<p>The Standard Model describes all elementary particles known today, but at larger energies it will have to be complemented with new particles and interactions. To be able to distinguish new physics at proton colliders such as LHC at CERN, it is essential to have an appropriate description of the colliding protons and their interactions. The study of the proton is important also in itself, to get a better understanding of the non-perturbative aspects of the strong interaction.</p><p>In paper I-IV of this thesis, a model for the non-perturbative dynamics of quarks and gluons is developed, based on quantum fluctuations in hadrons. The parton distributions of the proton are given by momentum fluctuations, with sea quark distributions generated by fluctuations into baryon-meson pairs. This model can reproduce proton structure function data, as well as measured asymmetries between up and down valence quark distributions and between the anti-up and anti-down sea. It provides an intrinsic charm quark component as indicated by data. It also predicts an asymmetry in the strange sea of the proton, which can explain the NuTeV anomaly first attributed to new physics beyond the Standard Model.</p><p>Charged Higgs bosons are predicted by several theories for new physics, including Supersymmetry. At proton colliders, the predicted dominant production mechanism is in association with top and bottom quarks. In paper V-VII, different contributions to this production are studied, and an algorithm is developed for combining the two dominant processes gb -> tH^+/- and gg -> tbH^+/-. The algorithm gives a smooth transition from small to large transverse momenta of the b-quark, which is important when the b-quark is observed. It also gives arguments for the choice of factorisation scale in the process.</p>

<p>This thesis treats two different projects, both aiming at experimental tests at hadron colliders of some specific predictions of the Standard Model (SM) of particle physics and of its Minimal Supersymmetric extension (MSSM). The thesis is based on four papers.</p><p>Papers I-III study the discovery potential for a heavy charged Higgs boson of the ATLAS experiment at the Large Hadron Collider (LHC). Charged Higgs bosons are part of the Higgs sector in many extensions to the SM and their detection would be an unambiguous sign of new physics.</p><p>If the charged Higgs boson is heavier than the top quark, its dominant decay mode is into a top and a bottom quark. Searches in this decay channel at ATLAS are difficult mainly due to the large top-quark pair-production background. The possible gain obtained when requiring 4 b-tagged jets for the signal events is studied, but no significant improvement compared to an analysis requiring 3 b-tagged jets is found.</p><p>If the masses of supersymmetric particles are sufficiently small, heavy charged Higgs bosons can decay into a chargino-neutralino pair. We show that in this decay channel charged Higgs bosons can be detected, given a favourable choice of parameters governing the MSSM.</p><p>In a large-mass-splitting MSSM scenario, the charged Higgs decay into a W boson and a neutral Higgs can have a large branching fraction. We conclude, however, that charged Higgs searches in this decay channel are made difficult by a large, irreducible SM background.</p><p>Paper IV describes a measurement of the top-quark pair production cross-section performed with the DØ detector at the Tevatron collider. Signal events in the muon+jets decay channel are selected using topological event characteristics and a preliminary result of σ(ttbar)=3.8 +1.1-1.1(stat) +0.9-0.8(syst) +0.3-0.2(lumi) pb is obtained using an integrated luminosity of 363/pb.</p>

The Standard Model describes all elementary particles known today, but at larger energies it will have to be complemented with new particles and interactions. To be able to distinguish new physics at proton colliders such as LHC at CERN, it is essential to have an appropriate description of the colliding protons and their interactions. The study of the proton is important also in itself, to get a better understanding of the non-perturbative aspects of the strong interaction. In paper I-IV of this thesis, a model for the non-perturbative dynamics of quarks and gluons is developed, based on quantum fluctuations in hadrons. The parton distributions of the proton are given by momentum fluctuations, with sea quark distributions generated by fluctuations into baryon-meson pairs. This model can reproduce proton structure function data, as well as measured asymmetries between up and down valence quark distributions and between the anti-up and anti-down sea. It provides an intrinsic charm quark component as indicated by data. It also predicts an asymmetry in the strange sea of the proton, which can explain the NuTeV anomaly first attributed to new physics beyond the Standard Model. Charged Higgs bosons are predicted by several theories for new physics, including Supersymmetry. At proton colliders, the predicted dominant production mechanism is in association with top and bottom quarks. In paper V-VII, different contributions to this production are studied, and an algorithm is developed for combining the two dominant processes gb -&gt; tH+/- and gg -&gt; tbH+/-. The algorithm gives a smooth transition from small to large transverse momenta of the b-quark, which is important when the b-quark is observed. It also gives arguments for the choice of factorisation scale in the process.

