Dissertationen zum Thema „Boston Association“
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1
Watkin, Thomas. „Les sociétés de développement communautaire à Boston : ethnographie d’un territoire professionnel en construction“. Paris, EHESS, 2014. http://www.theses.fr/2014EHES0069.
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En prenant le cas des sociétés de développement communautaire (CDCs) dans la ville de Boston aux Etats-Unis, cette thèse interroge la construction d'un territoire professionnel structuré dans l'espace social et physique qu'est la community. Ces organisations inscrites dans des quartiers populaires incarnent l'évolution des pratiques du développement communautaire et la professionnalisation d'un mouvement associatif engagé dans le domaine du logement et dans de multiples activités économiques et sociales. Pour cela, cette thèse entend identifier cet espace qu'est la community comme un réseau d'acteurs et un ensemble de pratiques spatialisées. Après en avoir saisi son institutionnalisation par l'Etat et un ensemble d'acteurs, la thèse propose d'étudier la structure organisationnelle de la CDC comme la résultante d'une action dans le domaine immobilier et d'un mouvement social. Examinée à partir de son émergence durant les années soixante jusqu'à la crise économique et financière de 2007-2011 cette analyse se base sur des méthodes d'analyse de réseaux sociaux et une exploration ethnographique des identités professionnelles façonnées par l'engagement individuel dans l'espace de la community. Des situations d'affirmation collective d'existence des CDCs illustrent cette extension territoriale des pratiques et les tensions qu'elle exerce sur les acteurs qui y prennent part. Enfin, l'identification de ce territoire professionnel est observée à travers l'expérience de la crise économique et des crédits immobiliers au cours de laquelle la community devient à la fois un espace propice au changement et un espace d'adaptation face à une situation instableTaking the case of community development corporations (CDCs) in the city of Boston in the United States, this dissertation questions the construction of a structured professional territory in the social and physical space of the community. These CDCs operating in poor neighborhoods embody the evolution of the community development field and the professionalization of committed organizations in the field of housing and in multiple economy and social activities. In this context, this thesis aims to identify the community space as a network of actors and a set of spatial practices. After explaining its institutionalization by the state and a group of actors, this dissertation proposes to study the organizational structure of the CDCs as the result of a combination of real estate activities and a social movement. Examined from its emergence during the sixties to the economy and financial crisis of 2007-2011, this analysis is based on the methods of social network analysis and an ethnographic exploration of professional identifies shaped by the commitment and movement of individuals in the space of the community. Situations of collective affirmation of the existence of CDCs illustrate this territorial extension of the practices and the tensions it has on the players who take part of it. Finally, the identification of this professional territory is viewed through the experience of the economic crisis and housing mortgages generating relationships between actors and in which the community becomes both a space for change and adaptation to face an unstable situation
2
Xu, Chao. „Mesure du rapport des sections efficaces des bosons W et Z produits en association avec un jet dans les collisions proton-proton a √ s=7 TeV avec le detcteur ATLAS“. Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112091.
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Dans cette thèse la mesure du rapport des sections efficaces de production de bosons W et Z en association avec un jet au LHC est effectuée.Le rapport des sections efficaces est mesuré à l'aide des données issues de collisions proton-proton au LHC à une énergie dans le centre de masse de 7 TeV, recueillies par l'expérience ATLAS en 2010, correspondant à une luminosité intégrée d'environ 40 pb-1. L'analyse est effectuée à l’aide de bosons W et Z se désintégrant dans le canal muon.Il s'agit de la première mesure du rapport des taux de production de bosons W et Z associés à un jet réalisée à une si haute énergie dans le centre de masse, la mesure est la également la première effectuée au LHC. Cette mesure constitue un test très important des calculs théoriques perturbatifs et tire avantage des annulations partielles ou totales de diverses incertitudes expérimentales.La mesure sert aussi pour les recherches de nouveaux phénomènes de physique au LHC à contraindre les bruits de fonds ayant les mêmes signatures topologiques.La valeur du rapport de mesuré est présentée en fonction de différents seuils d’impulsion transverse de jet cumulatifs et est trouvé, a l’intérieur de la précision statistique, en bon accord avec prédictions pertubatives de QCD aux LO et NLOIn this thesis an investigation of the ratio of the production cross section of W and Z bosons in association with one jet at LHC is performed.The cross-section ratio is measured with LHC proton-proton collision data at a center-of-mass energy of 7 TeV, collected by the ATLAS experiment in 2010, corresponding to an integrated luminosity of approximately 40 pb-1. The analysis is performed selecting W and Z bosons decaying in the muon channel.It is the first time the ratio of W and Z bosons production associated with one jet is measured at such a high center-of-mass energy, the measurement is the first one at the LHC. This measurement constitutes a very important test of perturbative theoretical calculations based on the advantage of the partial and full cancellations of various uncertainties.It also serves as constraining backgrounds with similar topological signatures in the search for new physics phenomena at the LHC. The measured ratio value is presented as a function of cumulative jet transverse momentum thresholds and found, within statistical precision, to agree well with perturbative LO and NLO QCD predictions
3
Dumitriu, Ana Elena. „Study of the Higgs production in association with tt quarks“. Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0295/document.
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Le travail scientifique présenté dans cette thèse s’appuie sur des collisions proton proton, à 13 TeV dans le centre de masse, produite par le grand collisionneur de Hadron (LHC) et enregistrées entre 2015 et 2017 par le détecteur ATLAS. Après une brève introduction sur le programme de physique du LHC, le premier chapitre donne un aperçu complet du contexte et des motivations théorique. Ensuite une description complète du détecteur ATLAS et plus généralement de l’ensemble expérimental est donnée. Le troisième chapitre traite d’une des mesures des performances du calorimètre électromagnétique ATLAS, à savoir l’étude des efficacités identification électronique à l’aide de W se désintégrant en électrons et neutrinos.Dans les chapitres suivants, le coeur de cette thèse, la recherche et l’étude de la production associée de boson de Higgs avec une paire de quark top, appelée production ttH, est traitée dans le schéma du modèle Standard et au-delà. L’observation de la production ttH avec le détecteur ATLAS a été récemment annoncée en 2018 et représente une étape importante pour le domaine de la physique des hautes énergies. Afin d’élargir le spectre de cette analyse tth au-delà du SM, cet état final du canal 4L a aussi été étudié dans le cadre de la recherche de bosons de Higgs doublement chargés se désintégrant en W$^{\pm}$W$^{\pm}$, H$^{\pm \pm} \rightarrow $ W$^{\pm}$W$^{\pm}$. En conclusions, les perspectives sur les futurs résultats scientifiques dans le modèle Standard (SM) ainsi que au-delà de SM (BSM) qui pourraient être atteint en utilisant les statistiques complètes des Run1 et Run2 combinés sont donnésThe scientific work presented in this thesis is based on proton proton collision produced, at 13 TeV in the center of mass, created by the Large Hadron Collider (LHC) and recorded between 2015 and 2017 by the ATLAS detector.After a short introduction on the physics program at LHC, the first chapter gives a comprehensive overview of the theoretical context and motivation. Then a complete description of the ATLAS detector and more generally the experimental setup is given with a highlight on the different physics objects used in this research.The third chapter is dealing with a measure of the performances of the ATLAS electromagnetic calorimeter, namely the study of the electron identification efficiencies using W decaying into electrons and neutrinos events.In the following chapters, the core of this thesis work, the search and study of the associated Higgs boson production with top quark pair, so-called ttH production, within the Standard Model schema and beyond is treated. The observation for ttH production with the ATLAS detector recently announced in 2018 represents a significant milestone for the High-Energy Physics field. In order to broaden the spectrum of this ttH analysis beyond the SM, this 4L channel final states was also studied in the context of the search for doubly charged Higgs boson decaying into W±W±, H±±→W±W±.In conclusions, future prospects in Standard Model (SM) as well as Beyond SM (BSM) scientific results that could be reached using the full Run1 and Run2 combined available statistics are given
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Edwards, Valerie 1954. „The new role of labor unions as developers of responsive dependent care benefit programs : extending dependent care benefits to the independent contractor, freelancer and self-employed worker : a study of professional freelance musicians from Boston Musicians' Association Local 9-535“. Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/65668.
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Ruckert, Benjamin. „Search for a Higgs Boson Produced in Association with a W Boson at ATLAS“. Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-108382.
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6
Le, Quilleuc Eloi. „Etude de la production de boson de Higgs en association avec une paire de quarks top-antitop dans l'expérience ATLAS“. Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS205/document.
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J'ai pris part à la recherche du boson de Higgs dans l'expérience ATLAS avec l'étude de l'état final comprenant une paire de quark top anti-top accompagnée d'un boson de Higgs, dit ttH. Je me suis spécialisé sur le canal boostés, dans lequel quarks top et boson de Higgs sont émis à haute énergie.La mesure de la section efficace du processus physique pp -> ttH permet de tester la validité du Modèle Standard de la physique des particules, qui prédit le mécanisme d'interaction entre quark top et boson de HiggsI took part in the Higgs boson search in the ATLAS experiment with the study of the final state of a top anti-top quark pair accompanied by a Higgs boson, called ttH. I have been focused on the boosted channel, in which top quarks and Higgs bosons are emitted at high energy.The measurement of the cross-section of the physical process pp -> ttH enables to test the validity of the Standard Model of particle physics, which predicts the mechanism of interaction between quark top and Higgs boson
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Slaunwhite, Jason M. „Search for the Higgs Boson Produced in Association with a W Boson at CDF Run II“. The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1232121462.
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Fiascaris, Maria. „W Boson production in association with hadronic jets at ATLAS“. Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543477.
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Sawyer, Craig Anthony. „Measurements of vector boson production in association with jets at the LHC using the ATLAS detector“. Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:9c8f606b-4b66-4a42-a200-11cf81ea84f0.
