'embranchement de la désintégration B->J/Psi(ee)K*. La dernière partie de la thèse porte sur des études Monte Carlo qui montrent que la précision sur la fraction de photon avec une polarisation droite que l'on peut espérer obtenir avec l'inclusion des données de 2012 est d'environ 0.1, comparable à la moyenne mondiale obtenue avec des méthodes différentesThe high bb cross section produced by the LHC offers an excellent opportunity for thestudy of flavour changing neutral current B decays, where the effects of new physics can be probed. This thesis presents an analysis of the rare decay B->K*ee which can be used to measure the polarisation of the photon in the b -> s transition. When the dilepton mass is low, the ee pair comes predominantly from a virtual photon, and the polarisation can be accessed via an angular analysis. It is predicted to be predominantly left handed in the Standard Model, and therefore an enhanced right handed amplitude would be a sign of new physics. A first step is to measure the branching fraction in the dilepton mass range, 30 MeV to 1 GeV. This decay has not yet been observed in this region, due to its small branching ratio. The analysis involves electrons with low transverse momentum, and is thus experimentally complex in the hadronic environment at the LHC. The branching ratio is measured relative to that of B->J/Psi(ee)K*, which eliminates both certain experimental effects, and the need to determine absolute effciencies. The result is obtained with an integrated luminosity of 1 fb-1 of pp collisions, collected by LHCb during 2011 and is found to be:B(B->K*ee)30-1000MeV = (3:19+0:75-0:68(stat) +/- 0:21(syst) =/-0.15(PDG) x10-7 when using the PDG value for the B->J/Psi(ee)K* branching ratio. The last part of the thesis presents Monte Carlo studies, showing that with the inclusion of the 2012 data sample, the expected sensitivity on the fraction of right handed polarisation is approximately 0.1, which is comparable with the world average obtained with different methods
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Bouchart, Charles. "Phenomenology of the electroweak sector in warped (supersymmetric) extra-dimensional models." Paris 11, 2010. http://www.theses.fr/2010PA112331.
Full textAbstract:
On se place dans le cadre des modèles à dimension supplémentaire courbe adressant le problème de hiérachie de jauge. On considère ainsi le scenario suggéré par Randall et Sundrum sous l'hypothèse habituelle d'une symétrie de jauge custodiale étendue à l'espace total à 5 dimensions, permettant de protéger le modèle de trop larges corrections dans le secteur électrofaible, où le champ de Higgs est indépendament localisé sur ce qui est appelée la TeV-brane. Après avoir revu les bases de théorie des champs en dimensions supplémentaires, on introduit le cadre théorique des modèles RS, nous exposons en détail la construction de notre modèle phénoménologique, ainsi que les effets engendrés par la brisure de symétrie électrofaible sur notre modèle. Nous déterminons ensuite les diverses représentations minimales des multiplets de quarks sous la symétrie custodiale permettant de résoudre l'anomalie sur l'asymétrie avant-arrière du quark bottom. Il est ensuite montré en detail qu'il existe de fortes corrections à la valeur moyenne dans le vide du Higgs induites par de forts mélanges des bosons de jauge Z et W avec leurs exitations de KK. Le lien avec les tests de précision électrofaible est développé. Nous trouvons ainsi de substancielles corrections dûes à RS aux divers couplages au Higgs, pouvant affecter sa phénoménologie. La fin de cette thèse est dédiée aux extensions SupersSymétriques des modèles à dimension supplémenaire courbe, le champ de Higgs étant toujours confiné sur la TeV-braneLn the framework of warped extra dimension models addressing the gauge hierarchy problem, we consider the Randall-Sundrum scenario under the usual hypothesis of a bulk custodial symmetry protecting the model from large ElectroWeak corrections together with a Higgs field localized on the so-called TeV-brane. After reviewing the basics of field theory in extra dimensions, we introduce the RS framework, and show in details the construction of our phenomenological model as well as the effects of EW symmetry breaking. We determine the several minimal quark representations allowing to address the anomalies in the forward-backward b-quark asymmetry. It is then shown in details that there can exist large corrections to the Higgs boson Vacuum Expectation Value induced by mixings of the gauge bosons with their KK excitations. The connection with EW precision tests is developed. We find possibly substantial RS corrections to the various Higgs couplings able to affect its phenomenology. The end of this thesis is dedicated to SuperSymmetric extension of warped models, the Higgs field still being confined on the TeV-brane
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Li, Shu. "Mesure de la production W+W− dans les collisions proton-proton à $\sqrt{s} = 7 TeV avec le détecteur ATLAS au LHC." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4107.