This thesis treats two different projects, both aiming at experimental tests at hadron colliders of some specific predictions of the Standard Model (SM) of particle physics and of its Minimal Supersymmetric extension (MSSM). The thesis is based on four papers. Papers I-III study the discovery potential for a heavy charged Higgs boson of the ATLAS experiment at the Large Hadron Collider (LHC). Charged Higgs bosons are part of the Higgs sector in many extensions to the SM and their detection would be an unambiguous sign of new physics. If the charged Higgs boson is heavier than the top quark, its dominant decay mode is into a top and a bottom quark. Searches in this decay channel at ATLAS are difficult mainly due to the large top-quark pair-production background. The possible gain obtained when requiring 4 b-tagged jets for the signal events is studied, but no significant improvement compared to an analysis requiring 3 b-tagged jets is found. If the masses of supersymmetric particles are sufficiently small, heavy charged Higgs bosons can decay into a chargino-neutralino pair. We show that in this decay channel charged Higgs bosons can be detected, given a favourable choice of parameters governing the MSSM. In a large-mass-splitting MSSM scenario, the charged Higgs decay into a W boson and a neutral Higgs can have a large branching fraction. We conclude, however, that charged Higgs searches in this decay channel are made difficult by a large, irreducible SM background. Paper IV describes a measurement of the top-quark pair production cross-section performed with the DØ detector at the Tevatron collider. Signal events in the muon+jets decay channel are selected using topological event characteristics and a preliminary result of σ(ttbar)=3.8 +1.1-1.1(stat) +0.9-0.8(syst) +0.3-0.2(lumi) pb is obtained using an integrated luminosity of 363/pb.

Cette thèse décrit quelques développements dans les techniques de calcul des amplitudes de diffusion en théorie supersymétrique de champ de jauge . L'accent est mis sur les relations de récurrence on-shell et sur l'utilisation de méthodes d'unitarité pour des calculs de boucle. En particulier, la récurrence on-shell est liée aux règles BCFW pour calculer les amplitudes de jauge au niveau des arbres. Les combinaisons de techniques de coupe d'unitarité et la récurrence sont utilisées pour calculer les amplitudes de boucle, et finalement, à partir des amplitudes, pour obtenir la fonction de corrélation énergie-énergie en théorie de super-Yang-Mills N = 4 à l'aide de la représentation de Mellin-Barnes. Dans le dernier chapitre, nous tentons de trouver un contour convergent pour les intégrales de Mellin Barnes en multi-dimension obtenu par une certaine approximation d'un contour de phase stationnaire.

Studies of minimum bias events at colliders probe the behavior of QCD in the non-perturbative regime. The phenomenology of events in this regime is described by empirical models that take many parameters, which all need to be tuned to the observed data. Measurements based on angular correlations between the highest transverse momentum charged particle track and the other charged particle tracks in collision events can, because of their robustness against experimental and detector effects, be a component of the tuning inputs for the models. We measure such observables in a variety of pseudorapidity ranges and at many center-of-mass energies at DØ and ATLAS. We observe that such observables are poorly described by current models and tunes that are used to produce simulated event samples, making them valuable information for the tuning process. The Matrix Element method is a powerful analysis tool to extract precise measurements from data samples of limited statistics. We have investigated the potential of the Matrix Element method to measure the mass of the charged Higgs in the exclusive decay H±→τ±ν→e±+3ν when produced in top quark decays at the Tevatron, with emphasis on the construction of transfer functions in the τ decay chain. We concluded that the τ decay chain can be successfully parametrized via a transfer function and that the method has the potential to provide an accurate charged Higgs mass measurement in this channel. Triggering on τ leptons is a key component for many beyond the Standard Model searches at ATLAS, such as the search for the charged Higgs boson. Events containing Z bosons can be used to measure the efficiency of the ATLAS τ hadronic-decay trigger. We have used a tag-and-probe method on simulated Z boson decays to 2 τ leptons where one decays to a μ while the other decays hadronically. The μ is used as the tag and the τ side is probed. We demonstrated that the efficiency of the τ hadronic-decay trigger can be accurately measured with this method using the first 100 pb-1 of ATLAS data. / Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 732