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This thesis presents measurements of the cross section for the production of a W boson in association with jets and the ratio of the cross sections for the production of a W boson and a Z boson in association with jets. Both measurements are performed in proton-proton collisions at √s = 7 TeV with the ATLAS experiment at the Large Hadron Collider using a dataset corresponding to an integrated luminosity of 4.6 fb-1. The dataset allows for the exploration of a large kinematic range, including jet production up to a transverse momentum of 1 TeV and multiplicities up to seven jets. Results are presented as a function of jet transverse momenta and rapidities and as a function of event variables such as the scalar sum of the transverse momenta of the jets. Results as a function of dijet angular variables are also presented. The measurements are compared to several state-of-the-art QCD predictions including next-to-leading-order perturbative calculations, resummation calculations and Monte Carlo generators. Finally, the effect of the results on parton distribution functions is explored.
10
Wright, Michael. „Higgs production in association with a Z boson at the LHC“. Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5754/.
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The associated Z vector boson production rate of the Standard Model Higgs boson has been measured in decays into two b quarks, with the Z boson decaying into an electron or muon pair in the ATLAS detector at the Large Hadron Collider (LHC). The associated Z vector boson production cross section in the Standard Model is almost two orders of magnitude smaller than the dominant Higgs boson production cross section from gluon fusion. Proton-proton collision data at a centre-of-mass energy of 8 TeV delivered by the LHC with the ATLAS detector corresponding to an integrated luminosity of 13 fb−1 has been analysed. A Higgs boson produced via associated production with a Z vector boson is excluded with a 95% confidence level in a mass range between 110 to 130 GeV at 6 to 11 times the Standard Model cross section, respectively.
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Barnovska, Zuzana. „Diphoton measurements with the ATLAS detector at LHC : search for new resonances and study of diphoton production in association with jets“. Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY072/document.
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Cette thèse étudie les collisions pp à sqrt{s} = 8 TeV avec des paires de photons dans l'état final, telles que recueillies par l'expérience ATLAS au LHC au cours de 2012. L'état final avec diphoton s'est avéré cruciale pour la découverte du boson de Higgs. La motivation pour la recherche de résonances supplémentaires se désintégrant en deux photons est très forte en raison l'existence de nombreux modèles prévoyant un secteur de Higgs étendu. Dans le même temps, des mesures détaillées des sections efficaces diphoton sont nécessaires pour établir la précision des prédictions théoriques actuellement disponibles pour ces processus.La mesure des photons par ATLAS repose sur un excellent étalonnage de la réponse du calorimètre électromagnétique. Pour cette raison, les études liées à l'étalonnage de la réponse de photons dans le calorimètre Argon Liquide (LAr) sont initialement réalisées, y compris la mesure de l'étalonnage par rapport à l'échelle de l'énergie de la couche calorimètre utilisant des photons, et la nécessité éventuelle d'un inter-étalonnage de la réponse en énergie des photons en fonction de l'angle azimutal $phi$. Une étude de l'amplitude du bruit du calorimètre dans des conditions de pile-up élevés est également présentée, aboutissant à des recommandations pour les configurations d'échantillonnage d'impulsion LAr au Run2.La recherche d'une résonance supplémentaire se désintégrant en deux photons est effectuée et aucun signal n'est observé: une limite est mise sur la section efficace fiducielle d'une résonance multipliée par son rapport de branchement de désintégration en diphoton. La mesure de la section efficace de production de diphoton isolés en association avec des jets est effectuée en fonction de la masse invariante de diphoton, l'impulsion transverse du système diphoton, la différence d'angles dans le plan azimutal de l'angle entre les deux photons et l'angle theta de coplanarité, en fonction de la multiplicité en jets et de différentes variables associés aux jets. Les résultats sont comparés aux dernières prévisions QCD Next-To-Leading-Order QCD. Une telle mesure est la première du genre effectuée au LHCThis thesis studies pp collisions at sqrt{s}=8 TeV with pairs of photons in the final state, as collected by the ATLAS experiment at the LHC during 2012. The diphoton final state has proven to be crucial to the discovery of the Higgs boson. The motivation for searching for additional resonances decaying into two photons is very strong due to many models predicting an extended Higgs sector. At the same time, detailed measurements of diphoton cross sections are necessary to establish the quality of the theoretical predictions currently available for these processes.The measurement of photons by ATLAS relies on an excellent calibration of the electromagnetic calorimeter response. For this reason, studies related to the calibration of the photon response in the ATLAS Liquid Argon (LAr) calorimeter are initially performed, including a measurement of the calorimeter layer energy scale relative calibration using photons, and the potential need of an inter-calibration of the photon energy response as a function of the azimuthal angle $phi$. A study of noise performance of the calorimeter in high pile-up conditions is also presented, resulting in recommendations for the LAr pulse sampling configurations for Run2.A search for an additional resonance decaying into two photons is performed, leading to no significant excess being observed. A limit on the fiducial cross section times branching fraction of a new resonance decaying into two photons is therefore computed. The measurement of the production cross section of isolated prompt diphoton in association with jets is performed as a function of the diphoton invariant mass, the transverse momentum of the diphoton system, the azimuthal angle difference of the two photons and the coplanarity angle theta, for jet multiplicity categories and as a function of various jet variables. The results are compared to the latest Next-To-Leading-Order QCD predictions. Such a measurement has not been previously published at the LHC
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Lopez, Solis Alvaro. „Contribution à la mesure d’énergie et du temps des électrons et des photons dans l’expérience ATLAS et recherche de la production de matière noire en association avec un boson de Higgs“. Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066372.
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La découverte d'une particule cohérent avec la production d'un boson de Higgs du Modèle Standard (MS) en 2012 par les collaborations ATLAS et CMS a ouverte de nouvelles possibilités de recherche de physique au-delà du MS (BSM). Les recherches de matière noire en ATLAS se concentrent sur des modèles générales, appelées mono-X, qui prédisent la production d'un seul objet X (jet, photon ou des bosons W ou Z) en association à des particules de matière noire (DM). La production de ces états finaux dépend du couplage entre les objets radiés et les particules en collision. Ce fait encourage la recherche des signaux mono-Higgs car le boson de Higgs ne se couple pas directement avec des gluons et ses couplages avec les quarks légères sont très faibles. Par conséquent, le Modèle Standard ne prédit pas une grande contribution à ces états finaux, donc toute déviation observée des prédictions du MS permettrait d'étudier directement le couplage du boson de Higgs à des nouveaux secteurs BSM. Lors de cette thèse, une recherche a été menée sur la production des particules de matière noire en association à un boson de Higgs se désintégrant en deux photons. En ayant pour but d'augmenter la sensibilité de l'expérience à une possible découverte, des études sur l'effet de diaphonie ont été menées afin d'améliorer l'identification de photons dans ATLAS. Par ailleurs, les particules de matière noire n'interagissent pas avec le détecteur, ce qui impose des signatures avec une grande énergie transverse manquante. Des études sur la performance de la reconstruction de cette énergie transverse manquante ont été mises en place pour des topologies contenant un boson de Higgs se désintégrant en deux photonsThe discovery of a particle consistent with a Standard Model (SM) Higgs boson in 2012 by the ATLAS and CMS collaborations has opened up new possibilities in searches for physics beyond the SM (BSM). Searches for dark matter in ATLAS focus on a special case of general models called, mono-X, that predict a single object X (jet, photon, W or Z bosons) produced in association to dark matter (DM) particles. The production of these final states depend on the coupling between the radiated object and the colliding particles. This fact motivates the search of mono-Higgs signals since Higgs does not couple to gluons and its couplings to light quarks are very weak. Then, the Standard Model does not predict a large contribution to these mono-Higgs final states, thus any deviation from SM predictions is a direct probe of a coupling between the Higgs and a new BSM sector. A search of DM particles produced in association to a Higgs boson decaying into two photons has been carried out in this thesis. Aiming to increase the significance of discovery in this channel, studies on the cross-talk effect has been performed to improve photon identification in ATLAS. Besides, DM particles are not expected to interact within the detector fiducial volume, thus predicted signatures include a large missing transverse momentum. Performance studies of the reconstruction of this missing momentum has been put in place in topologies containing a Higgs boson decaying into two photons
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Rodina, Yulia. „Search for the Higgs boson decaying to a pair of bottom quarks and produced in association with a pair of top quarks in the LHC Run 2 data with the ATLAS detector using a likelihood technique“. Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/458630.
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Yang, Xuan. „Mesure de la production du boson de Higgs standard en association avec une paire de quarks top et antitop et recherche d'un boson de Higgs chargé se désintégrant en une paire de quarks top et bottom à l'aide du détecteur ATLAS au LHC“. Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALY015.
