Dissertations / Theses on the topic 'Associated Bottom Higgs Production'
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Dovier, Giacomo Oliviero. "Semi-inclusive associated bottom-Higgs production at LHC: the complete one-loop electroweak in the MSSM." Doctoral thesis, Università degli studi di Trieste, 2011. http://hdl.handle.net/10077/4815.
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2009/2010Il bosone di Higgs il tassello mancante del Modello Standard: predetto da Peter Higgs negli anni sessanta, non ancora stato osservato sperimental- mente. Il Large Hadron Collider stato costruito con questo obiettivo in mente, assieme a molti altri. Uno dei processi pi interessanti per la pro- duzione di Higgs Supersimmetrico bg -> bH0 ( A0, h0). La natura dell'accoppiamento Yukawa nel MSSM lo rende predominate per alti valori di tan(beta) . In questa tesi vengono calcolate le correzioni elettrodeboli ad un loop alla sezione d'urto del processo nel MSSM, e viene mostrato come esse possano essere molto rilevanti per alcune regioni dello spazio dei parametri. Viene anche mostrato come i risultati siano indipendenti dalla scelta dello schema di rinormalizzazione tra DCPR and DR, ed anche come la consueta Improved Born Approximation non riproduca accuratamente i risultati ad un loop, mentre una diversa possibile approssimazione, la Reduced Vertex Approximation, in migliore accordo con il calcolo completo. Viene quindi eff ettuato un confronto con i risultati per un Two Higgs Doublet Modle, e viene mostrato come la di erenza con i risultati nel MSSM sia rilevante ad un loop, rendendo lo studio di questo processo una possibile via per discriminare tra i due modelli.
The Higgs particle is the missing piece of the Standard Model picture: pre- dicted by Peter Higgs in the late sixties, it has yet to be observed in a collider. The Large Hadron Collider has been built with this goal in mind, among many others. A very important channel to look at for SUSY Higgs production is bg -> bH0 (A0, h0). The nature of the MSSM Yukawa couplings make it dominant for high Values of tan(beta) . In my work I calculate the electroweak one loop corrections to the cross section of the process' cross section in the MSSM, and show that they can be very relevant for some regions of the parameters' space. It is also shown how the results obey a nice scheme independence at one loop for the two renormalization schemes DCPR and DR, as well as how the usual Improved Born Approximation fails in this case to reproduce the one loop results accurately, while a di fferent suggested Reduced Vertex Approximation is in better agreement with the full calculation. I then proceed to make a comparison with the results for a Two Higgs Doublets Model, and show that the di fference with the MSSM are big at the one loop level, such that this process could provide a way to discriminate between the two models.
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Lund, Gustav. "Associated charged Higgs boson and squark production in the NUHM model." Thesis, Uppsala University, High Energy Physics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-114395.
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Conventional searches for the charged Higgs boson using its production in association with Standard Model (SM) quarks is notoriously weak in the mid-tanB range. Hoping to find an alternate channel to fill this gap, the production of the charged Higgs boson in association with supersymmetric squarks is studied. Using Monte Carlo generators the production at the LHC is simulated within the non universal Higgs mass model (NUHM). If the six parameters of the model (m0, m1/2, A0, tanB, u, mA) induce small masses of the stop, sbottom and charged Higgs, the production cross section can be of the order pb. Through scans of the input parameter the cross section is maximized, with the requirement that the stop decays directly to a neutralino - simplifying detection, in the point (m0, m1/2, A0, tanB, u, mA) = (190, 187, -1147, 179, 745, 13.2) where the cross section is 559 fb.
The production is compared to the irreducible backgrounds stop, stop, t, tbar and t, tbar + 2 jets. The former poses no severe constraints and can be easily removed using appropriate cuts. The latter, SM background, has a cross section almost 1000 times larger and strong cuts must be imposed to suppress it. Neglecting hadronization and systematic effects, we show that a 5 sigma discovery is possible at 133 fb-1. In this range, mH+ = 194 GeV and tanB = 13.2, other channels have little or no prospects of detecting the charged Higgs and the studied process shows good prospects for complementing charged Higgs searches at the LHC in the mid-tanB range.
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Agaras, Merve Nazlim. "Searches for associated Higgs Boson production with top quark pair and Higgs pair production in multi lepton final states with the ATLAS detector." Thesis, Université Clermont Auvergne (2017-2020), 2020. http://www.theses.fr/2020CLFAC023.
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Depuis la découverte du boson de Higgs à une masse d'environ 125 GeV par les deux collaborations ATLAS et CMS en juillet 2012, il est devenu crucial de mesurer ses propriétés, telles que ses couplages avec d'autres particules, et de rechercher tout écart par rapport aux prévisions du Modèle Standard (SM). Le couplage Yukawa du quark top est proche de l'unité et est le plus fort dans le secteur fermionique. Par conséquent, ce couplage joue un rôle crucial dans la théorie. La détermination de la production de boson de Higgs avec une paire de quarks top (ttH) offre un accès a l'ordre dominant pour mesurer ce couplage. L'analyse de la production de ttH dans le cadre de l'expérience ATLAS exploite plusieurs canaux de désintégration du Higgs, ainsi que différents modes de désintégration des quarks top. Dans cette thèse, l'étude du processus ttH (H → Multi lepton) est présentée dans la topologie où le Higgs se désintègre en WW,ZZ ou tautau, en utilisant un ensemble de données correspondant à une luminosité intégrée de 79,8fb^-1 à √s = 13 TeV, recueillies avec le détecteur ATLAS entre 2015 et 2017. L'amélioration des connaissances sur la modélisation des bruits de fond et un modèle d'ajustement complexe est utilisée avec de nombreux degrés de liberté. Des ajustements particulièrement différents sont présentés afin de comprendre la modélisation du principal bruit de fond irréductible, ttW. En outre, une recherche sur la production de paires de bosons de Higgs dans les états finaux multi leptoniques est présentée. La recherche utilise 139fb^-1 de données issues de collisions proton-proton à une énergie de centre de masse de 13 TeV fournies par le Grand collisionneur de hadrons (LHC) et enregistrées par l'expérience ATLAS entre 2015 et 2018. Les premières études du canal 2 leptons de même signe sont réalisées afin d'optimiser le point de fonctionnement des leptons et d'estimer les contributions des bruits de fond. La méthode d'ajustement du modèle est appliquée pour estimer les bruits de fond réductibles et calculer la limite supérieure préliminaire prévueSince the discovery of the Higgs boson at a mass around 125 GeV by both ATLAS and CMS collaborations in July 2012, it became crucial to measure its properties, such as its couplings to other particles, and search for any deviations from the Standard Model (SM) predictions. The top quark Yukawa coupling is close to unity and the strongest in the fermionic sector. Therefore, this coupling plays a crucial role in the theory. Determination of the associated production of The Higgs boson production with a pair of top quarks (ttH) offers a tree-level access to measuring this coupling. The analysis of ttH production at ATLAS experiment exploits several Higgs decay channel, together with different top quark decay modes. In this thesis, the study of the ttH (H → Multi lepton) process is presented in the topology where the Higgs decays to WW,ZZ or tautau, using a dataset corresponding to an integrated luminosity of 79.8fb^-1 at √s = 13 TeV, collected with the ATLAS detector between 2015-2017. Improved knowledge on the background modelling and the complex fit model is used with many degrees of freedoms. Particularly different fit setups are presented in order to understand the modelling of the major irreducible background, ttW. Furthermore, a search for the SM Higgs boson pair production in the multi lepton final states is presented. The search uses 139fb^-1 of proton-proton collisions data at a centre-of-mass energy of 13 TeV provided by the Large Hadron Collider (LHC) and recorded by the ATLAS experiment in 2015 and 2018. The first studies in two lepton same-sign channel is performed for lepton working point optimisation and estimation of background contributions. Template fit method is applied to estimated the reducible backgrounds and preliminary expected upper limit is calculated
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Agnew, James Paul. "Search for the associated production of Higgs boson with top anti-top pairs." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/search-for-the-associated-production-of-higgs-boson-with-top-antitop-pairs(c24f5919-6f3f-4b13-ad72-9ef9efbcb6bb).html.