Full textAbstract:
Cette thèse présente le mesure des sections efficaces de production WW MS et la détermination des couplages triples (TGCs) correspondants en utilisant ces 4.7 fb⁻¹ de donnes 2011 de collision pp. Ces mesures permettent un test contraignant du secteur 'électrofaible non abélien SU(2) X U(1) du Modèle Standard; donnent l'opportunité de sonder la nouvelle physique `a travers les couplages triples anormaux de bosons de jauge (aTGCs) qui seront observés dans la distribution des variables cinématiques des WW produits ou de leurs produits de désintégration finaux dans le secteur de haute 'énergie; et permettent d'avoir une bonne compréhension du bruit de fond irréductible dans la recherche du boson de Higgs dans le canal de d'esint'egration H → W⁺W⁻.Ce travail de th`ese donne un base solide pour les mesures à venir de la production WW avec les ∼25 fb⁻¹ de luminosité intègré de donnes a 8 TeV prévue pour la fin 2012, qui conduiront vers une amélioration de la précision et des limites plus strictes sur les aTGCsThis thesis presents a measurement of the SM WW production cross section and the determination of the corresponding limits on anomalous triple gauge boson couplings (aTGCs), using the 2011 4.7 fb⁻¹ pp collisions data at 7 TeV collected in 2011. The measurement allows for a stringent test of the non-Abelian SU(2) X U(1) SM electroweak sector and probes new physics that could manifest itself through aTGCs that may alter the observed production cross section or kinematic distributions. This measurement also provides a good understanding of the irreducible background in searches for the Higgs boson through the H → W⁺W⁻ decay channel.This thesis work has laid a solid foundation for further measurements of the WW production with the ∼25 fb⁻¹ integrated luminosity 8 TeV recorded data expected by the end of 2012, which will further improve the precision and yield more stringent limits on the aTGCs
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Faïf, Anne-Marie Garance. "Mesure de la section efficace totalement leptonique et des rapports d'embranchement des bosons W+- dans le cadre de l'expérience ALEPH à LEP2." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10248.
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Ce travail de these s'inscrit dans le cadre des mesures de precision effectuees a lep2. Les bosons w# y sont produits par paires dans les collisions e#+e#. Les etats finals totalement leptoniques (l$$$$l) representent 10. 5% de ces desintegrations. Ce canal s'ajoute aux canaux hadroniques et semi-leptoniques pour contraindre le modele standard. Les etats finals l$$$$l, caracterises par deux leptons charges energiques et acolineaires ainsi qu'une importante impulsion transverse manquante, ont ete selectionnes parmi les donnees enregistrees par l'experience aleph entre 1996 et 1998. Les sections efficaces totalement leptoniques correspondantes ont ete calculees afin de determiner les rapports d'embranchement du boson w. Contrairement aux mesures effectuees au tevatron, les rapports d'embranchement sont determines sans contrainte theorique. La precision obtenue au lep sur les rapports d'embranchement leptoniques individuels et le rapport d'embranchement hadronique du w est la meilleure a ce jour. Les resultats obtenus ne montrent pas de deviation significative par rapport aux predictions du modele standard.
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Fromme, Lars [Verfasser]. "Electroweak baryogenesis in extensions of the standard model / presented by Lars Fromme." 2006. http://d-nb.info/980804515/34.
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Olszewski, Paweł. "Electroweak Vacuum in Standard Model and in its Extension Motivated by Scale Symmetry." Doctoral thesis, 2019. https://depotuw.ceon.pl/handle/item/3506.
Full textAbstract:
At the beginning of the thesis the following aspects of quantum field theory are
presented: momentum and loop expansion of scalar effective action, spontaneous
breaking of a symmetry and vacuum instability. They are discussed in detail both in
general and in the context of particular gauge-symmetric models including the Stan-
dard Model. Then scale symmetry is introduced with emphasis on its interplay with
renormalization of the model. The notion of quantum scale symmetry is defined and
used to propose a novel extension of the Standard Model. Stability of the electroweak
vacuum is compared between the extension and the Standard Model.Teza na początku omawia następujące zagadnienia kwantowej teorii pola: pędowe i pętlowe rozwinięcie perturbacyjne skalarnego działania efektywnego, spontaniczne łamanie symetrii i niestabilność próżni. Są one szczegółowo dyskutowane zarówno w ogólnym kontekście, jak i na konkretnych przykładach teorii z cechowaniem, w tym Modelu Standardowego. Następnie do rozważań wprowadzona zostaje symetria skalowania, ze szczególnym uwzględnieniem problemu renormalizacji modelu. Po- jęcie kwantowej symetrii skalowania zostaje zdefiniowane i użyte do zaproponowa- nia nowego rozszerzenia Modelu Standardowego. Stabilność próżni elektrosłabej jest porównana między przedstawionym rozszerzeniem a Modelem Standardowym.