<p>The dissertation brings together approaches across the fields of physics, critical theory, literary studies, philosophy of physics, sociology of science, and history of science to synthesize a hybrid approach for instigating more rigorous and intense cross-disciplinary interrogations between the sciences and the humanities. I explore the concept of speculation in particle physics and science fiction to examine emergent critical approaches for working in the two areas of literature and physics (the latter through critical science studies), but with the expectation of contributing new insights to media theory, critical code studies, and also the science studies of science fiction. </p><p>There are two levels of conversations going on in the dissertation; at the first level, the discussion is centered on a critical historiography and philosophical implications of the discovery Higgs boson in relation to its position at the intersection of old (current) and the potential for new possibilities in quantum physics; I then position my findings on the Higgs boson in connection to the double-slit experiment that represents foundational inquiries into quantum physics, to demonstrate the bridge between fundamental physics and high energy particle physics. The conceptualization of the variants of the double-slit experiment informs the aforementioned critical comparisons. At the second level of the conversation, theories are produced from a close study of the physics objects as speculative engine for new knowledge generation that are then reconceptualized and re-articulated for extrapolation into the speculative ontology of hard science fiction, particularly the hard science fiction written with the double intent of speaking to the science while producing imaginative and socially conscious science through the literary affordances of science fiction. The works of science fiction examined here demonstrate the tension between the internal values of physics in the practice of theory and experiment and questions on ethics, culture, and morality.</p><p>Nevertheless, the dissertation hopes to show the beginnings of a possibility, through the contentious but generative space provided by speculative physics, to produce more cross-collaborative thinking between physics as represented by the hard sciences, and science fiction representing the objects of literary enterprise and creative evolution.</p> / Dissertation

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

Submitted by CAIQUE MEIRA RONQUI null (cmeiraronqui@gmail.com) on 2018-04-05T02:12:52Z No. of bitstreams: 1 mestrado.pdf: 19390845 bytes, checksum: a1c62d106479845bd9047a91fbad6b1f (MD5) / Approved for entry into archive by Hellen Sayuri Sato null (hellen@ift.unesp.br) on 2018-04-05T16:59:15Z (GMT) No. of bitstreams: 1 ronqui_cm_me_ift.pdf: 19390845 bytes, checksum: a1c62d106479845bd9047a91fbad6b1f (MD5) / Made available in DSpace on 2018-04-05T16:59:15Z (GMT). No. of bitstreams: 1 ronqui_cm_me_ift.pdf: 19390845 bytes, checksum: a1c62d106479845bd9047a91fbad6b1f (MD5) Previous issue date: 2018-02-05 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Elaboramos uma revisão de como o problema da hierarquia aparece na teoria Eletrofraca, pois entendemos que esse assunto ganhou importância e merece atenção especial. Apesar disso, notamos que muitos conceitos necessários para compreender a origem do problema encontram-se espalhados em diferentes livros e artigos, dificultando o acesso à informação. Por isso, apresentamos neste trabalho esses principais conceitos de maneira consolidada. / We develop a review on how the hierarchy problem appears in the Electroweak theory. Nowadays we think that this problem is greater in importance than it was in the past, so it deserves special attention, but we noticed several concepts needed to understand the problem are scattered in different books and papers, which hinders full access to information. Therefore, we intend to present the key subjects in a single document, because we didn't find similar work in previous studies. / 2015/19572-0