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This thesis describes the search for the associated production of a Higgs boson with top anti-top pairs in proton anti-proton collisions at a centre-of-mass energy of 1.96 TeV.The data used were collected by the D0 detector during the RunII data taking period which ran from 2001 to 2011 at the Tevatron Collider located at the Fermi National Accelerator Laboratory (or Fermilab).Distributions of the H_T variable separated into 3 jet, 4 b-tagging and 2 lepton categories were used as inputs to a modified frequentist limit setting procedure, which was in turn used to search for the ttH process with Higgs decaying to b anti-b pairs. Since this process was not observed, limits were set on the cross section times branching ratio, with an expected (observed) limit of 36.8 (65.8) measured for a Higgs mass value of 125 GeV.
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Black, Curtis William. "Search for the Higgs boson decaying to tau leptons in the associated production mode at ATLAS." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/15432.
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This thesis presents the results of the search for the Standard Model Higgs boson, decaying to tau leptons, and produced in association with a leptonically decaying vector boson. Using the ATLAS detector at the LHC, the analysis is performed on 20.3 inverse femtobarn of proton-proton collisions recorded in 2012 at 8 TeV centre-of-mass energy. The analysis is made robust through the development of a background estimation method which uses Monte-Carlo simulation for the irreducible backgrounds and a data-driven estimation for the reducible backgrounds. No significant excess of events is observed. For a Higgs boson mass of 125 GeV, the 95% confidence level upper limit on the observed cross-section is 5.6 times the Standard Model prediction. The measured signal strength, normalized to the Standard Model expectation, is 2.3±1.6. This excess corresponds to a 1.4σ upward fluctuation of the background-only expectation but is consistent with the Standard Model expectation.
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CIRIOLO, VINCENZO. "Study of the Higgs boson associated production with a vector boson in the Higgs boson diphoton decay channel with the CMS detector." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2019. http://hdl.handle.net/10281/241085.
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Questa tesi di dottorato presenta lo studio della produzione associata di un bosone di Higgs con un bosone vettore (VH) in collisioni protone-protone, utilizzando i dati raccolti ad un'energia nel centro di massa delle collisioni pari a 13 TeV con l'esperimento CMS nel 2016. Questo studio è ristretto allo stato finale dove il boson di Higgs decade in due fotoni.
Dopo un'introduzione riguardante il contesto teorico e sperimentale che motiva questo studio (Capitolo 1) e una descrizione generale dell'esperimento CMS (Capitolo 2), il lavoro sperimental necessario per ottenere exxellenti performance dal calorimetro eletromagnetico di CMS sono descritti in dettaglio (Capitolo 4). Le utilizzate nell'analisi dei dati e i risultati sono descritti nel capitolo 4, includendo la discussione dell'ottimizzazione dell'analisi che sono stati ritenuti benefici per gli sviluppi futuri. In particolare, il canale in cui il bosone vettore decade in due quark a quello in cui il bosone W decade leptonicamente sono descritti. I risultati dell'analisi sono inclusi in un articolo recentemente sottomesso per la pubblicazione su una rivista internazionale, rappresentando i primi risultati della misura della produzione VH nel canale H→ γγ con dati raccolti nel Run 2 di LHC.This Ph.D. thesis presents a study of the associated production of the Higgs boson with a vector boson (VH) in proton-proton collisions, using data collected at a center-of-mass energy of 13 TeV with the CMS experiment in 2016 for an integrated luminosity of 35.9 fb −1 . The study is restricted to final states were the Higgs boson decays in two photons (H→ γγ). After an introduction on the experimental and theoretical landscape that motivates this study (Chapter 1) and an overview of the CMS experiment (Chapter 2), the exper- imental work performed to ensure the best quality of the CMS ECAL reconstruction is described in detail (Chapter 3). The analysis method and the results are then described (Chapter 4), including the discussion of optimization steps that were identified and will be relevant for future developments. In particular, the channels with the vector boson decaying into a pair of quarks and the W boson decaying into a lepton and a neutrino are described This analysis, included in a paper recently submitted for publication, represents the first result on the measurement of the VH production process in the H→ γγ final state with the LHC Run 2 data.
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Howard, Jacob Russell. "Measurements of the Higgs Boson in the H-ττ decay channel." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:14e6e708-0cd6-4022-a4b2-343c18c8e260.
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The generation of vector boson mass via the Higgs mechanism in the Standard Model has been confirmed by the 2012 discovery of a candidate Higgs boson in the H→WW, H→ZZ, and H→γγ decay channels. In contrast, the Yukawa couplings hypothesized to provide the mass of fermions in the Standard Model have yet to be observed. The H→ττ decay channel currently provides the best opportunity for observing these couplings. This thesis describes two separate but related searches for Higgs boson decays in the H→ττ decay channel using proton-proton collisions recorded by the ATLAS detector. The first analysis is a general search for all Higgs boson production mechanisms leading to a H→ττ decay using 4.5 fb−1 of 7 TeV and 20.3 fb−1 of 8 TeV proton-proton collision data. A deviation from the background-only hypothesis is observed with a significance of 4.5σ for a hypothetical Higgs boson mass of mH = 125 GeV — a strong indication of a H→ττ signal. For the same mass point, the best fit value for the signal strength is found to be 1.43 +0.43−0.37 x the Standard Model expectation. The second analysis is a search for Higgs boson production in association with a vector boson using 20.3 fb−1 of 8 TeV proton-proton collision data. Results in the ZllH→τlτh channel indicate limits of 9.14 x the Standard Model expectation for VH signal production at mH = 125 GeV. In addition, two studies on enhancement of computing performance in the ATLAS trigger and data analysis pipeline are presented.
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Walser, Manuel. "NLO QCD and SUSY-QCD corrections to associated MSSM Higgs production with heavy quarks at hadron colliders /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17592.
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Asquith, L. "Using ATLAS to investigate the associated production of a Higgs Boson with a pair of top quarks." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/20202/.