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Le champ Higgs joue un rôle important dans le modèle standard (SM). Il est non seulement responsable de la génération des particules élémentaires, mais aussi du seul champ scalaire du SM. L'étude du boson de Higgs est devenu l'un des sujets les plus populaires au LHC. Il fournit une excellente occasion de sonder les prédictions du SM et de rechercher des signes de nouvelle physique. La nouvelle physique au-delà du SM a généralement un scénario de Higgs plus compliqué et prévoit plus d'un boson de Higgs, et en particulier des bosons de Higgs chargés. La recherche de ces nouvelles particules nous donnera un aperçu direct de la nouvelle physique.Dans cette thèse, deux contributions principales sont présentées : la recherche d'un boson de Higgs lourd et chargé (H +) se désintégrant en t b et la recherche de la production de t t H dans les états finaux multileptoniques. La recherche de H + est réalisée sur les données collectées par le détecteur ATLAS en 2015 et 2016, correspondant à une luminosité intégrée de 36,1 fb-1. Aucun excès significatif de signal H + au-dessus des bruits de fond du SM n'a été observé dans la gamme de masse de 200 GeV à 2000 GeV. La plus grande déviation de l'hypothèse SM seule, obtenue à partir de l'ajustement est observée à 300 GeV, correspondant à une valeur locale de p0 de 1,13%. La recherche de la production de t t H dans l'état final multileptonique est réalisée avec des données collectées au cours de la période 2015-2017, correspondant à une luminosité intégrée de 79,9 fb-1. Le couplage Yukawa du boson de Higgs et du quark top peut être directement déterminé à partir de la mesure de la section efficace de production de t t H. Cette analyse vise l'observation de la production de t t H en utilisant uniquement des états finaux multileptoniques. Il existe six états finaux définis par le nombre de leptons légers (électrons ou muons) et de taus hadroniques, et 25 catégories d'événements pour rechercher le signal t t H et estimer les faux leptons simultanément. Les études de l'état final avec deux leptons de même signe et un tau hadronique sont discutées en détail. Un excès d'événements t t H par rapport aux autres processus du SM est observé avec une significance observée (attendue) de 1,8 σ (3,1 σ). La section efficace de production de t t H mesurée est de 294 (+ 182 / -162) fb, ce qui est cohérent avec la prédiction SMThe Higgs field plays an important role in the Standard Model (SM). It is not only responsible for elementary particles generation but also the only scalar field in the SM. Hence study of the Higgs boson becomes one of the most popular topics at LHC. It provides a great opportunity to probe the SM predictions and search for beyond SM evidence. New physics beyond the SM usually has a more complicated Higgs scenario and predict more than one Higgs boson, such as a charged Higgs boson. Searching for these new particles will give us a direct hint of new physics.In this thesis, two main contributions are presented, searching for a heavy charged Higgs boson (H +) decaying to t t H and searching for H + production in multilepton final states. The search for H + is performed with data collected by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb-1. There is no significant excess of H + signal over the SM backgrounds observed in the mass range from 200 GeV to 2000 GeV. The largest deviation from the SM hypothesis obtained from the fit is observed at 300 GeV, corresponding to a local p0 de 1,13%. The search for t t H prodcution in multilepton final state is performed with data collected during 2015-2017, corresponding to an integrated luminosity of 79.9 fb-1. The Yukawa coupling of the Higgs boson and top quark can be directly determined from the measurement of t t H production cross section. This analysis aims at observation of t t H production using only multilepton final states. There are six final states defined by the number of light leptons (electrons or muons) and hadronic taus, and 25 event categories to search for t t H signal and estimate fake leptons simultaneously. The studies in the final state with two same-sign leptons and one hadronic tau is discussed in detail. An excess of t t H events over other SM backgrounds is found with an observed (expected) significance of 1,8 σ (3,1 σ). The measured t t H production cross section is 294 (+ 182 / -162) fb, which is consistent with the SM prediction
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Mercurio, Kevin. „A Search for the Higgs Boson Produced in Association With a Vector Boson Using the ATLAS Detector at the LHC“. Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:14226092.
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This dissertation presents two searches for the Standard Model Higgs boson produced in association with a vector boson and decaying via $H\to b\bar{b}$. Specifically, the processes are: \llbb\ alone, and again in combination with the \vvbb\ and \lvbb\ processes. The dataset used for the analysis consists of 4.7 fb$^{-1}$ at $\sqrt{s} = $7~TeV and 20.3 fb$^{-1}$at $\sqrt{s} = $8~TeV from LHC collisions. The search was optimized without bias to a particular mass of the Standard Model Higgs boson.
Background processes contributing to the total number of observed events are estimated using a combination of Monte Carlo simluation and data-driven techniques. Utilizing a maximum-likelihood analysis, an observed upper limit on the cross section at the 95\% confidence interval for the \llbb\ channel is set at 2.76 times the Standard Model cross section with an expected limit of 2.54, and the observed upper limit for the combined search is 2.3 times the Standard Model cross section, with an expected limit of 1.01. Furthermore, compatibility with the Standard Model expectation is evaluated through the parameter $\mu$ = $\frac{\sigma_{observed}}{\sigma_{Standard Model}}$ and found to be $0.17\pm1.4$ for the \llbb\ analysis, and $1.09\pm0.61$ for the combined analysis, both consistent with the Standard Model expectation of 1.
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Leggat, Duncan. „Study of single top quarks in association with vector bosons“. Thesis, Brunel University, 2015. http://bura.brunel.ac.uk/handle/2438/11557.
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Calvet, Thomas. „Search for the production of a Higgs boson in association with top quarks and decaying into a b-quark pair and b-jet identification with the ATLAS experiment at LHC“. Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0312/document.
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En Juillet 2012, les expériences ATLAS et CMS annoncent la découverte d'une nouvelle particule de masse 125 GeV, compatible avec le boson de Higgs prédit par le Modèle Standard. Pour établir la nature de ce boson de Higgs et la comparer au Modèle Standard, il est nécessaire de mesurer le complage du boson de Higgs au fermions. En particulier le quark top possède le plus fort couplage de Yukawa avec le boson de Higgs. Ce couplage est accessible par le processus de production d'un boson de Higgs en association avec une paire de quarks tops (ttH). Cette thèse présente la recherche d'évènement ttH où le boson de Higgs se désintègre en deux quark b dans les données du Run 2 recueillies en 2015 et 2016 par le détecteur ATLAS. La composition du bruit de fond ainsi que la mesure du signal ttH dans les données sont obtenues à partir d'un ajustemement statistique des prédictions aux données. Le bruit de fond tt+jets étant la plus grande source d'incertitudes sur le signal, une attention particulière est portée à sa description.La détection des jets issus de quarks b, appelé b-tagging, est primordiale pour l'analyse ttH(H->bb) dont l'état final contient quatre quarks b. Afin d'améliorer la compréhension des performances des algorithmes de b-tagging pour le Run 2, la définition des jets de saveur b dans les simulations Monte Carlo est revisitée. Les algorithmes standards du b-tagging ne permettant pas la différenciation des jets contenant un ou deux quarks b, une methode spécifique à été développée et est présentée dans cette thèseIn July 2012, the ATLAS and CMS experiments announced the discovery of a new particle, with a mass about 125 GeV, compatible with the Standard Model Higgs boson. In order to assess if the observed particle is the one predicted by the Standard Model, the couplings if this Higgs boson to fermions have to be measured. In particular, the top quark has the strongest Yukawa coupling to the Higgs boson. The associated production of a Higgs boson with a pair of top quarks (ttH) gives a direct access to this coupling. The ttH process is accessible for the first time in the Run 2 of the LHC thanks to an upgrade of the detector and the increase of the center of mass energy to 13 TeV. This thesis presents the search for ttH events with the Higgs boson decaying to a pair of b-quarks using data collected by the ATLAS detector in 2015 and 2016. The description of the background and the extraction of the ttH signal in data are obtained by a statistical matching on predictions to data. In particular the tt+jets background is the main limitation to signal sensitivity and is scrutinized.The identification of jets originating from b-quarks, called b-tagging, is a vital input to the search of ttH(H->bb) events because of the four b-quarks in the final state. For Run 2 the definition of b-flavoured-jets in Monte Carlo simulations is revisited to improve the understanding of b-tagging algorithms and their performance. Standard b-tagging algorithms do not separate jets originating from a single b-quark from those originating from two b-quarks. Thus a specific method has been developed and is reviewed in this thesis
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Cruz-Martinez, Juan Manuel. „Next-to-next-to-leading order QCD corrections to Higgs boson production in association with two jets in vector boson fusion“. Thesis, Durham University, 2018. http://etheses.dur.ac.uk/12806/.
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In this thesis the second-order QCD corrections to electroweak production of a Higgs boson in association with two jets through vector boson fusion are considered. This calculation is fully differential in the kinematics of the Higgs boson and of the final state jets. Infrared divergences are regulated using the antenna subtraction method. We detail the implementation of the process in the parton-level Monte Carlo integrator NNLOJET and present inclusive calculations as well as differential distributions for a wide range of observables at different center-of-mass energies.
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Wilson, Jonathan S. „A Search for the Standard Model Higgs Boson Produced in Association with Top Quarks“. The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1324333673.
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King, Robert Steven Beaufoy. „A first measurement of electroweak production of a W boson in association with two jets with the ATLAS detector“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:4d3ac65d-3f94-4847-806c-5c41a77d3a80.
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A first measurement of Electroweak W + 2 jets production at high dijet mass is performed using sqrt(s) = 7 TeV pp collision data from the Atlas experiment corresponding to 4.6 fb−1 of integrated luminosity. The background only hypothesis is excluded with a significance of 4.89-σ. A cross section of σ = 325 ± 6 (lumi) ±32 (stat) +63−70(syst) ±86 (theo) fb is extracted in the fiducial region.
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Proissl, Manuel Daniel. „Dijet invariant mass studies in the Higgs boson H→bb- resonance search in association with a W/Z boson using the ATLAS detector“. Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10516.
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The Standard Model of Particle Physics describes the fundamental building blocks of matter and phenomena up to the highest particle interaction energies. The theory demands the existence of a scalar particle: the Higgs boson. The Higgs boson was discovered by the ATLAS and CMS collaborations at CERN using bosonic final states and is measured to have a mass of around 125 GeV. This particle is predicted to decay predominantly into pairs of b-quarks at this mass, but suffers from overwhelming backgrounds from the multijet production expected from QCD interactions. Therefore, H→bb- production in association with a leptonically decaying W or Z boson is considered, with Z → vv-, W → lv and Z → ll, where ` denotes electrons and muons. This thesis presents a search for the Higgs boson decaying into bb- pairs in association with a W or Z boson using the ATLAS detector at the Large Hadron Collider (LHC) at CERN. The analysis uses the full dataset recorded during pp collisions at the LHC in Run-1, corresponding to 4.7 fb-1 at √s = 7 TeV and 20.3 fb-1 at √s = 8 TeV. A multivariate technique and a kinematic cut-based approach have been used to maximize the signal over background ratio, where a particular emphasis on the latter approach is made in this thesis. Final state radiation and reconstruction effects may decrease the bb- resonance resolution significantly, while comparably decreasing the probability of observing the decay over the background. The b quark pairs from the Higgs boson are reconstructed as topological clusters formed to jets in the ATLAS calorimeter. Thus, the reconstruction and calibration of these jets are crucial for the final Higgs mass resolution and paramount for the search and for future precision measurements of V H, H→bb- production. This thesis presents the development and evaluation of advanced techniques to improve the invariant dijet mass reconstruction of the H→bb- candidate. Sequential jet calibrations, semileptonic corrections and pT corrections to account for the interplay between jet resolution/scale and the underlying signal pT spectrum obtained from Monte Carlo simulations have been studied. A major focus has been made on the development and evaluation of an event-level kinematic likelihood fitting framework to exploit the full kinematic potential of V H topologies within the detector uncertainties of the reconstructed final state signatures in order to improve the measurement of the b-tagged jet kinematics. The jet energy calibrations of the H→bb- signal candidates yield an overall improvement of the dijet invariant mass resolution of up to ~30%, and of the expected statistical significance of ~12%. The analysis procedure is validated using the resonant V Z(bb-) production in the same final states as for the Higgs boson search, and is observed, compatible with the Standard Model expectation, with a significance of 4.9 standard deviations and a signal strength of μ^V Z = 0:74+0:17 -0:16. For a Higgs boson mass of 125.36 GeV, the observed (expected) deviation from the background-only hypothesis is found with a significance of 1.4 (2.6) standard deviations and a signal strength is determined to be μ^V H = 0:52±0:32(stat.)±0:24(syst.).