Malgré les nombreux succès du Modèle Standard de la physique des particules, plusieurs éléments montrent qu'il ne s'agit que d'une théorie effective à basse énergie. En effet, la masse des neutrinos et la matière noire ne sont pas expliqués dans ce modèle, qui ne prend pas en compte non plus la gravitation dont la version quantique n'a toujours pas été établie. De plus, les divergences quadratiques des corrections à la masse du boson de Higgs dans ce modèle pose un problème de naturalité. Tous ces problèmes indiquent la nécessité de trouver une nouvelle physique, qui doit être décrite par une extension du Modèle Standard. Une des possibilités est d'ajouter une nouvelle symétrie de l'espace-temps, la Supersymétrie, reliant les bosons et le fermions. Dans son extension miminale, la Supersymétrie permet déjà de résoudre le problème de la matière noire en proposant un candidat naturel, le neutralino, et de supprimer les dangereuses corrections quadratiques à la masse du boson de Higgs.Dans cette thèse, les travaux se sont concentrés sur une extension supersymétrique non minimale du Modèle Standard, le NMSSM. Afin de confronter la théorie aux expériences, il est nécessaire de calculer précisément les différentes observables. Ces calculs étant complexes, il est naturel de les automatiser, ce qui a été réalisé à l'aide du code SloopS. Avec ce code, nous avons pu dans un premier temps nous intéresser à la désintégration du boson de Higgs en un photon et un boson Z. Ce mode de désintégration a la particularité d'être généré directement à une boucle, ce qui le rend sensible à la présence de nouvelles particules. Il a commencé à être mesuré lors du Run 1 du LHC et les données vont continuer à s'accumuler avec le Run actuel (Run 2). La possibilité d'une déviation du signal mesuré avec celui prédit par le modèle Standard, requiert donc une analyse théorique préliminaire, que nous avons effectué dans le cadre du NMSSM. Nous nous sommes ensuite intéressé aux corrections radiatives pour des processus plus généraux.Il a d'abord fallu réaliser et implémenter la renormalisation dans SloopS afin de réguler les divergences apparaissant dans ces calculs à une boucle. Puis nous avons pu utiliser le modèle renormalisé pour calculer les corrections radiatives aux masses et largeurs de désintégration des différentes particules supersymétriques et des bosons de Higgs, en comparant les résultats obtenus dans différents schémas de renormalisation. / Although the Standard Model has been very successful so far, it presents several limitations showing that it is only an effective low energy theory. For example, the neutrino masses or dark matter are not predicted in this model. Gravity is also not taken into account and we expect that it plays a quantum role at energies around the Planck mass. Moreover, radiative corrections to the Higgs boson mass suffer from quadratic divergences. All these problems underline the fact that new physics should appear, and this has to be described by an extension of the Standard Model. One well-motivated possibility is to add a new space-time symetry, called Supersymmetry, which link bosons and fermions. In its minimal extension, Supersymmetry can already solve the dark matter paradox with a natural candidate, the neutralino, and provide a cancellation of the dangerous quadratic corrections to the Higgs boson mass.In this thesis, we focussed on the Next-to-Minimal SuperSymmetric extension of the Standard Model, the NMSSM. To compare theoretical predictions with experiments, physical observables must be computed precisely. Since these calculations are long and complex, automatisation is desirable. This was done by developping SloopS, a program to compute one-loop decay width and cross-section at one-loop order in Supersymmetry. With this code, we first analysed the decay of the Higgs boson in a photon and a Z boson. This decay mode is induced at the quantum level and thus is an interesting probe of new physics. Its measurement has been started during Run 1 of the LHC and is continued now in Run 2. The possibility of deviation between the measured signal strength and the one predicted by the Standard Model motivates a careful theoretical analysis in beyond Standard Models which we realised within the NMSSM. Our goal was to compute radiative corrections for any process in this model. To cancel the ultraviolet divergences appearing in higher order computations, we had to carry out and implement the renormalisation of the NMSSM in SloopS. Finally, it was possible to use the renormalised model to compute radiatives corrections to masses and decay widths of Higgs bosons and supersymmetric particles in the NMSSM and to compare the results between different renormalisation schemes.