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This thesis describes the study of the channel t \overline{t} H^{0}(H^{0}\rightarrowb\overline{b} with the ATLAS detector with 30fb^-1 of data and a center of mass energy of 10 TeV. Chapter 1 provides a description of the ATLAS detector, followed by a theoretical background in Chapter 2 and a discussion of phenomenology and event generation in Chapter 3. Issues associated with leptons and missing energy are presented in Chapter 4, with focus on optimising the preselection cuts to reduce the rate of background processes, including those previously unconsidered for this channel but found to be important as a consequence of this study. In addition, the reconstruction of the leptonically decaying W Boson from lepton and missing energy is described. The treatment of jets is introduced in Chapter 5, with the focus being again on the optimisation of preselection cuts. Studies presented here are on corrections for energy lost via both muons and neutrinos in semi-leptonic bdecays and preselection cuts based on the transverse momenta and b-weights of individual jets. The issues associated with combinatorial background and the use of jet charge to reduce it is also introduced here. The choice of jet algorithm is considered of great importance for this channel, thus is presented in detail in Chapter 6. Chapter 7 explores the reconstruction of the Higgs Boson from jet pairs, focusing on the segregation of jets by b-weight. The reconstruction of the t \overline{t} H^{0} system is studied with various techniques; an investigation of the use of jet charge to discriminate between b and \overline{b} jets is presented as a novel likelihood variable.Chapter 8 summarises the results obtained using the optimised preselection, jet algorithm and jet charge method. Systematic uncertainties are discussed throughout the thesis where relevant and also summarised.
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Tenaglia, Giovanni. "Performance studies of the CMS distributed analysis system in the associated Higgs boson production with top quarks." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7704/.
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L'obiettivo di questa tesi è studiare la fattibilità dello studio della produzione associata ttH del bosone di Higgs con due quark top nell'esperimento CMS, e valutare le funzionalità e le caratteristiche della prossima generazione di toolkit per l'analisi distribuita a CMS (CRAB versione 3) per effettuare tale analisi.
Nel settore della fisica del quark top, la produzione ttH è particolarmente interessante, soprattutto perchè rappresenta l'unica opportunità di studiare direttamente il vertice t-H senza dover fare assunzioni riguardanti possibili contributi dalla fisica oltre il Modello Standard. La preparazione per questa analisi è cruciale in questo momento, prima dell'inizio del Run-2 dell'LHC nel 2015. Per essere preparati a tale studio, le implicazioni tecniche di effettuare un'analisi completa in un ambito di calcolo distribuito come la Grid non dovrebbero essere sottovalutate. Per questo motivo, vengono presentati e discussi un'analisi dello stesso strumento CRAB3 (disponibile adesso in versione di pre-produzione) e un confronto diretto di prestazioni con CRAB2. Saranno raccolti e documentati inoltre suggerimenti e consigli per un team di analisi che sarà eventualmente coinvolto in questo studio.
Nel Capitolo 1 è introdotta la fisica delle alte energie a LHC nell'esperimento CMS. Il Capitolo 2 discute il modello di calcolo di CMS e il sistema di analisi distribuita della Grid. Nel Capitolo 3 viene brevemente presentata la fisica del quark top e del bosone di Higgs. Il Capitolo 4 è dedicato alla preparazione dell'analisi dal punto di vista degli strumenti della Grid (CRAB3 vs CRAB2). Nel capitolo 5 è presentato e discusso uno studio di fattibilità per un'analisi del canale ttH in termini di efficienza di selezione.
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Roberts, Rhys. "Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/evidence-for-the-associated-production-of-the-higgs-boson-and-a-top-quark-pair-with-the-atlas-detector(ae9de2a2-b533-41db-9eb7-b25ac77afcdf).html.
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This thesis presents analyses performed with proton-proton collision data collected with the ATLAS detector in 2015 and 2016 at √s=13 TeV. The measurement of so-called non-factorisation effects in the calibration of luminosity is presented. An estimate of the correction, and systematic uncertainty, due to non-factorisation on the calibration is calculated by measuring the proton bunch density profiles from the variation in the luminosity and distribution of reconstructed vertices during beam separation scans. The correction is applied to the calibrations of the total luminosity collected in both 2015 and 2016. A novel multivariate algorithm designed to reject non-prompt leptons (produced from the decays of b- and c-quarks) is presented, utilising information from nearby tracks to discriminate from prompt leptons (produced from W, Z and H boson decays). This algorithm is used to reject non-prompt backgrounds in the search for the associated production of a top quark pair and a Higgs boson (tt̄H) in multilepton final states with 36.1 fb⁻¹ of √s=13 TeV data. Multilepton states refer to the Higgs boson decaying into pairs of W bosons, Z bosons or τ leptons. The combination of the multilepton analysis with the other search analyses of tt̄H production in which the Higgs decays to pairs of photons, b-quarks and ZZ→4ℓ is also shown. The measured value of the signal strength of tt̄H production in data is μ(tt̄H) = 1.2 ± 0.3, corresponding to an observed (expected) discovery significance of 4.2σ (3.8σ) and constituting evidence for the tt̄H production mode.
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Wang, Chao. "Search for the production of the Higgs boson associated with a pair of top quarks with the Atlas detector at the LHC." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0433/document.
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La production du boson de Higgs associée à une paire de quarks top est l'un des modes de production de boson de Higgs les plus importants bien que toujours pas encore observé. Par conséquent, sa découverte est l'une des recherches les plus ambitieuse après la découverte Higgs: non seulement cela sera la première fois que nous pourrons observer ce mode de production du Higgs mais nous pourrons également en mesurer le couplage de Yukawa au quark top. Les résultats de ces mesures peuvent répondre aux questions fondamentales du Modèle Standard (MS) et peuvent également donner des indices de nouvelle physique au-delà du MS. Une analyse de la recherche de la production de boson de Higgs associée à une paire de quarks top dans des états finaux à trois leptons est présentée dans cette thèse. Cette analyse est réalisée avec des données collectées par le détecteur ATLAS en 2015 et 2016 pendant la campagne dite « Run 2 » et correspondant à une luminosité intégrée de 36.1 fb-1 à une énergie dans le centre de masse de 13 TeV. Elle utilise un algorithme d'arbre de décision renforcé pour discriminer le signal et le fond. Le bruit de fond dominant de faux leptons est estimé avec une méthode de matrice s’appuyant sur les données (Méthode de la Matrix). Pour un Higgs standard de 125 GeV, un excès d'événements par rapport au bruit de fond attendu d'autres processus MS est trouvé avec une signification observée de 2.2 écarts-types, comparé à une prédiction de 1.5 écart-type. Le meilleur ajustement pour la section efficace de production $t\bar tH$ est de $1.5^{+0.8}_{-0.7}$ fois l'espérance SM, consistant avec la valeur SM du couplage de Yukawa au quark topThe production of the Higgs boson associated with a pair of top quarks is one of the most important Higgs boson production modes yet still not observed. Therefore, its discovery is one of the most challenging searches after the Higgs discovery: not only will it be the first time we can observe this Higgs production mode but also we will be able to measure its Yukawa coupling to the top quark. The measured results can answer the basic question of the Standard Model (SM) and can also search for any hints of new physics beyond the SM prediction. An analysis searching for the production of the Higgs boson associated with a pair of top quarks in three leptons final states is presented in this thesis. It is performed with the data collected by the ATLAS detector in 2015 and 2016 during the so-called « Run 2 » campaign corresponding to an integrated luminosity of 36.1 fb−1 at a center of mass energy of 13 TeV. It uses a boosted decision tree algorithm to discriminate between signal and background. The dominant background of fake leptons is estimated with the data-driven matrix method (Matrix Method). For a 125 GeV Standard Model Higgs boson, an excess of events over the expected background from other SM processes is found with an observed significance of 2.2 standard deviations, compared to an expectation of 1.5 standard deviations. The best fit for the $t\bar tH$ production cross section is $1.5^{+0.8}_{-0.7}$ times the SM expectation, consistent with the SM value of the Yukawa coupling to top quarks
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Parks, Brandon Scott. "Search for the Higgs Boson in the ZH → vvbb̄ Channel at CDF Run II." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1215108702.