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Anger, Felix Richard [Verfasser], und Harald [Akademischer Betreuer] Ita. „NLO QCD corrections to vector boson production in association with multiple heavy and light jets“. Freiburg : Universität, 2018. http://d-nb.info/1158495706/34.
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Coubez, Xavier. „Search for the standard Higgs boson produced in association with a pair of top quark in the multi-leptons channel in the CMS experiment“. Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE049/document.
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La découverte en 2012 de la dernière particule élémentaire prédite par le Modèle Standard, le boson de Higgs, a ouvert une nouvelle ère en physique des particules. L’un des objectifs est désormais de sonder les couplages du boson de Higgs aux autres particules afin de confirmer la validité du modèle. Le travail de cette thèse a porté dans un premier temps sur l’identification de jets issus de quark b dès le système de déclenchement. L’objectif est de permettre de sélectionner un millier d’événements parmi les quarante millions produits chaque seconde au LHC en identifiant des objets présents dans l’état final de processus de physique intéressants tels que la production associée d’un boson de Higgs se désintégrant en paire de quark b avec un boson Z se désintégrant en neutrinos non détectés. Dans un second temps, l’étude du couplage du boson de Higgs au quark top, particule la plus massive au sein du Modèle Standard a été réalisée. Après l’étude d’un bruit de fond important de la production associée d’un boson de Higgs et d’une paire de quarks top, une nouvelle méthode a été utilisée pour améliorer la discrimination entre le signal et les principaux bruits de fond. Cette analyse a conduit à la première évidence expérimentale du couplage entre le boson de Higgs et le quark topThe discovery in 2012 of the last elementary particle predicted by the Standard Model, the Higgs boson, has opened a new era in particle physics. One of the objectives now is to probe the coupling of the Higgs boson to other particles in order to confirm the validity of the model. The work of this thesis focused initially on the identification of jets coming from b quark at trigger level. The goal is to allow for the selection of one thousand events among the forty million produced every second at the LHC, by identifiying objects present in the final states of interesting physics processes such as the associated production of a Higgs boson decaying in a pair of b quark with a Z boson decaying into undetected neutrinos. The work then moved to the study of the coupling of the Higgs boson to the quark top, most massive particle in the Standard Model. After a study of one of the important background of the associated production of the Higgs boson and a top quark pair, a new method called matrix element method has been used to improve the discrimination between signal and background. This analysis has led to the first experimental evidence of coupling between the Higgs boson and the top quark
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Al, Khoury Konie. „Measurements of the Higgs boson produced in association with a vector boson and decaying to a pair of b-quarks with the ATLAS detector“. Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP006.
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La découverte du boson de Higgs en 2012 par les expériences ATLAS et CMS a ouvert tout un nouveau domaine de recherche au LHC: la mesure des propriétés de cette particule permet d’affiner notre compréhension du Modèle Standard et de contraindre la physique au-delà de ce Modèle. Cette thèse présente les mesures du boson de Higgs se désintégrant en une paire de quarks-b et produit avec un boson W ou Z, réalisées en utilisant 139fb⁻¹ de données de collisions proton-proton à une énergie de 13 TeV dans le centre de masse collectées par le détecteur ATLAS. Trois canaux sont définis, nommés 0-, 1- et 2-leptons, selon le nombre de leptons chargés provenant de la désintégration du boson vecteur. L’analyse bénéficie de la grande statistique des données Run-2 et de l’amélioration de nombreuses techniques d’analyses, ce qui accroît sa sensibilité et permet l’observation du signal ZH et une preuve solide du signal WH dans cette désintégration du boson de Higgs en paires de quarks-b. Des mesures de sections efficaces différentielles sont également menées, et sont en bon accord avec la théorie. Le détecteur ATLAS fera l’objet de nombreuses mises à jour en vue de l’exploitation du HL-LHC afin de pouvoir tolérer l’augmentation de la luminosité et du niveau d’empilement. L’électronique de lecture du calorimètre à argon liquide sera ainsi remplacée. Une partie de cette thèse est consacrée à vérifier si les prototypes de préamplificateurs Front-End proposés pour la mise à jour sont conformes aux exigences physiquesThe discovery of the Higgs boson in 2012 by the ATLAS and CMS experiments has opened a new research domain at the LHC, with the measurement of the properties of this particle to refine our understanding of the Standard Model and constrain physics beyond this model. The measurements of the Higgs boson decaying to a pair of b-quarks and produced alongside a W or Z boson, performed with the ATLAS detector using 139 fb⁻¹ of data collected in proton-proton collisions at a center-of-mass energy of 13TeV are presented in this thesis. Three channels are defined, the 0-, 1- and 2-lepton channels, depending on the number of charged leptons coming from the decay of the vector boson. The analysis takes advantage of the full Run-2 data statistics and of the improvement of many analysis techniques, which increases its sensitivity and allows the observation of the ZH signal and a strong evidence of the WH signal in this decay channel of the Higgs boson into pairs of b-quarks. Differential cross-section measurements are also performed and are found to be in good agreement with the Standard Model. The ATLAS detector will undergo many upgrades in preparation for the HL-LHC operation to be able to cope with the increase in luminosity and pile-up level. Therefore the liquid argon calorimeter readout electronics will be replaced. A part of this thesis is dedicated to check if the Front-End pre-amplifier prototypes proposed for the upgrade comply with the physics requirements
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Williams, Ciaran. „Hadronic productions of a Higgs boson in association with two jets at next-to-leading order“. Thesis, Durham University, 2010. http://etheses.dur.ac.uk/414/.
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We present the calculation of hadronic production of a Higgs boson in association with two jets at next-to-leading order in perturbation theory. We consider amplitudes in an effective theory in which the Higgs couples to gluons in the limit of a large top quark mass. We treat the Higgs as the real part of the complex field φ that couples to the self-dual field strengths. We use modern on-shell inspired methods to calculate helicity amplitudes and we give a detailed review of unitarity based and on-shell methods. Using these unitarity methods we derive the cut-constructible pieces of the general φ-MHV amplitudes in which the positions of the two negative gluons are arbitrary. We then generate the cut-constructible pieces of the φ-NMHV four parton amplitudes. We generate the rational pieces of these amplitudes and the four-gluon φ-MHV amplitude using Feynman diagrams. For the φ-MHV amplitude we also use the unitarity-boostrap method to calculate the rational pieces. We then implement these, and analytic results from previous calculations, into MCFM. Using this program we are able to perform some phenomenological studies at the Tevatron and LHC.
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Smart, Ben Harry. „Search for the Standard Model Higgs boson produced in association with a vector boson and decaying to a b-quark pair with the ATLAS detector“. Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/14184.
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An important question at present in particle physics is whether the recently discovered boson with a mass of about 125 GeV is the Standard Model Higgs boson. A Standard Model Higgs boson with a mass of 125 GeV will predominantly decay to b-quark pairs. This work presents the author's contribution to the search with the ATLAS detector for a Standard Model Higgs boson produced in association with a W or Z boson and decaying to b-quark pairs. In order to search for the decay modes ZH → vvb¯b, WH → lvb¯b and ZH → l¯lb¯b, where l is either an electron or muon, events with zero, one or two electrons or muons are considered in 20:3 fb¯1 of 8 TeV LHC data. A Standard Model Higgs boson is not observed decaying to b-quark pairs, although neither is this decay mode ruled out. A Standard Model Higgs boson with a mass of between 110 GeV and 115 GeV is excluded. For mH = 125 GeV the observed (expected) upper limit on the cross- section times the branching ratio is found to be 2.16 (1.07) times the Standard Model prediction. For a Standard Model Higgs boson with a mass of 125 GeV, the best fit signal strength is μ = 1:09 +0:43-0:42 (stat) +0:44-0:37 (syst) = 1:09 +0:61-0:56. The combined results are consistent with a Standard Model Higgs boson with a mass of 125 GeV. The author's own work is presented, including estimation of systematic uncertainties on WH → lvb¯b modelling, and future ATLAS data selection methods for WH → lvb¯b searches. Overviews of underlying theoretical matters and the experimental facilities used are given.
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Kucher, Inna. „Search for the Higgs boson decaying to two photons and produced in association with a pair of top quarks in the CMS experiment“. Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS181/document.