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Long, Brian Alexander. "WWW production at the LHC." Thesis, 2016. https://hdl.handle.net/2144/17737.
Full textAbstract:
In 2012 a resonance with a mass of 125 GeV resembling the elusive Higgs boson was discovered simultaneously by the ATLAS and CMS experiments using data collected from the Large Hadron Collider (LHC) at CERN. Its observation finally confirms the mechanism for Spontaneous Electroweak Symmetry Breaking (EWSB) necessary for describing the mass structure of the electroweak (EW) gauge bosons. In 2013, Peter Higgs and Francois Englert were awarded the Nobel Prize in physics for their work in developing this theory of EWSB now referred to as the Higgs mechanism. The explanation for EWSB is often referred to as the last piece of the puzzle required to build a consistent theory of particle physics known as the Standard Model. But does that mean that there are no new surprises to be found? Many EW processes have yet to be measured and are just starting to become accessible with the data collected at the LHC. Indeed, this unexplored region of EW physics may provide clues to as yet unknown new physics processes at higher energy scales. Using the 2012 LHC data recorded by the ATLAS experiment, we seek to make the first observation of one such EW process, the massive tri-boson final state: WWW. It represents one of the first searches to probe the Standard Model WWWW coupling directly at a collider. This search looks specifically at the channel where each W boson decays to a charged lepton and a neutrino, offering the best sensitivity for making such a measurement. In addition to testing the Standard Model directly, we also use an effective field theory approach to test for the existence of anomalous quartic gauge couplings which could offer evidence for new physics at higher energies than those produced by the LHC.
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Lee, Christopher. "Probing Physics and the Standard Model and Beyond with Electroweak Baryogenesis and Effective Theories of the Strong Interactions." Thesis, 2005. https://thesis.library.caltech.edu/2160/1/thesis.pdf.
Full textAbstract:
We address in this thesis two primary questions aimed at improving our ability to calculate reliably in the Standard Model of particle physics and probing possible new particles which may exist beyond it.
First, we embark on an attempt to account for the abundance of matter in the present Universe if earlier in its history matter and antimatter were equally abundant. We explore whether baryogenesis at the electroweak phase transition could successfully account for the observed density of baryons in the Universe, using the closed-time-path (CTP) formalism of quantum field theory to calculate the buildup and relaxation of particle densities during the phase transition. For our model of the new particles and sources of CP violation necessary to account for the baryon asymmetry of the Universe, we adopt the Minimal Supersymmetric Extension of the Standard Model (MSSM). We look for regions of the parameter space in the MSSM that could give rise to sufficiently large baryon asymmetry without violating constraints on these parameters from existing experiments, in particular, constraints on masses of Higgs and supersymmetric particles from accelerator searches and precision electroweak tests, and on CP-violating parameters of the MSSM from searches for electric dipole moments of elementary particles.
Next, we explore how to get around our ignorance of the dynamics of strongly interacting particles in the nonperturbative regime of Quantum Chromodynamics (QCD) by the clever use of effective field theories. Two applications are explored: the decay of Z bosons to hadronic jets using soft-collinear effective theory (SCET) and the radiative decays of quarkonia to light hadrons using SCET and non-relativistic QCD (NRQCD). These tools facilitate the proof of factorization of decay rates into perturbatively-calculable and nonperturbative parts. Universality of the latter among different observables provides predictive power even in our ignorance of the details of the nonperturbative physics.
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Konstandin, Thomas [Verfasser]. "CP-violation and baryogenesis on electroweak scales : cosmological predictions for the standard model and beyond / presented by Thomas Konstandin." 2005. http://d-nb.info/975800280/34.
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Li, Yen-Ting, and 李彥頲. "Standard Model with a Real Singlet Scalar: An Investigation of Scheme Dependence and Gauge Dependence in Electroweak Phase Transition." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/bb7e33.