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Häfliger, Petra. "Associated MSSM Higgs production with heavy quarks : SUSY-QCD corrections & impact of Ao on the mSUGRA parameter space /." Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16970.
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Warsinsky, Markus. "Studies of b-associated production and muonic decays of neutral Higgs bosons at the ATLAS experiment within the Minimal Supersymmetric Standard Model." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1221746748987-12927.
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This thesis presents a Monte Carlo study of neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) decaying into muons at the Atlas experiment at the CERN Large Hadron Collider. Signal and background processes are simulated using novel Monte Carlo generators that incorporate parts of higher order corrections and are expected to give a more accurate prediction than previous programs. The SHERPA Monte Carlo generator is validated for its use in the analysis and compared to results obtained with other programs. Where possible, the Monte Carlo event samples are normalized to higher order calculations. To increase the available Monte Carlo statistics, this study is based on the ATLAS fast detector simulation ATLFAST. Differences between ATLFAST and the detailed detector simulation of ATLAS are examined, and, where possible, correction procedures are devised. A cut based analysis is performed assuming an integrated luminosity of 30 inverse femtobarns, and optimized with respect to the discovery potential for MSSM Higgs bosons. The systematic uncertainties of the event selection and the Monte Carlo predictions are estimated. A method that can be used to estimate the background from data is presented and evaluated. Last, the discovery potential of the \Atlas experiment in the CP conserving benchmark scenarios of the MSSM is evaluated. One or more of the neutral Higgs bosons of the MSSM can be discovered in the muonic decay mode using 30 inverse femtobarns of data for low masses of the pseudoscalar boson A, if the model parameter tan(beta) is at least 20. For higher masses of the A, tan(beta) would need to be significantly higher to ensure a discovery in the studied decay channel. The sensitivity of ATLAS to MSSM Higgs bosons is multiple times larger than the one of previous and currently running experimentsDie vorliegende Arbeit präsentiert eine Monte Carlo Studie zu neutralen Higgs-Bosonen des Minimal Supersymmetrischen Standardmodells (MSSM) im myonischen Zerfallskanal am Atlas Experiment am Large Hadron Collider des CERN. Signal- und Untergrundprozesse werden mit neuartigen Monte Carlo Ereignisgeneratoren simuliert, die Teile der Korrekturen höherer Ordnung beinhalten, und von denen eine verbesserte Vorhersage erwartet wird im Vergleich zu herkömmlichen Programmen. Der SHERPA Monte Carlo Ereignisgenerator wird auf seine Brauchbarkeit für die Analyse überprüft und mit Ergebnissen anderer Programme verglichen. Sofern möglich werden die erstellten Monte Carlo Datensätze mittels Rechnungen zu höheren Ordnungen normiert. Um eine hinreichend große Statistik von simulierten Daten zu erhalten, wird die schnelle Detektorsimulation des ATLAS Detektors ATLFAST verwendet. Unterschiede zwischen der vollständigen Detektorsimulation und ATLFAST werden untersucht, und sofern möglich, Korrekturverfahren entwickelt. Eine schnittbasierte Analyse wird durchgeführt unter der Annahme einer integrierten Luminosität von 30 inversen femtobarn und optimiert mit Hinblick auf das Entdeckungspotenzial für MSSM Higgs-Bosonen. Die systematischen Unsicherheiten der Ereignisauswahl und der Monte Carlo-Vorhersagen werden abgeschätzt. Eine Methode zur Messung des Untergrundes in Daten wird vorgestellt und überprüft. Schliesslich wird das Entdeckungspotenzial des ATLAS Experiments in Vergleichspunkten für CP erhaltende Szenarien des MSSM ermittelt. F\ür niedrige Massen des pseudoskalaren Higgs-Bosons A kann mindestens eines der neutralen Higgs-Bosonen des MSSM im myonischen Zerfallskanal entdeckt werden, sofern der Modellparameter tan(beta) mindestens 20 ist. Für hohe Massen des A muss ein wesentlich größeres tan(beta) in der Natur realisiert sein, um eine Entdeckung im untersuchten Zerfallskanal zu ermöglichen. Die Sensitivität von ATLAS auf Higgs-Bosonen des MSSM ist um ein Vielfaches höher als diejenige bisheriger oder momentan laufender Experimente
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Hohn, David [Verfasser]. "Search for top-quark-pair associated Higgs production with tau leptons using the ATLAS detector at the LHC / David Hohn." Bonn : Universitäts- und Landesbibliothek Bonn, 2019. http://d-nb.info/1185576126/34.
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Shaw, Christian Alexander. "Standard model Higgs boson analysis via associated top production and hadronic decay using the ATLAS detector at the CERN LHC." Thesis, University of Glasgow, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443421.
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Tonon, Nicolas. "Search for the associated production of a single top quark and a Z or Higgs boson with the CMS experiment." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE022.
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Cette thèse présente 4 études basées sur les données collectées par CMS durant le Run 2 du LHC. Une première recherche de la production d’un quark top solitaire et d’un boson Z (tZq) est réalisée. Ce processus rare permet de sonder des couplages du Modèle Standard, et pourrait être sensible à des processus de nouvelle physique. Cette étude cible l'état final trileptonique et a permis la mise en évidence du processus tZq. Une deuxième recherche de la production d’un quark top solitaire et d’un boson de Higgs (tH) dans des états finaux multileptoniques est réalisée. Il s’agit du seul processus sensible au LO au signe du couplage de Yukawa du quark top. Des contraintes sont placées sur le Yukawa du top, et sur la section efficace de tH. L’analyse est ré-adaptée afin de rechercher des processus FCNC ayant des états finaux similaires. Enfin, une étude du vieillissement dû à l’irradiation du trajectographe à pistes est présentéeThis thesis presents 4 different studies based on the data collected by CMS during the Run 2 of the LHC. Firstly, a search for the production of a single top quark and a Z boson (tZq) is conducted. This rare process probes Standard Model couplings, and may be sensitive to new physics processes. This search targets the trilepton final state and resulted in an evidence for the tZq process. A second analysis targets the production of a single top quark and a Higgs boson (tH) in multileptonfinal states. It is the only process sensitive at LO to the sign of the top quark Yukawa coupling. Constraints are placed on the value of the top quark Yukawa, and on the tH cross section. In addition, the analysis is re-adapted to search for FCNC processes with similar final states. Finally, a study of the ageing due to irradiation of the strip tracker is presented
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Li, Changqiao. "b-tagging calibration and observation of Higgs boson decays to a pair of bottom quarks with the atlas detector." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS620.