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Dans cette thèse, la mesure des propriétés du boson de Higgs dans le canal de désintégration en deux photons avec l'expérience CMS au Grand Collisionneur de Hadrons (LHC) est présentée. L'objectif de ce travail est l’étude du mode de production associé à une paire de quark top (tṫH). Ce mode représente le seul accès direct au couplage de Yukawa du quark top, un paramètre fondamental du Modèle Standard. Le mode de production tṫH est un processus très rare. Il est de l'ordre de deux ordres de grandeur plus petits que la production principale du boson de Higgs par fusion de gluons. À 13 TeV, le mode de production ttH est environ 4 fois plus grand qu'à 8 TeV. Cette thèse reprend les études réalisées à 8 TeV, où l’échantillon de données ne suffisait pas pour établir une observation de ce mode de production. Bien que le canal en deux photons ne soit pas celui qui présente le plus grand rapport de branchement (seulement 0,2%), il est très prometteur en raison de son excellente résolution en masse (1%). De plus, sa signature est très propre dans le détecteur. Le canal de désintégration en deux photons est particulièrement intéressant puisqu'il s'agit du seul canal permettant l'étude de tous les modes de production : la fusion de gluons, la fusion de bosons vecteurs, les productions associées avec des bosons W ou Z ou avec une paire de quarks top. Le document commence par une introduction théorique du Modèle Standard et la physique du boson de Higgs au LHC, suivie d'une description du détecteur CMS. Pour obtenir une excellente résolution de masse dans le canal de désintégration en deux photons , le calorimètre électromagnétique doit être calibré. Le système de monitorage de la transparence des cristaux du calorimètre électromagnétique de CMS par le système laser joue un rôle important dans la chaîne d'étalonnage et est décrit en détail. Sur le long terme, le système de monitorage laser devra être amélioré car le niveau de rayonnement influence son électronique. Je présente mon travail sur l'amélioration possible du système de monitorage laser, ainsi que l'étude de sa précision possible. L'analyse inclusive H → ᵞᵞ a eu plusieurs itérations pour les conférences en 2016 et 2017. La stratégie pour 2017 est décrite dans ce document. Une classification des événement sert à maximiser la significance du signal et à étudier les modes spécifiques de production du boson de Higgs. Mes contributions à l'analyse H → ᵞᵞ consistent en l'identification du vertex primaire, l'identification du photon et l'étude du mode de production tṫH. Chaque contribution est décrite en détail dans des chapitres dédiés. L'analyse tṫH, H → ᵞᵞ est présentée pour deux itérations en 2016 et 2017, en mettant l'accent sur les améliorations dans l'analyse de 2017. Enfin, les résultats de l'analyse inclusive et tṫH, H → ᵞᵞ, en utilisant l'ensemble complet de données 2016 correspondant à une luminosité intégrée de 35,9 fb-1, sont présentésIn this thesis, the measurement of the Higgs boson properties in the diphoton decay channel with the CMS experiment at the Large Hadron Collider (LHC) is presented. The focus of this work is the tṫH production mode, as it is the only direct access to the top quark Yukawa coupling, a fundamental parameter of the Standard Model. tṫH is a very rare process, two orders of magnitude smaller than the dominant Higgs boson production by gluon fusion. At 13 TeV, ttH production is about 4 times larger than at 8 TeV. This thesis takes over the studies performed at 8 TeV, where the statistics was not enough for an observation of ttH. Despite a very small branching ratio (only about 0.2%), the two photons decay channel of the Higgs boson is very promising, because of its excellent mass resolution (about 1%). Moreover, its signature in the detector is very clear. The diphoton decay channel is also of particular interest as it is the only channel allowing the study of all production modes: gluon fusion, vector boson fusion, associated productions with a W or a Z bosons, or with a top quark pair.The document starts with a theoretical introduction about the Standard Model and Higgs boson physics at LHC, followed by a description of the CMS detector. To achieve an excellent mass resolution in the H → ᵞᵞ channel, the electromagnetic calorimeter has to be calibrated. The laser monitoring system plays an important role in the calibration chain and it is described in details. On the long term, the laser monitoring system will have to be upgraded as level of radiation influences its electronics. I present my work on the possible upgrade of the laser monitoring system, along with the study of its possible precision.H → ᵞᵞ inclusive analysis had several iterations for conferences in 2016 and 2017. The strategy for 2017 is described in this document. An event classification is used to maximize the signal significance and to study specific Higgs boson production modes. My contributions to the H → ᵞᵞ analysis are primary vertex identification, photon identification and the study of the tṫH production mode. Each contribution is described in details in dedicated chapters. The tṫH, H → ᵞᵞ analysis is shown for two iterations in 2016 and 2017, with the emphasis on improvements in 2017 analysis. Finally, the results of the inclusive and tṫH, H → ᵞᵞ analysis, using the full 2016 dataset corresponding to an integrated luminosity of 35.9 fb-1, are shown
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Flowers, Sean Christopher. „Search for the Standard Model Higgs boson produced in association with top quarks in the lepton plus jets channel“. The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu150043192139632.
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Ucchielli, Giulia. „Multivariate analysis methods in the search for the Higgs boson produced in association with top pairs at the ATLAS experiment at LHC“. Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7607/.
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The Large Hadron Collider, located at the CERN laboratories in Geneva, is the largest particle accelerator in the world. One of the main research fields at LHC is the study of the Higgs boson, the latest particle discovered at the ATLAS and CMS experiments.
Due to the small production cross section for the Higgs boson, only a substantial statistics can offer the chance to study this particle properties. In order to perform these searches it is desirable to avoid the contamination of the signal signature by the number and variety of the background processes produced in pp collisions at LHC.
Much account assumes the study of multivariate methods which, compared to
the standard cut-based analysis, can enhance the signal selection of a Higgs
boson produced in association with a top quark pair through a dileptonic
final state (ttH channel).
The statistics collected up to 2012 is not sufficient to supply a significant
number of ttH events; however, the methods applied in this thesis will provide a powerful tool for the increasing statistics that will be collected during the next LHC data taking.
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Allbrooke, Benedict Marc Miller. „Search for the Higgs Boson decaying to a b quark pair produced in association with a W Boson using missing transverse energy triggered events at ATLAS“. Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5681/.
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The WH → \(lv\)bb production and decay mode of the standard model Higgs Boson is searched for using the 2012 LHC proton-proton data recorded by the ATLAS detector at a centre-of-mass energy √s=8 TeV. Events containing W → μ\(v\) that fail muon triggers are recovered using a novel technique of recording these events with missing transverse energy based triggers. Two analyses are employed, one based on simple selection criteria to enhance the signal-to-background ratio and one that uses more complex multivariate techniques to separate signal from background. Both analyses exploit the different signal-to-background ratios in regions of the reconstructed W transverse momentum and b-jet tagging categorisation. The events recorded using the missing transverse energy triggers are analysed exclusively as well as merged with the events recorded using lepton triggers to improve the sensitivity of the final analyses. The multivariate merged analysis is found to be the more sensitive of the two analyses, gaining 18.5% compared to the equivalent cut-based analysis. The observed (expected) 95% CL limit for the WH → \(lv\)bb mode is found to be 2.507 (1.369) and the observed (expected) significance is 1.905 (1.534). The final value of the signal strength for WH → \(lv\)bb is μ=1.231± \[^{0.733}_{0.665}\] which is consistent with the Standard Model expectation.
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Alio, Lion. „Search for the higgs boson produced in association with a Z boson and decaying to a pair of bottom quarks with the Atlas experiment at LHC“. Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4055/document.
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Recherche la Higgs boson produit en associe avec a Z boson et desintegre a paire de b-quarks. Cet etude est realise avec l'experience ATLAS aupres du LHC. Cet recherche contient le travail de l'identification de b-jets au detecteur d'ATLAS, l'etude de triggers de l'energie manquant et introduire un nouveau trigger qui permet de gagner plus de significance de signaux. La recherche de Higgs boson est poursuit avec l'implementation de nouveau trigger et faire d'analyse statistique pour estimer la significance gagne en comparaison avec l'analyse qui utilise triggers nominauxSearch for the Higgs poson produced in association with a Z boson and decaying to a pair of b-quarks. This study is implemented with the ATLAS experience at LHC. This research includes the work on identification of b-jets in ATLAS detector, study of triggers of missing transverse energy and introduce a new trigger which is expected to gain more signal significance. The search for the Higgs boson is followed with the implementation of the new trigger and do the statistical analysis to estimate the significance gain in comparison with the analysis which use the nominal triggers
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Wang, Qun. „Measurement of the differential cross section of Z boson production in association with jets at the LHC“. Doctoral thesis, Universite Libre de Bruxelles, 2018. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/271719.
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This thesis presents the measurement of the differential cross section of Z boson pro-duction in association with jets (Z+jets) in proton-proton collision at the center-of-massenergy of 13 TeV. The data has been recorded with the CMS detector at the LHC duringthe year 2015, corresponding to an integrated luminosity of 2.19 fb −1 .A study of theCMS muon High Level Trigger (HLT) with the data collected in 2016 is also presented.The goal of analysis is to perform a first measurement at 13 TeV of the cross sections ofZ+jets as a function of the jet multiplicity, its dependence on the transverse momentumof the Z boson, the jet kinematic variables (transverse momentum and rapidity), thescalar sum of the jet momenta, and the balance in the transverse momentum betweenthe reconstructed jet recoil and the Z boson. The results are obtained by correctingthe detector effects, and are unfolded to particle level. The measurement are com-pared to four predictions using different approximations: at the leading-order (LO),next-to-leading-order (NLO) and next-to-next-to-leading order (NNLO) accuracy. Thefirst two calculations used M AD G RAPH 5_ A MC@NLO interfaced with PYTHIA 8 for theparton showering and hadronisation, one of which includes matrix elements (MEs) atLO, another includes one-loop corrections (NLO). The third is a fixed-order calculationwith NNLO accuracy for Z+1 jet using the N -jettiness subtraction scheme (N jetti ). Thefourth uses the GENEVA program with an NNLO calculation combined with higher-order resummation.A series of studies on the HLT double muon trigger are also included. Since 2015 theLHC reached higher luminosity, more events are produced inside the CMS detector persecond, which resulted in more challenges for the trigger system. The work presentedincludes the monitoring, validation and the calibration of the muon trigger paths since2016.Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Buzatu, Adrian. „Search for the standard model Higgs Boson produced in association with a W Boson in the isolated-track charged-lepton channel using the collider detector at Fermilab“. Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104593.