Full textAbstract:
碩士國立臺灣大學
物理學研究所
107
In this thesis, the standard model is extended with a real singlet scalar $S$ to achieve a two-step electroweak phase transition (EWPT). The model is investigated with several schemes to quantify the scheme dependence and the gauge dependence issue. In on-shell(OS)-like scheme, at the one-loop order, Nambu-Goldstone boson contributions are needed to be resummed to circumvent the IR divergence; their effects in the EWPT are studied and quantified. The critical temperatures and critical vacuum expectation values of the EWPT in the OS-like and the MS-bar schemes are highly consistent to each other; we also compare the results with two gauge-independent schemes (the high temperature and the Patel-Ramsey-Musolf schemes). Even though higher order corrections are needed for scale-dependent schemes, the general trend of the results are consistent and the analyses show the differences of gauge-dependent and -independent schemes are within theoretical uncertainties.
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GORI, VALENTINA. "Search for a high mass Higgs-like boson produced via Vector Boson Fusion, in the decay channel H -> ZZ -> llqq (l=e, mu) with the CMS detector." Doctoral thesis, 2015. http://hdl.handle.net/2158/1020428.
Full textAbstract:
Nella tesi si presenta il lavoro di analisi condotto nell'ambito dell'esperimento CMS ad LHC per la ricerca di un bosone di Higgs ad alta massa, prodotto con il meccanismo della Vector Boson Fusion e con decadimento in due bosoni Z, che a loro volta decadono in una coppia di leptoni e una coppia di quark. I risultati sono interpretati sia nell'ambito del Modello Standard che nello scenario di Electroweak singlet. Si sono usate tecniche multivariate (machine learning).
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Gumpert, Christian. "Measurement of Electroweak Gauge Boson Scattering in the Channel pp → W ± W ± jj with the ATLAS Detector at the Large Hadron Collider." Doctoral thesis, 2014. https://tud.qucosa.de/id/qucosa%3A28577.
Full textAbstract:
Particle physics deals with the elementary constituents of our universe and their interactions. The electroweak symmetry breaking mechanism in the Standard Model of Particle Physics is of paramount importance and it plays a central role in the physics programmes of current high-energy physics experiments at the Large Hadron Collider. The study of scattering processes of massive electroweak gauge bosons provides an approach complementary to the precise measurement of the properties of the recently discovered Higgs boson. Owing to the unprecedented energies achieved in proton-proton collisions at the Large Hadron Collider and the large amount of data collected, experimental studies of these processes become feasible for the first time. Especially the scattering of two W± bosons of identical electric charge is considered a promising process for an initial study due to its distinct experimental signature. In the course of this work, 20.3 fb−1 of proton-proton collision data recorded by the ATLAS detector at a centre-of-mass energy of √s = 8 TeV are analysed. An analysis of the production of two W± bosons of identical electric charge in association with two jets, pp → W ± W ± jj, is conducted in the leptonic decay channel of the W± bosons.
Thereby, emphasis is put on the development of methods for the estimation of experimental backgrounds as well as on the optimisation of the event selection. As a result of this work, first experimental evidence for the existence of the aforementioned process is established with an observed significance of 4.9. Based on the number of observed events in the selected phase space the extracted fiducial cross section is σ(fid) = (2.3 ± 0.5(stat.) +0.4/−0.3 (sys.)) fb which is in agreement with the prediction of the Standard Model of σ(fid,SM) = (1.6 ± 0.2) fb. Of particular theoretical interest are electroweak contributions to the pp → W ± W ± jj process due to their sensitivity to the nature of the electroweak symmetry breaking mechanism. Criteria for a dedicated event selection are investigated and implemented in the analysis with the goal of enhancing the sensitivity to these contributions. First experimental evidence for the presence of electroweak contributions to the pp → W ± W ± jj process can be claimed with an observed significance of 4.1. The cross section extracted in the selected phase space region is found to be σ(fid) = (1.7 +0.5/−0.4 (stat.) ± 0.3(sys.)) fb which is 1.3 standard deviations above the theoretical prediction of the Standard Model of σ(fid,SM) = (1.0 ± 0.1) fb.
A variety of extensions to the Standard Model predict modifications to the electroweak gauge sector. In the context of the electroweak chiral Lagrangian, which serves as an effective approximation of these theories in the energy regime E = 1 − 3 TeV, anomalous contributions to the quartic WWWW gauge coupling can be described by the parameters α4 and α5 . The selection of events is optimised again to enhance the sensitivity to these two parameters. On the basis of the number of events observed in this phase space region, the following one-dimensional confidence intervals at the 95% confidence level are derived: −0.09 ≤ α4 ≤ 0.10 and −0.15 ≤ α5 ≤ 0.15. At present, these limits represent the most stringent constraints on contributions from new physics processes to the quartic WWWW gauge coupling.