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Cette thèse décrit dans un premier temps la mesure d’efficacité d’identification des jets b grâce à la méthode tag-and-probe utilisant les données enregistrées par le détecteur ATLAS en 2015 et 2016. La méthode de mesure de l’efficacité, la sélection des objets, des événements et des jets sondes, l’évaluation des incertitudes systématiques et statistiques sont présentées. Les efficacités d’identification des jets b ont été mesurées en fonction du moment transverse des jets, de leurs pseudo-rapidités et du nombre moyen de collisions (pile-up). Les efficacités mesurées dans les données ont été comparées aux prédictions des simulations, et ainsi des facteurs d’échelles ont été extraits. Les valeurs obtenues sont proche de un, avec des incertitudes allant de 2% à 12%.Dans un deuxième temps, cette thèse décrit la recherche de la désintégration du boson de Higgs décrit par le modèle standard en une paire quark/anti-quark b dans le canal de production associée avec un boson vecteur. Deux résultats obtenus sont décrits: le premier avec les données collectées par ATLAS avec de collisions protons protons à 13 TeV lors du Run2 du LHC jusqu’en 2016 (36.1 fb-1), puis un second ajoutant les données obtenues dans les mêmes conditions en 2017 (44 fb-1).Le premier résultat est présenté avec une description de la technique de reconstruction des objets, de la sélection des événements et de leur classification, des techniques de discrimination entre le signal et le bruit de fond, de la modélisation des principaux bruits de fond, des propriétés du signal ainsi que de l’interprétation des résultats. Pour le deuxième étude, basée sur les 80 fb-1 données collectées, seules les différences d’avec la première étude sont mises en lumière.Les deux résultats apportent une forte évidence statistique de la production avec des significances respectives de 3.5 et 4.9 déviation standard. L’intensité du signal, définie comme le rapport entre la mesure et la prédiction théorique de la section efficace multipliée par le rapport d’embranchement , obtenue avec les données est , ce qui indique un bon accord entre les données et le modèle standard. La combinaison du résultat basé sur les données à 80 fb-1 obtenues à une énergie dans le centre de masse de 13 TeV avec les données obtenues avec une énergie inférieure (7 et 8 TeV) en 2011 et 2012, ainsi qu’avec les recherches de la désintégration dans les autres canaux de production (fusion de bosons vecteurs, production associée avec une paire de quark top) a permis l’observation de la désintégration avec une significance statistique de 5.4 déviation standard, et une mesure de l’intensité de signal . Une combinaison du résultat basée sur les données à 80 fb-1 obtenues à une énergie dans le centre de masse de 13 TeV avec les recherches dans le même canal de production et avec les mêmes données brutes dans les états finaux en deux photons et ZZ∗ → 4l, a permis l’observation de la production associée du boson de Higgs avec un boson vecteur avec une significance statistique de 5.3 deviation standard, et une mesure de l’intensité de signal , ce qui confirme le bon accord avec la théorie du modèle standardThis thesis firstly describes a measurement of the b-jet tagging efficiency with a tag-and-probe method using data recorded by the ATLAS detector in 2015 and 2016. The efficiency measurement method, the object selection, the event and probe jet selection, the evaluation of the statistical and systematic uncertainties, and the final results are discussed. The b-tagging efficiencies have been measured as a function of the jet transverse momentum, pseudorapidity and of the average number of pile-up collisions. The efficiencies measured in data have been compared to those predicted from simulation, and simulation-to-data efficiency scale factors have been determined. The efficiency scale factors are close to unity, with total uncertainty ranging between 2% and 12%. The second part of this thesis focuses on the search for the decays of the Standard Model (SM) Higgs boson to bottom quarks in the associated production mode with vector bosons. Two measurements have been performed and are described here: the first one is based on of 13 TeV pp collisions recorded by ATLAS during the LHC Run-2 until 2016; the second one includes the additional of 13 TeV pp collisions recorded in 2017. For the study based on of data, the object reconstruction, event selection and classification, the techniques to discriminate the signal from the background, the main background and their modelling, the signal properties and the interpretation of results are discussed. For the study based on data, the main difference from the previous study are highlighted. Both results provide a strong evidence of the process, with statistical significances of 3.5 and 4.9 standard deviations, respectively. The signal strength, defined as the ratio between the measured cross section times branching ratio and the SM prediction, is measured with the 2015–2017 dataset to be , indicating good agreement with the SM. The combination of the results based on of 13 TeV collisions with the results of the same analysis performed on data collected at lower (7 and 8 TeV) centre-of-mass energies in 2011 and 2012, and witht those of the searches of decays in other Higgs boson production modes (vector-boson fusion, associated production with a top-quark pair) have led to the observation of the decay with a significance of 5.4 standard deviations, and to a measurement of the signal strength . A combination of the results of the results based on of 13 TeV collisions with the results of searches for the same production mode on the same amount of data in the diphoton and ZZ∗ → 4l Higgs boson final states has led to the observation of VH production with a significance of 5.3 standard deviations, and to a measurement of the signal strength , in good agreement with the SM
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Asbah, Nedaa Alexandra. "Search for the Production of a Standard Model Higgs Boson in Association with Top-Quarks and Decaying into a Pair of Bottom-Quarks with 13 TeV ATLAS Data." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19311.
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Die vorliegende Arbeit beschreibt die Suche nach der Produktion des Standardmodell Higgs-Bosons in Assoziation mit einem Top-Antitop-Quarkpaar ttH). Der verwendete Datensatz basiert auf einer integrierten Luminositat von 36.1 1/fb, aufgenommen mit dem ATLAS Detektor am Large Hadron Collider in den Jahren 2015 und 2016. Die selektierten Ereignisse enthalten entweder ein oder zwei Leptonen vom Zerfall des Top-Antitop-Quarkpaares. Die Sensitivität der Analyse wurde erhöht, indem die Ereignisse in unterschiedliche Regionen unterteilt wurden, basierend auf der Anzahl der Jets sowie der Wahrscheinlichkeit b-Jets zu enthalten. Methoden basierend auf multivariaten Analysetechniken wurden entwickelt, um ttH Signalereignisse vom Untergrund zu separieren, der von der Produktion von Top-Antitop-Quarkpaaren mit zusätzlichen b-Jets dominiert wird. Alle in der Analyse verwendeten Regionen wurden in einem Profile-Likelihood-Fit kombiniert, um die Vorhersagen des Untergrunds einzuschr{\"a}nken und die systematischen Unsicherheiten zu reduzieren. Ein Überschuss an Ereignissen über dem erwarteten Standardmodell-Untergrund wurde mit einer beobachteten (erwarteten) Signifikanz von 1.4 (1.6) Standardabweichungen gemessen. Die Daten schliessen ttH Signalstärken von mehr als 2.0 mit einem Konfidenzniveau von 95% aus.This thesis presents the search for the Standard Model Higgs boson produced in association with a pair of top-quarks (ttH). The analysis uses a 36.1 1/fb dataset of proton-proton collisions collected with the ATLAS detector, at the Large Hadron Collider during 2015 and 2016. The selected events contain either one or two leptons from the decay of the top-quark pair. In order to improve the sensitivity of the search, events are split in regions according to the number of jets and how likely these events are to contain b-jets. Methods based on multivariate techniques were developed and applied in the signal-enriched regions to discriminate ttH events against background events being dominated by top pair production with additional b-jets. All analysis regions are combined in a statistical model using a profile likelihood fit to constrain the background predictions and reduce the systematic uncertainties. An excess of events over the expected Standard Model background is found with an observed (expected) significance of 1.4 (1.6) standard deviations. A ttH signal strength larger than 2.0 is excluded at the 95% confidence level.