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The Higgs boson is the only elementary particle predicted by the Standard Model (SM) that has not yet been observed experimentally. If it exists, it explains the spontaneous electroweak symmetry breaking and the origin of mass for gauge bosons and fermions. We test the validity of the SM by performing a search for the associated production of a Higgs boson and a W boson in the channel where the Higgs boson decays to a bottom-antibottom quark pair and the W boson decays to a charged lepton and a neutrino (the WH channel). We study a dataset of proton-antiproton collisions at a centre-of-mass energy of 1.96 TeV provided by the Tevatron accelerator, corresponding to an integrated luminosity of 5.7 inverse femtobarns , and recorded using the Collider Detector at Fermilab (CDF). We select events consistent with the signature of exactly one charged lepton (electron or muon), missing transverse energy due to the undetected neutrino (MET) and two collimated streams of particles (jets), at least one of which is required to be identified as originating from a bottom quark. We improve the discrimination of Higgs signal from backgrounds through the use of an artificial neural network. Using a Bayesian statistical inference approach, we set for each hypothetical Higgs boson mass in the range 100 - 150 GeV/c^2 with 5 GeV/c^2 increments a 95% credibility level (CL) upper limit on the ratio between the Higgs production cross section times branching fraction and the SM prediction.Our main original contributions are the addition of a novel charged lepton reconstruction algorithm with looser requirements (ISOTRK) with respect the electron or muon tight criteria (TIGHT), as well as the introduction of a novel trigger-combination method that allows to maximize the event yield while avoiding trigger correlations and that is used for the ISOTRK category. The ISOTRK candidate is a high-transverse-momentum good-quality track isolated from other activity in the tracking system and not required to match a calorimeter cluster, as for a tight electron candidate, or an energy deposit in the muon detector, as for a tight muon candidate. The ISOTRK category recovers real charged leptons that otherwise would be lost in the non-instrumented regions of the detector. This allows the reconstruction of more W boson candidates, which in turn increases the number of reconstructed WH signal candidate events, and therefore improves the sensitivity of the WH search. Since there is no ISOTRK-dedicated trigger at CDF, for the ISOTRK charged lepton category we employ three MET-plus-jets-based triggers using a novel method, which allows the combination of any number of triggers in order to maximize the event yield while avoiding trigger correlations. On an event-by-event basis, only the trigger with the largest efficiency is used. By avoiding a logical "OR" between triggers, the loss in the yield of events accepted by the trigger combination is compensated by a smaller and easier-to-compute corresponding systematic uncertainty. The addition of the ISOTRK charged lepton category to the TIGHT category produces an increase of 33% in the WH signal yield and a decrease of 15.5 % to 19.0 % in the median expected 95 % CL cross-section upper limits across the entire studied Higgs mass interval. The observed (median expected) 95 % CL SM Higgs upper limits on cross section times branching ratio vary between 2.39 x SM (2.73 x SM) for a Higgs mass of 100 GeV/c^2 to 31.1 x SM (31.2 x SM) for a Higgs mass of 150 GeV/c^2, while the value for a 115 GeV/c^2 Higgs boson is that of 5.08 x SM (3.79 x SM).The novel trigger combination method is already in use by several CDF analyses. It is applicable to any analysis that uses triggers based on MET and jets, such as supersymmetry searches at the ATLAS and CMS experiments at the Large Hadron Collider. In its most general form, the method can be used by any analysis that combines any number of different triggers.Le boson de Higgs est la seule particule elementaire predite par le Modele Standard qui n'a jamais ete observee experimentalement. S'il existe, il explique la brisure spontanee de la symetrie electrofaible, ainsi que la masse des bosons W et Z et de tous les fermions. On verifie la validite du Modele standard en effectuant une recherche sur la production associee d'un boson de Higgs et d'un boson W dans le cas ou le boson de Higgs se desintegre en une paire de quarks bottom-antibottom et le boson W se desintegre en un lepton charge et un neutrino (le mode WH). Nos donnees furent accumulees en etudiant des collisions proton-antiproton a une energie au centre de masse de 1.96 Tev produites par l'accelerateur Tevatron, a une luminosite integree de 5.7 femtobarns inverses et collectees par le detecteur Collider Detector at Fermilab (CDF). On selectionne des evenements avec une signature correspondante a exactement un lepton charge (electron ou muon), de l'energie manquante transversale a cause du neutrino qui s'echappe du detecteur (MET) et deux jets de particules, dont au moins un doit provenir d'un quark bottom. On ameliore la discrimination entre le signal Higgs et le bruit de fond a l'aide d'un reseau de neurones artificiels. En utilisant une inference statistique bayesienne, on calcule pour chaque masse hypothetique du boson de Higgs dans l'intervalle 100-150 GeV/c^2, avec des increments de 5 GeV/c^2, une limite superieure de 95% d'intervalle de credibilite (CL), sur le rapport entre la section efficace multipliee par le rapport d'embranchement et celle predite par le Modele Standard. Notre contribution principale est l'introduction d'un nouvel algorithme de reconstruction d'un lepton charge avec des criteres plus laches (ISOTRK) par rapport aux criteres stricts de reconstruction des candidats d'electrons et de muons (TIGHT). La deuxieme contribution majeure consiste en l'introduction d'une nouvelle methode pour combiner des declencheurs differents permetant de maximiser le nombre d'evenements selectionnes et en meme temps que d'eviter les correlations entre les declencheurs.Un candidat de ISOTRK est une trajectoire qui correspond aux criteres de qualite, qui a une large quantite de mouvement transverse, qui est isolee d'autres activites dans le detecteur de trajectoires et qui ne doit pas se prolonger dans une zone active du calorimetre (detecteur de muons), comme pour un candidat d'electron (muon). Les candidats de ISOTRK recuperent de vrais leptons charges qui seraient autrement perdus dans les zones non instrumentees du detecteur. L'ajout de la categorie ISOTRK a la categorie TIGHT permet de reconstruire plusieurs bosons W reels et par la suite de recuperer plusieurs evenements WH, ce qui ameliore la sensitivite de la recherche de WH.Comme a CDF il n'y a pas de declencheurs dedies au leptons charges ISOTRK, on utilise pour la categorie ISOTRK trois declencheurs bases sur MET et jets avec une nouvelle methode qui permet de maximiser le nombre d'evenements accumules tout en evitant les correlations des declencheurs. Pour chaque evenement, ce n'est que le declencheur avec la plus grande efficacite qui est utilise. Le nombre d'evenements ramasses est legerement inferieur a celui d'un "OR" logique entre les declencheurs, mais cela est compense par une erreur systematique qui est a la fois moins importante et plus facile a evaluer. Dans sa forme la plus generale, la methode peut etre utilisee par toute analyse qui utilise un nombre variable de declencheurs differents. L'utilisation de la categorie ISOTRK en plus de la categorie TIGHT augmente de 33% le nombre d'evenements WH selectionnes et decroit de 15.5% a 19.0% la limite superieure mediane attendue. La limite superieure observee (attendue) varie entre 2.39 x SM(2.73 x SM) pour un boson de Higgs de 100 GeV/c^2 jusqu'a 31.1 x SM(31.2 x SM) pour un boson de Higgs de 150 GeV/c^2. En meme temps, pour un boson de Higgs de 115 GeV/c^2, la valeur est 5.08 x SM(3.79 x SM).
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Leveque, Jessica. „Recherche d'un boson de Higgs leger produit en association avec une paire de quarks top dans l'experience ATLAS“. Phd thesis, Université de la Méditerranée - Aix-Marseille II, 2003. http://tel.archives-ouvertes.fr/tel-00003738.
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L'un des principaux objectifs de l'experience ATLAS est la recherche de la derniere particule manquante du modele standard, le boson de Higgs, et l'etude de ses proprietes. Cette experience sera placee aupres du futur collisionneur de protons LHC, dont le demarrage est prevu pour l'annee 2007 au CERN. Les travaux presentes dans cette these sont dedies a la recherche d'un boson de Higgs de masse inferieure a 200 GeV/c2, dans le canal de production associee pp->ttH. L'identification des jets contenant des hadrons beaux est fondamentale pour l'etude du boson de Higgs et du quark top. Les performances d'etiquetage des jets b sont etudiees en details dans le canal ttH, H->bb, et pour des conditions de fonctionnement tres proches de celles attendues au demarrage des prises de donnees, (detecteur a pixels incomplet, bruit d'empilement et inefficacites de detection). Pour une efficacite d'identifcation de jets b de 60%, les taux de rejet attendus sont de 80% pour les jets legers et 7% pour les jets c. Si la decouverte du boson de Higgs dans ATLAS semble relativement aisee, la mesure de ses parametres, et en particulier la determination des couplages aux differents fermions, est beaucoup plus delicate. Une etude de faisabilite est proposee pour un nouveau canal, ttH, H->WW(*). Ce canal est le seul qui permet une determination directe du couplage de Yukawa du quark top dans l'intervalle de masse 130-200 GeV/c2. Pour un boson de Higgs de 160 GeV/c2, la precision statistique attendue apres trois annees de prise de donnees a haute luminosite est de 7 %.
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Raine, John. „Evidence for the production of a Higgs boson in association with two top quarks with the ATLAS detector“. Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/evidence-for-the-production-of-a-higgs-boson-in-association-with-two-top-quarks-with-the-atlas-detector(8c0c9d01-ee21-4f7e-9db6-1f5d92de1faf).html.
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In this thesis, the search for the production of the Higgs boson in associationwith two top quarks is presented. The main focus of this work is on the analysis optimised for the decay of the Higgs boson to a b-quark pair. The analysis is performed using 36.1 fbâ1 of ppcollision data at a centre of mass energy sqrt(s)=13 TeV collected by the ATLAS detector at the Large Hadron Collider during 2015 and 2016. The signal strength of ttH in relation to the Standard Model prediction for a Higgs boson with a mass of 125 GeV is measured to be mu(ttH) = 0.87 +0.64â0.61, with signal strengths greater than 2.0 excluded at the 95% confidence level. The combination of this analysis with searches targeting additional Higgs boson decay modes is subsequently presented. The measured signal strength in relation to the Standard Model prediction is mu(ttH) = 1.2 +/-0.3. This correspondsto an observed (expected) significance for ttH of 4.2sigma (3.8sigma), constituting evidence for the ttH production mode. Finally, a study into the ability to observe and model the colour connection of b-quarks in ttH(bb) and ttbar+jets events is presented. The jet pull angle observable is used to investigate the effect of colour connection on jet substructure. Such an observable is found to be sensitive to the underlying colour structure in events, showing differences between b-quarks which decay from a colour singlet in comparison to a colour octet. However, the effect is found to be small and a larger dataset is required to measure the effect in ttH events.
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Chen, Xuan. „Hadronic production of a Higgs Boson in association with a jet at next-to-next-to-leading order“. Thesis, Durham University, 2015. http://etheses.dur.ac.uk/11158/.