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GONZI, SANDRO. "Study of gamma + jets data with the CMS detector in pp collisions at sqrt(s) = 8 TeV." Doctoral thesis, 2014. http://hdl.handle.net/2158/839694.
Full textAbstract:
The characterization of the production process of prompt photons γ in association with hadronic jets (γ + jets process) at the Large Hadron Collider (LHC), is one of the goals in physics analyses at the Compact Muon Solenoid (CMS) experiment.
This channel provides a way of directly probing the hard scattering process and it is directly sensitive to the gluonic content of the proton. This process is also the starting point for the study of many Standard Model signatures, and constitutes a background for important searches, such as H->γγ, or SUSY and extra-dimensions with energetic photons in the final state.
This thesis presents the measurement of the γ + jets differential cross section production as a function of the photon transverse momentum pT in the high pT kinematic region, in proton-proton collisions at a center-of-mass energy of sqrt(s) = 8 TeV collected by the CMS detector with an integrated luminosity equal to L = (19.7 ± 0.5) fb(-1).
A series of selection cuts have been applied in order to identify the γ + jets process with respect to the background.
The selection efficiencies have been extracted with a data-driven method (Tag & Probe) and have been used to correct the efficiencies extracted from the Monte Carlo simulations.
To perform a precise set of measurements in the γ + jets final state, a background extraction with a data-driven approach has been applied by using a data-driven modeling for signal and background.
The calculation of the differential cross section has then been performed after a bin-by-bin correction of the detector effects on the selected photons.
A detailed treatment of the systematic uncertainties affecting the process has also been performed.
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Pan, Jie. "Towards a Precision Measurement of Parity-Violating e-p Elastic Scattering at Low Momentum Transfer." 2012. http://hdl.handle.net/1993/8124.
Full textAbstract:
The goal of the Q-weak experiment is to make a measurement of the proton's weak charge ($Q^p_W = 1-4\sin^2\theta_W$) to an accuracy of ~4%. This would represent a ~0.3% determination of the weak mixing angle ($\sin^2\theta_W$) at low energy. The measurement may be used for a precision test of the Standard Model (SM) prediction on the running of $\sin^2\theta_W$ with energy scale. The Q-weak experiment operates at Thomas Jefferson National Accelerator Facility (Jefferson Lab). The experiment determines the proton's weak charge by measuring the parity violating asymmetry in elastic electron-proton scattering at low momentum transfer $Q^2 = 0.026 (GeV/c)^2$ and forward angles (~8 degree). The anticipated size of the asymmetry, based on the SM, is about 230 parts per billion (ppb). With the proposed accuracy, the experiment may probe new physics beyond Standard Model at the TeV scale. This thesis focuses on my contributions to the experiment, including track reconstruction for momentum transfer determination of the scattering process, and the focal plane scanner, a detector I designed and built to measure the flux profile of scattered electrons on the focal plane of the Q-weak spectrometer to assist in the extrapolation of low beam current tracking results to high beam current. Preliminary results from the commissioning and the first run period of the Q-weak experiment are reported and discussed.
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Soukup, Petr. "Elektroslabé procesy v rámci efektivní polní teorie." Master's thesis, 2009. http://www.nusl.cz/ntk/nusl-275933.
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Title: Electroweak processes in the framework of effective field theory Author: Petr Soukup Department: Institute of Particle and Nuclear Physics Supervisor: RNDr. Karol Kampf, Ph.D. Supervisor's e-mail address: kampf@troja.mff.cuni.cz Abstract: In this thesis, we study electroweak processes within the framework of ef- fective field theory employing the approach of effective Lagrangians. We mainly focus on the decay process H → γγ. A complete set of SU(2) × U(1) invariant dimension- six operators is utilized. We present a brief introduction to GWS Standard model and dimension-six effective operators. One-loop Standard model contribution to the process of H → γγ is then evaluated, followed by calculation of tree-level and one-loop level dimension-six operators contribution to the same process. We then present a brief ge- neral summary of renormalization procedure in quantum field theory. Renormalization of performed calculations is implemented, and possible issues that may arise during renormalization of such non-renormalizable theory are also discussed. In the end, we discuss the obtained results, mainly the dependence of H → γγ decay rate on effective theory's free parameters and the scale of the new physics Λ. Focus is made on possible deviations from Standard model results. The results are plotted in charts....