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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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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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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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BESCHI, ANDREA. "Measurement of the associated production of top quark pairs with a Higgs boson in the diphoton final state with the CMS detector." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/261931.
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La tesi presenta l'analisi dei dati collezionati nel 2016 e nel 2017 dall'esperimento CMS presso il Large Hadron Collider per effettuare una misura della sezione d'urto della produzione associata di bosoni di Higgs e coppie di quark top-antitop (ttH). Si è scelto il canale di decadimento del bosone di Higgs in due fotoni in quanto è uno tra i canali più sensibili dal punto di vista sperimentale. L'analisi è basata su 35.9 fb−1 e 41.5 fb−1di dati raccolti rispettivamente nel 2016 e nel 2017 in collisioni protone-protone ad un'energia del centro di massa di 13 TeV.
All'inizio di questo lavoro la misura della sezione d'urto per il processo ttH mostrava una leggera deviazione, di circa due deviazioni standard, dalla predizione del modello standard (MS). Una misura più precisa del processo è stata dunque necessaria per verificare se la deviazione osservata fosse dovuta a una fluttuazione statistica o a fenomeni non predetti dal MS.
La scelta del canale di decadimento in due fotoni è dettata dallo stato finale completamente ricostruito e dal buon rapporto di eventi di segnale e di fondo, ovvero eventi dovuti a processi differenti ma con stato finale simile. La segnatura sperimentale di un bosone di Higgs che decade in due fotoni è la presenza di un picco risonante nello spettro di massa invariante delle coppie di fotoni. La produzione ttH può essere identificata in modo esclusivo grazie alla presenza nello stato finale di prodotti di decadimento dei quark top.
La sezione d'urto del processo ttH è estratta da un fit allo spettro di massa invariante delle coppie di fotoni. La funzione utilizzata per il fit è basata su un modello di segnale, costruito in accordo con quanto predetto da simulazioni dei processi di produzione di bosone di Higgs, e un modello di background, derivato direttamente dal fit dei dati. Il fit è effettuato lasciando come parametro libero la forza del segnale μ, definita come il rapporto tra la sezione d'urto misurata e quella predetta dal MS. L'analisi dei dati del 2016 è risultata in una misura pari a μ = 2.2+0.9−0.8, escludendo l'ipotesi di solo fondo al livello di 3.2 deviazioni standard, mentre il valore atteso dal MS per un bosone di Higgs è di 1.5. Il raffinamento delle tecniche di analisi dati ha permesso di migliorare la sensitività sperimentale di più del 50%, misurando con i dati del 2017 un valore di μ = 1.3+0.7−0.5. L'ipotesi di solo fondo è rigettata a livello di 3.1 deviazioni standard, metre l'attesa del MS è di 2.2. La combinazione dei due risultati permette di misurare μ = 1.7+0.6-0.5 e corrisponde ad una significatività statistica di 4.1 deviazioni standard.
L'analisi dei dati del 2016, in combinazione con le analisi dei dati che riguardano stati finali in cui il bosone di Higgs decade in quark b, bosoni vettori o leptoni τ, ha permesso la prima osservazione sperimentale del processo ttH. Il risultato è basato sui dati raccolti nel 2016 ad energia del centro di massa di 13 TeV, oltre che ai dati raccolti nel 2011 e 2012 a energia del centro di massa di 7 e 8 TeV, rispettivamente. Il risultato della combinazione dei differenti canali è μ = 1.26+0.31−0.26, in accordo con il MS. L'ipotesi di solo fondo è rigettata a livello di 5.1 deviazioni standard. Questa misura dimostra l'esistenza dell'accoppiamento diretto del bosone di Higgs a quark top, e quindi a quark di tipo up.This thesis presents the analysis of the data collected in 2016 and in 2017 by the CMS detector at the Large Hadron Collider to perform a precise measurement of the cross section of the Higgs boson production in association with a pair of top-antitop quarks (ttH). The diphoton decay channel of the Higgs boson is exploited to perform the measurement, as among the most sensitive channels. The analysis exploits 35.9 fb−1 of data collected in 2016 and 41.5 fb−1 collected in 2017 in proton-proton collisions at a centre-of-mass energy of 13 TeV. At the beginning of this work, the measured cross section of the ttH process showed a mild departure from the standard model (SM) expectation of about two standard deviations. A more precise determination was necessary to ascertain whether the observed tension was due to a statistical fluctuation or to some unpredicted feature. The choice of the diphoton decay channel is due to the fully reconstructed final state and to the low number of events arising from different processes but with similar topology, namely background. The experimental signature of a Higgs boson decaying to a pair of photons is the presence of a narrow resonant peak arising in the invariant mass distribution of the photon pairs. The ttH production can be exclusively identified by the presence in the final state of the decay products of the top quarks. The ttH production rate is extracted from a fit to the invariant mass spectrum of the photon pairs. The fit function is based on a signal model, built from simulation of the Higgs boson production processes, and a background one, derived directly from fitting the data.The fit is performed with floating the signal strength μ, defined as the ratio between the measured ttH production cross section and the SM expectation. The analysis of the 2016 data resulted in an observed value of μ = 2.2+0.9−0.8, rejecting the background-only hypothesis at 3.2 standard deviations, where 1.5 is expected for a SM Higgs boson. The refinement of the techniques exploited for the data analysis lead to an improvement in the sensitivity of more than 50 % in the analysis of the 2017 data, with μ = 1.3+0.7−0.5, rejecting the background-only hypothesis at 3.1 standard deviations, where 2.2 are expected for a SM Higgs boson. The combination of the two analyses resulted in an observed signal strength of μ = 1.7+0.6-0.5, corresponding to a significance of 4.1 standard deviations. The analysis of the 2016 data, together with the analyses targeting final states with the Higgs boson decaying in b quarks, vector bosons and τ leptons, allowed the first experimental observation of the ttH process. The result exploited the analysis of the data collected in 2016 at a centre-of-mass energy of 13 TeV, as well as the data collected in 2011 and 2012 at a centre-of-mass energy of 7 and 8 TeV, respectively. The best fit value of the combination of the different channels is μ = 1.26+0.31−0.26, in agreement with the SM expectation. The background-only hypothesis is rejected at the level of 5.1 standard deviations. This result proves for the first the tree-level coupling of the Higgs boson with the top quarks and, hence, with an up-type quark.
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Bryant, Patrick. "Search for Pair Production of Higgs Bosons in the Four Bottom Quark Final State Using Proton-Proton Collisions at √S = 13 Tev with the ATLAS Detector." Thesis, The University of Chicago, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10974446.