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In this thesis the production of a Higgs boson in association with a hadronic jet at the Large Hadron Collider is studied using the effective interaction between the Higgs boson to gluons induced by a heavy quark. The Leading Order (LO), Next- to-Leading Order (NLO) and Next-to-Next-to-Leading Order (NNLO) perturbative QCD corrections are studied for all of the parton channels. The infrared (IR) diver- gent behaviour of the various contributions to the partonic cross section is regulated using the antenna subtraction formalism. This method has previously been used at NNLO in the calculation of three jets production in the e+e− annihilation and for the gluonic dijet production via proton collision. The research presented in this thesis extends the antenna formalism to include scattering processes in which the initial state parton changes its identity. All contributions to the pp → H+jet pro- cesses are calculated at LO, NLO and NNLO and numerically tested to demonstrate the convergence between the matrix elements and the antenna subtraction terms in the various unresolved limits. As an example of the phenomenological impact of this work, numerical results for the total and differential Higgs plus one jet cross sections are presented for the purely gluonic subprocesses.
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Levêque, Jessica. „Recherche d'un boson de Higgs léger produit en association avec une paire de quarks top dans l'expérience ATLAS“. Aix-Marseille 2, 2003. http://www.theses.fr/2003AIX22024.
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Psoroulas, Serena [Verfasser]. „Measurement of jets production in association with a Z boson and in the search for the SM Higgs boson via H →ττ→ll+4ν with ATLAS / Serena Psoroulas“. Bonn : Universitäts- und Landesbibliothek Bonn, 2013. http://d-nb.info/1045276391/34.
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Ravenscroft, Thomas Oliver. „Studies of possible improvements to the b-Jet energy resolution applied to the search for the Higgs boson produced in association with a W boson at the ATLAS detector“. Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6664/.
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This thesis presents a measurement of the cross-section for the produc- tion of a Higgs boson in association with a W boson. Where the Higgs boson decays to a pair of b-quarks and the W boson decays leptonically to a electron-neutrino pair or muon-neutrino pair. The measurements have been taken using 20 fb−1 of data collected at a centre-of-mass energy √s = 8 TeV from the ATLAS detector; one of the four main experiments at the Large Hadron Collider (LHC). An expected upper limit is calculated in the background-only hypothesis at 1.51 times the Standard Model expectation. The signal strength is measured at a Higgs boson mass m = 125 GeV to be μ = 3.22+0.71(stat.)+1.03(syst.) H −0.69 −0.87 As part of the analysis performed, extensive studies have been carried out into the impact of the four jet calibrations used by the WH → lνb ̄b analysis for the Run I result. Jet calibrations are used to correct for detector effects and inefficiencies in the reconstruction of the jets. In addition to the studies on the current jet calibration methods, two additional jet calibrations are studied and their perfor- mance within the analysis are measured, with comparisons against the nominal expected upper limit. The first additional calibration replaces the current jet pT calibration with one which uses different calibrations depending upon whether the jet contains a muon or not. By applying this calibration the expected upper limit improves to 1.50 times the Standard Model expectation. The second calibration uses a regression to improve the b-jet resolu- tion. Using well modelled variables, there is no change in the expected upper limit, however by considering all variables, the expected upper limit improves to 1.47 times the Standard Model expectation, giving a 2.5% improvement to the nominal analysis.
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Baca, Matthew. „Search for production of dark matter in association with a Higgs boson decaying to bb with the ATLAS detector“. Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8450/.
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Using 3.2 fb^-1 of sqrt(s) =13TeV proton-proton data collected in 2015 with the ATLAS detector at the Large Hadron Collider, new limits were imposed on the associated production of Dark Matter with a 125GeV Higgs boson which decays into a pair of b-quarks. The final state of the signal is a pair of b-quark jets and large Missing Transverse Momentum attributed to the DM escaping the detector. The dominant backgrounds were simulated. These were subject to selection requirements to increase signal to background ratio. Three regions were designated based on the number of leptons in the event. 0 lepton events made up the signal region. Events with 1 and 2 leptons were control regions. Similar selection requirements were applied to the control regions as in the signal region, in order to examine a similar phase space. A blinding region was established in the 0 lepton region over the mbb distribution to mask where a reconstructed 125GeV Higgs boson would appear. The control regions and the side bands in the signal region were then fit to the mbb data distribution. Unblinding of the signal region did not result in the discovery of the decay channel, but allowed limits to be imposed.
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Delabat, Díaz Yasiel. „Search for Standard Model Higgs bosons produced in association with top-quark pairs in ttH multilepton final states using the ATLAS detector at the LHC“. Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/22550.
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Diese Arbeit beschreibt die Suche nach assoziierter Produktion eines Higgsbosons und eines Top-Quark Paares in Proton-Proton Kollisionen bei einer Schwerpunktsenergie von 13 TeV. Für diese Analyse wurden Ereignisse analysiert, die exakt zwei Leptonen mit gleichem Ladungsvorzeichen oder exakt drei Leptonen enthalten und daher auf die Higgs Zerfallsmoden in H->WW, H->ZZ und H->tautau sensitiv sind. Die Daten wurden mit dem ATLAS Detektor am Large Hadron Collider (LHC) in den Jahren 2015-17 aufgezeichnet. Der grösste Untergrund in beiden Kanälen stammt aus assoziierter Produktion von Vektorbosonen mit einem Top-Quark Paar (ttW und tt(Z/gamma)), Dibosonproduktion und Ereignisse, die Photonen und Hadronen, die fehlerhaft als Leptonen identifiziert wurden, erhalten oder Leptonen, die aus Zerfällen von Hadronen stammen. Der Leptonuntergrund wurde mit einer neuen Methode abgeschätzt, die auf separaten Kategorien für jeden Produktionsmodus des Leptonuntergrundes basiert. Der Beitrag jeder Kategorie wird in verschiedenen Kontrollregionen aus dem Vergleich von Daten mit der Simulation bestimmt. Das Verhältnis des gemessenen ttH Wirkungsquerschnitts zu der Vorhersage des Standardmodells und die Normierungsfaktoren des Untergrundes werden gleichzeitig in einem Profile-Likelihood-Fit bestimmt. Das Verhältnis des gemessenen zum erwarteten ttH Wirkungsquerschnitts, unter der Annahme einer Higgsbosonmasse von 125 GeV, wurde zu 0.88(+0.54/-0.51) mit einer beobachteten (erwarteten) Signifikanz von 1.80 (2.52) Standardabweichungen gemessen. Das entspricht einem geschätzten Wirkungsquerschnitt für die ttH Produktion von 446(+241/-227) fb, in Übereinstimmung mit der Standardmodellvorhersage von 507(+35/-50) fb.This thesis describes the search for the associated production of a Higgs boson and a top-quark pair in proton-proton collisions with a center-of-mass energy of 13 TeV. The analysis focuses on events containing two leptons with same-sing electric charge or exactly three leptons in the final state. With these requirements, the analysis is sensitive to the H->WW, H->ZZ and H->tautau Higgs decay modes. The used data was recorded with the ATLAS detector at the Large Hadron Collider (LHC) during the 2015-17 period. The primary sources of background were found to be ttW, tt(Z/gamma), Diboson processes and events containing fake or non-prompt leptons coming from hadron decays, photon conversions and electron charge mis-identification. The estimation of the hadron decay and photon conversion fake backgrounds was performed using a novel semi-data driven technique where Monte Carlo background categories are created for each fake process of interest. A profile likelihood fit to data is then used to extract a normalization factor for each fake category, which are used to correct the Monte Carlo predictions. The ratio of the measured ttH signal cross-section to the Standard Model expectations and a normalization factor for the ttW process are extracted simultaneously from the same fit. The measured to expected cross-section ratio for a Standard Model Higgs boson of mass 125 GeV was found to be 0.88(+0.54/-0.51) with an observed (expected) significance of 1.80 (2.52) standard deviations. This corresponds to an estimated ttH cross-section of 446(+241/-227) fb, in agreement with the Standard Model prediction of 507(+35/-50) fb.
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Noguchi, Yohei. „Measurement of Higgs boson properties using the decay channel to b-quarks following associated production with a vector boson in pp collisions at √s=13 TeV“. Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263460.
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Heer, Sebastian [Verfasser]. „Top-quark pair production in association with a Z boson in the final state with four charged leptons / Sebastian Heer“. Bonn : Universitäts- und Landesbibliothek Bonn, 2019. http://d-nb.info/1200019903/34.
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Kövesárki, Peter [Verfasser]. „Multivariate methods and the search for single top-quark production in association with a W boson in ATLAS / Peter Kövesárki“. Bonn : Universitäts- und Landesbibliothek Bonn, 2013. http://d-nb.info/1044970855/34.
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Nechansky, Filip. „Search for the production of a Higgs boson decaying into a pair of bottom quarks in association with a pair of top quarks at 13 TeV with the ATLAS detector“. Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/23027.
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Die Entdeckung des Higgs-Bosons im Jahr 2012 bestätigt das Standardmodell als die erfolgreichste Theorie, die die grundlegenden Wechselwirkungen von Elementarteilchen beschreibt. Eine der wichtigen Eigenschaften des Higgs-Bosons ist seine Yukawa-Kopplung an das Top-Quark, die aufgrund der hohen Masse des Quarks im Standardmodell am stärksten ist.
Diese Arbeit berichtet über eine Messung der Top-Yukawa-Kopplung mit Daten, die vom ATLAS-Detektor von 2015 bis 2018 bei einem Massenschwerpunkt von 13 TeV aufgezeichnet wurden. Die Kopplung wird in ttH(bb)-Ereignissen untersucht, einem Endzustand, der die Zerfälls-produkte von zwei Top-Quarks enthält und in dem zusätzlich ein Higgs-Boson emittiert wird, welches in Bottom-Quark-Paar zerfällt. Dieser Zerfallskanal des Higgs-Bosons hat das größte Verzweigungsverhältnis, wird jedoch durch die Beschreibung des dominanten Untergrundprozesses ttbb, ein Top-Quark-Paar mit zwei zusätzlichen b-Quarks im Endzustand systematisch beschränkt.
Die Messung nutzt die Fähigkeit des ATLAS-Detektors, Jets von einem b-Quark zu identifizieren, um Analysebereiche mit verschiedenen Zusammensetzungen von Signal und Untergrund zu konstruieren. Um das Signal weiter zu separieren, wird eine Reihe von multivariaten Algorithmen verwendet und der ttH-Prozess wird unter Verwendung eines Profile-Likelihood-Fits extrahiert.