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A search for Higgs boson pair production in the four b-jet final state is carried out with up to 36.1/fb of LHC proton--proton collision data collected at √s = 13 TeV with the ATLAS detector in 2015 and 2016. Three benchmark signals are studied: a spin-2 graviton decaying into a Higgs boson pair, a scalar resonance decaying into a Higgs boson pair, and Standard Model non-resonant Higgs boson pair production. This thesis presents a search in events with four individually resolved b-tagged jets. Higgs bosons produced with large momenta are reconstructed as single large radius jets with substructure. The analysis of this topology is presented in CERN-THESIS-2018-118. The two analyses are statistically combined and upper limits on the production cross section of Higgs boson pairs times branching ratio to four b-quarks are set in each model. The combined result searches for resonance masses in the range 260–3000 GeV. No significant excess is observed; the largest deviation of data over prediction is found at a mass of 280 GeV, corresponding to 2.3 standard deviations globally. The observed 95% confidence level upper limit on the non-resonant production is 13 times the Standard Model prediction.
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Ma, Yanhui. "Observation du mode de désintégration H→bb et de la production associée de VH avec le détecteur ATLAS." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS099/document.
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Une recherche du boson de Higgs du Modèle Standard produit en association avec un boson W ou Z et se désintégrant en une paire quark-antiquark b a été effectuée avec le détecteur ATLAS. Les données de collisions proton-proton utilisées ont été accumulées durant le Run 2 du Grand Collisionneur de Hadrons du CERN à une énergie dans le centre de masse de 13 TeV, et correspondent à une luminosité intégrée de 79.8 fb⁻¹. Trois canaux contenant zéro, un ou deux leptons chargés (électrons ou muons) sont considérés, correspondant à chacune des désintégrations leptoniques d'un boson W ou Z: Z->vv, W->lv et Z->ll. Pour un boson de Higgs de masse 125 GeV, un excès d'événements par rapport aux bruits de fonds des autres processus du Modèle Standard est observé avec un niveau de signification statistique de 4.9 déviations standard, à comparer à 4.3 attendues. Le rapport du nombre d'événements observé au nombre attendu est mesuré être 1.16 +0.27/-0.25 = 1.16 +/-0.16(stat) +0.21/-0.19(syst). Ce résultat est combiné avec d'autres d'ATLAS sur la recherche du boson de Higgs se désintégrant dans le mode bbbar, utilisant des données du Run 1 et du Run 2. Le niveau de signification mesuré (attendu) pour ce mode de désintégraion est de 5.4 (5.5) déviations standard, ce qui en constitue la première observation directe. De plus, une combinaison des résultats du Run 2 sur la recherche de la production associée du boson de Higgs et d'un boson W ou Z conduit à un niveau de signification observé (attendu) de 5.3 (4.8) déviations standard, et donc à la première observation de ce mode de productionA search for the Standard Model Higgs boson produced in association with a W or Z boson, and decaying to a bb pair has been performed with ATLAS detector. The data were collected in proton-proton collisions during Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13 TeV, and correspond to an integrated luminosity of 79.8 fb⁻¹. Three channels containing zero, one and two charged leptons (electrons or muons) have been considered to target each of the leptonic decays of the W or Z boson, Z->vv, W->lv et Z->ll, referred to as as the 0-lepton, 1-lepton and 2-lepton channels, respectively. For a Higgs boson mass of 125 GeV, an excess of events over the expected background from other Standard Model processes is found with an observed significance of 4.9 standard deviations, compared to an expectation of 4.3 standard deviations. The ratio of the measured signal events to the Standard Model expectation equal 1.16 +0.27/-0.25 = 1.16 +/-0.16(stat) +0.21/-0.19(syst). The result is also combined with the other results from the searches for the Higgs boson in the bb 18 decay mode in Run 1 and Run 2, the combination yields an observed (expected) significance of 5.4 (5.5) 20 standard deviations, and therefore provides a direct observation of the Higgs boson decay into a bb pair. In addition, a combination of Run 2 results searching for the Higgs boson produced in association with a W or Z boson yields an observed (expected) significance of 5.3 (4.8) standard deviations, and therefore provides a direct observation of Higgs boson being produced in association with a W or Z boson
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Gargiulo, Simona [Verfasser], and Christian [Akademischer Betreuer] Weiser. "Measurement of the Higgs boson decay to a pair of b-quarks in the associated production with a vector boson with the ATLAS detector." Freiburg : Universität, 2021. http://d-nb.info/1236550706/34.
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Biondi, Silvia <1990>. "Study of the Associated Production of the Higgs Boson with a Top Quark Pair in a Boosted Regime in the ATLAS Experiment at LHC." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/7811/1/Biondi_Silvia_tesi.pdf.
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The measurements of the pp → ttH + X signal strength (μ = σ obs/σ ttH SM ) and its upper limit at a center-of-mass energy of pp collision of 13 TeV are presented in this thesis. The pp data collected with the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.5 fb^(−1), have been submitted to a detailed analysis. The ttH signal strength and its upper limit have been measured searching for the decays H → bb and tt→ lνbqq ̄ b. Two different analysis approaches are used. In the first (namely “resolved”), the procedure uses standard identification and reconstruction algorithms. In the second (namely “combined”), the events are separated in two exclusive regimes, including events containing the hadronically decaying top quark with a low transverse momentum (pT < 250 GeV) and the boosted ones with the opposite requirement, where the partially overlapped jets coming from high pT tops are suitably identified, reconstructed and tagged. The boosted sample is sensitive to a significantly different kinematic region and provides additional information. The measured signal strength is 1.4±0.5 and 1.2±0.5 respectively for the resolved and the combined analysis. A signal strength larger than 2.3 and 2.0 can be excluded at the 95% confidence level respectively for the resolved and the combined analysis. Both results are compatible with the prediction of the Standard Model (μ = 1).In questa tesi è presentata la misura della “signal strength” (μ = σ obs/σ ttH SM ) e del limite superiore della produzione associata di un bosone Higgs con una coppia di quark top, pp → ttH + X ad un’energia del centro di massa di 13 TeV. I dati sono stati acquisiti dall’esperimento ATLAS nel 2015 e 2016, corrispondenti ad una luminosità integrata di 36.5 fb^(-1). La signal strength del canale ttH e il suo limite sono stati misurati studiando i canali di decadimento H → bb e tt→ lνbqq ̄ b, con due differenti approcci. Nel primo (detto “resolved”), sono stati usati gli algoritmi standard di identificazione e ricostruzione come nelle precedenti analisi già pubblicate. Nel secondo (detto “combined”), gli eventi sono separati in due regimi esclusivi, includendo quelli contenenti il quark top adronico con un basso momento trasverso (pT < 250 GeV) e quelli boosted con la richiesta opposta, dove i jet parzialmente sovrapposti provenienti da top con alto pT vengono ricostruiti e identificati con metodi innovativi. Il campione di eventi boosted è sensibile ad una regione cinematica significativamente differente e, per questo, fornisce informazioni aggiuntive. La signal strength misurata è 1.4±0.5 e 1.2±0.5 rispettivamente per l’analisi resolved e combined. Una signal strength più grande di 2.3 e 2.0 può essere esclusa con un livello di confidenza del 95%, rispettivamente per l’analisi resolved e combined. Entrambi i risultati sono compatibili con la previsione del Modello Standard (μ = 1).