Die Ergebnisse werden für den Kanal mit einem einzelnen Lepton im Endzustand und für eine Kombination mit dem Dilepton-Kanal gezeigt. Die Untergrundgenauigkeit wird im Detail untersucht, wobei große Fehlmodellierungen festgestellt werden. Das gemessene Verhältnis der ttH-Produktion zur Standardmodell-Vorhersage beträgt mu(ttH) = 0,84+0,45- 0,39 (syst.) +-0,21 (stat.). Das Ergebnis stimmt mit der Vorhersage des Standardmodells überein und entspricht einer beobachteten (erwarteten) Signifikanz von 1,9 sigma (2,3 sigma), eine Verbesserung gegenüber der vorherigen ATLAS-Messung, bei der eine Signifikanz von 1,4sigma (1,6 sigma) ermittelt wurden.The discovery of the Higgs Boson in 2012 confirms the Standard Model as the most successful theory describing the fundamental interactions of elemental particles. One of the important properties of the Higgs boson is its Yukawa coupling to the top quark, which in the Standard Model is the strongest due to the high mass of the quark. This thesis reports on a measurement of the top-Yukawa coupling with data collected by the ATLAS detector from 2015 to 2018 at 13 TeV center of mass energy. The coupling is studied in ttH(bb) events, a final state containing decay products of two top quarks with additional emission of a Higgs boson, where the Higgs decays into a pair of bottom quarks. This decay channel of the Higgs Boson has the largest branching ratio, but is systematically limited by the description of the dominant background process ttbb, a tt with additional two b quarks in the final state. The measurement takes advantage of the ability of the ATLAS detector to identify jets coming from a b quarks to construct analysis regions with various compositions of the signal and the background. To further separate the signal, a series of multivariate algorithms is employed and the ttH process is then extracted using a profile likelihood fit. The results are shown for the channel with a single lepton in the final state and for a combination with the dilepton channel. The background performance is studied in detail, where large mis-modeling is found. The measured ratio of the ttH production compared to the Standard Model prediction is found to be mu(ttH) = 0.84 +0.45 -0.39 (syst.) +-0.21 (stat.). The result is in agreement with the Standard Model prediction and corresponds to an observed (expected) significance of 1.9 sigma (2.3 sigma), an improvement compared to the previous ATLAS measurement which reported 1.4 sigma (1.6 sigma).
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Giorgi, Francesco Michelangelo. „Measurement of the Production Cross-Section of Single Top Quarks in Association with W Bosons at ATLAS“. Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/18060.
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Das Ziel der vorgelegten Arbeit ist die Messung des Wirkungsquerschnittes der elektroschwach vermittelten Produktion einzelner Top Quarks in Assoziation mit einem W-Boson. Dieser Prozess wird auch abkürzend als Wt-Kanal bezeichnet. Die Vermessung dieses Produktionskanals stellt einen Test der Standardmodell-Vorhersage dar und bietet gleichzeitig die Möglichkeit durch einen Vergleich mit anderen Produktionskanälen für einzelne Top Quarks (t- und s-Kanal) Rückschlüsse auf neue Physik jenseits des Standardmodells zu ziehen. Nach einer allgemeinen Einführung zur Physik des Top Quarks folgt eine Beschreibung der für die Detektion und Rekonstruktion physikalischer Objekte wichtigen Systeme des ATLAS-Detektors.Anschlie{\ss}end wird die Analyse der Proton-Proton-Kollisions Daten die im Jahr 2011 vom ATLAS Detektor am Large Hadron Collider (LHC) augzeichnet wurden präsentiert.Diese Daten wurden bei einer Schwerpunktsenergie von 7 TeV aufgezeichnet und haben einen Umfang von 4.7 inverse femtobarn.Da die Produktionsrate des Wt-Kanals am LHC sehr klein im Vergleich zu seinem Hauptuntergrund ist, wurde ein Chi-Quadrat-basierter kinematischer Fit entwickelt um die Identifikation der Signalereignisse zu begünstigen. Hierbei werden W-Boson und Top-Quark aus den Endzustandsteilchen rekonstruiert und durch Bedingungen
hinsichtlich der W-Boson und Top Quark Masse evaluiert. Der errechnete Chi-Quadrat-Wert gibt die Wahrscheinlichkeit an, mit der das einzelne Ereignis mit der Signal-Hypothese übereinstimmt und kann als Schnittvariable verwendet werden um eine striktere Ereignisselektion zu erhalten. Die Messung ist von systematischen Unsicherheiten dominiert, die fast 100 % des gemessenen Wirkungsquerschnitts betragen.The work reported in this thesis is aimed at measuring the cross section of electroweak single top quark production in association with a W boson, a process also referred to as Wt-channel. The interest in this production mechanism relies in the confirmation of the Standard Model predictions together with the possibility of identifying new physics phenomena when comparing its cross section with the one of the other single top production modes (the t- and s-channel.) After providing a general introduction on the physics of the top quark and a description of the experimental setup employed for the detection and the reconstruction of the physics objects, the analysis of 4.7 femtobarn of proton-proton collision data at a centre-of-mass energy of 7 TeV, recorded by the ATLAS detector at the Large Hadron Collider in the year 2011, is presentedSince the Wt channel production rate at the LHC is considerably smaller than its main background, a chi-squared based kinematic fit has been developed to help the identification of the signal events allowing the use of simultaneous mass constraints from the W boson and the top quark populating the final states. The chi-squared value in each event is then used as a parameter to rank the event in terms of its probability to match or not the signal hypothesis and a cut on its value is used to implement a first tight event selection. The final selection step consists of requiring that the system composed by the top quark and the W boson reconstructed by the fit is balanced in the transverse plane. The measurement is found to be dominated by the systematic uncertainties which affect it by an amount close to 100% of the cross section value.
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Smith, Geoffrey N. „A Search For the Standard Model Higgs Boson Produced in Association with Top Quarks in the Lepton + Jets Channel at CMS“. The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397747965.
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Vittori, Camilla <1990>. „Inclusive Z boson production and in association with b-jets in proton-proton collisions at 13 TeV with the ATLAS experiment“. Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amsdottorato.unibo.it/8604/1/tesi.pdf.
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In this thesis, the measurement of the inclusive Z-boson production cross section at the centre of mass energy of √s =13 TeV is first presented. The data analysed were collected by ATLAS during early Run 2 of LHC and correspond to a luminosity of 81 pb−1. The cross section measurement is performed separately in the electron and muon decay channels and in their combination. The ratio with respect to the W cross section is also performed in the same fiducial phase space, and it benefits from cancellation of some experimental uncertainties. Results are compared to NNLO calculations in perturbative QCD.
The Z boson is then studied in associated production with at least one and at least two b-jets, using an enlarged dataset (36 fb−1) collected by ATLAS at the centre of mass energy of √s =13 TeV. Integrated cross sections are measured at the particle level for both the electron and muon decay chan- nels. Differential cross sections are measured as a function of the leading b-jet transverse momentum and rapidity, the Z boson rapidity and the an- gular separation between the Z boson and the b-jet. For events containing two b-jets at particle level, the cross section is measured as a function of the invariant mass and angular separation of the two highest transverse mo- mentum b-jets, and as a function of the kinematics of the sub-leading b-jet. Results are compared to LO and NLO Monte Carlo predictions.
Finally, I present the work performed on the LUCID detector, the official ATLAS luminometer, to analyse calibration data with a 207Bi source, and the activity within the ATLAS muon performance group, to evaluate the muon reconstruction scale factors, using data acquired in Run 2.In questa tesi, è presentata la misura della sezione d’urto di produzione inclusiva del bosone Z all’energia del centro di massa di √s =13 TeV. I dati analizzati sono stati raccolti da ATLAS all’inizio del Run 2 di LHC e corrispondono ad una luminosità di 81 pb−1. La sezione d’urto è misurata separatemente nei canali di decadimento elettronico e muonico e successiva- mente nella loro combinazione. Il rapporto tra le sezioni d’urto dei bosoni Z e W è misurato nello stesso volume fiduciale e benificia della cancellazione di alcune incertezze sperimentali. I risultati sono confrontati con calcoli teorici disponibili al NNLO in QCD perturbativa. Inoltre, è presentata anche la misura della produzione del bosone Z in asso- ciazione ad almeno uno e almeno due b-jets, usando dati raccolti da ATLAS all’energia del centro di massa di √s =13 TeV. Le sezioni d’urto integrate sono misurate al particle level per i canali elettronico e muonico. Le sezioni d’urto differenziali sono misurate in funzione del momento trasverso e della rapidità del b-jet più energetico, della rapidità del bosone Z e di una serie di variabili angolari tra il bosone Z e il b-jet. Per gli eventi con due b-jets al particle level, la sezione d’urto è misurata in funzione della massa invariante e delle separazioni angolari tra i due b-jets più energetici e delle variabili cinematiche del secondo b-jet più energetico. I risultati sono confrontati con predizioni Monte Carlo al LO e NLO. Infine, sono presentati i lavori dedicati all’analisi dei dati di calibrazione del rivelatore LUCID, il luminometro ufficiale di ATLAS, e alla determinazione delle efficienze di ricostruzione dei muoni, all’interno del gruppo di perfor- mance, usando i dati acquisiti nel Run 2.
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Radloff, Peter. „Search for new light scalar bosons produced in association with a bottom-quark and decaying to two tau leptons“. Thesis, University of Oregon, 2016. http://hdl.handle.net/1794/20536.
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A search for new neutral scalar bosons produced in association with a bottom-quark is performed. The analysis uses data acquired with proton-proton collisions at a center-of-mass energy of 8 TeV and observed with the ATLAS detector at the LHC, corresponding to 20.3 $fb^{-1}$ of integrated luminosity. The search focuses on scalar boson decays into tau lepton pairs, where each decays leptonically ($\tau \rightarrow l \nu_{\tau} \bar{\nu_{l}}$) resulting in one muon, one electron and four neutrinos. No significant excess is observed and upper limits on the signal strength are determined as a function of scalar boson mass.
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Matić, Andrea [Verfasser], und Jeanette [Akademischer Betreuer] Lorenz. „Search for Dark Matter in association with a Higgs boson decaying into b-quarks with the ATLAS detector / Andrea Matić ; Betreuer: Jeanette Lorenz“. München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2020. http://d-nb.info/122784011X/34.
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