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Rieger, Marcel [Verfasser], Hans Martin [Akademischer Betreuer] Erdmann, and Alexander [Akademischer Betreuer] Schmidt. "Search for Higgs boson production in association with top quarks and decaying into bottom quarks using deep learning techniques with the CMS experiment / Marcel Rieger ; Hans Martin Erdmann, Alexander Schmidt." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/119571503X/34.
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Brown, Jonathan. "Search for WH associated production in the lνbb final state using the DØ detector at the Tevatron." Phd thesis, Université Paris-Diderot - Paris VII, 2011. http://tel.archives-ouvertes.fr/tel-00918068.
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Le Modèle Standard est le cadre qui permet de décrire les interactions entre les particules et leur dynamique. Le mécanisme de Higgs est une solution pour introduire naturellement un terme de masse dans la description théorique de ce modèle. Après la rupture spontanée de la symétrie électrofaible, une nouvelle particule scalaire massive est introduite, le boson de Higgs. Comme celui-ci n'a pas encore été découvert, la recherche du boson de Higgs est effectué au Tevatron, qui est un collisionneur pp ̄ à une énergie au centre de masse de 1.96 TeV. Pour MH = 135 GeV, le mode de désintégration dominant est H → bb ̄. L'analyse présentée dans ce document est axée sur le domaine en masse 100 < MH < 150 GeV, dans le canal où le boson de Higgs est produit en association avec un boson W se désintègrant en un lepton chargé (électron ou muon) et un neutrino. L'étude de cet état final repose sur les informations recueillies auprès de toutes les parties du détecteur DØ. Un résultat basé sur 5.3 fb−1 de collisions récoltées durant le RunII du Tevatron est présenté ici. Afin d'augmenter la sensibilité au signal, l'analyse est séparée en sous-canaux en fonction de la saveur du lepton considéré, le nombre de jets dans l'état final, le nombre de jets identifiés comme provenant de quarks b et par périodes de prise de données. Après sélection des événements, une technique d'analyse multivariée est utilisée pour séparer les événements de type signal du bruit de fond physique et instrumental attendu. Comme un bon accord entre les données et simulation est observé, une limite supérieure observée (attendue) de 4.5 (4.8) est placée (pour MH = 115 GeV) sur le rapport entre la section efficace pp ̄ → W H multipliée par le rapport d'embranchement H → bb ̄ et la prédiction du Modèle Standard, à 95% de niveau de confiance. Alors que les dernières données du Tevatron sont en cours d'analyse, les perspectives de recherche au Tevatron sont exposées ici. Les améliorations futures pour la publication finale sur la recherche dans le canal WH → lνbb ̄ sont présentées. La masse invariante dijet étant la variable la plus discriminante, l'amélioration de la résolution du pic de masse est un enjeu important, ainsi que l'optimisation de l'utilisation des outils d'identification de jets de quarks b et du discriminant final. Une amélioration significative est obtenue au niveau de la limite.
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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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Fink, Simon [Verfasser], and Th [Akademischer Betreuer] Müller. "Probing the Top-Yukawa Coupling by Searching for Associated Higgs Boson Production with a Single Top Quark at the CMS Experiment / Simon Fink. Betreuer: Th. Müller." Karlsruhe : KIT-Bibliothek, 2016. http://d-nb.info/1110969635/34.
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Davis, Kevin Patrick. "Measurement of the bottom quark production cross section in proton-antiproton collisions at a center-of-mass energy 630 GeV using muons with associated jets." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/284341.
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We have measured the b-quark production cross section fory
< 1 using a sample of muons with associated jets collected with the D⊘ detector in pp̄ collisions at √s = 630 GeV at the Fermilab Tevatron. The measured b-quark cross section is consistent in shape with O(α³s) QCD predictions, but exceeds them in normalization by roughly a factor of 2.5.
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Nechansky, Filip [Verfasser]. "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 / Filip Nechansky." Berlin : Humboldt-Universität zu Berlin, 2021. http://d-nb.info/1236896971/34.
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Hageböck, Stephan [Verfasser]. "Search for the H -> bb Decay of the Standard Model Higgs Boson in Associated Production with Vector Bosons Using ATLAS Data at s = 8 TeV / Stephan Hageböck." Bonn : Universitäts- und Landesbibliothek Bonn, 2018. http://d-nb.info/1173789545/34.
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Bokan, Petar [Verfasser]. "Pair production of Higgs bosons in the final state with bottom quarks and τ leptons in the ATLAS experiment: Search results using LHC Run 2 data and prospect studies at the HL-LHC / Petar Bokan." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2021. http://d-nb.info/1230824421/34.
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Asbah, Nedaa Alexandra [Verfasser], Judith [Gutachter] Katzy, Thomas [Gutachter] Lohse, and Hannes [Gutachter] Jung. "Search for the Production of a Standard Model Higgs Boson in Association with Top-Quarks and Decaying into a Pair of Bottom-Quarks with 13 TeV ATLAS Data / Nedaa Alexandra Asbah ; Gutachter: Judith Katzy, Thomas Lohse, Hannes Jung." Berlin : Humboldt-Universität zu Berlin, 2018. http://d-nb.info/1185666214/34.
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Therhaag, Jan [Verfasser]. "Search for the H→bb decay mode of the Standard Model Higgs boson in associated production with a vector boson in proton-proton collisions at √s=8TeV with the ATLAS experiment / Jan Therhaag." Bonn : Universitäts- und Landesbibliothek Bonn, 2014. http://d-nb.info/1054691649/34.
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Maier, Benedikt [Verfasser], and Th [Akademischer Betreuer] Müller. "Search for the associated production of a single top quark and a Higgs boson in the H to bbbar decay channel at 8 and 13 TeV with the CMS experiment / Benedikt Maier. Betreuer: Th. Müller." Karlsruhe : KIT-Bibliothek, 2016. http://d-nb.info/109943243X/34.
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Pogorelov, Yury. "A search for the associated Higgs production in the Tau channel." 2007. http://etd.nd.edu/ETD-db/theses/available/etd-07192007-233028/.
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Thesis (Ph. D.)--University of Notre Dame, 2007.Thesis directed by Anna Goussiou and Randal Ruchti for the Department of Physics. "July 2007." Includes bibliographical references (leaves 126-128).
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Hofmann, Franziska [Verfasser]. "Influence of the supersymmetric bottom sector on higgs production and decay / vorgelegt von Franziska Hofmann." 2009. http://d-nb.info/996637427/34.
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Kok-Wee, Song. "Associated Production of The Light Pseudoscalar Higgs Boson with Chargino pair in NMSSM." 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0016-0109200613413706.
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Song, Kok-Wee, and 宋國維. "Associated Production of The Light Pseudoscalar Higgs Boson with Chargino pair in NMSSM." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/73290707511687468766.
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碩士國立清華大學
物理學系
94
Supersymmetry is the symmetry between fermion and boson and this symmetry is very useful. Supersymmetry have many applications in physics, sometime it can solve some of the difficult problem. Minimal Supersymmetric Standard Model (MSSM) is the model which is minimally embedding super- symmetry into Standard Model. MSSM has several advantages, especially it give a solution to the hierarchy problem. Although this model is very attractive, MSSM has its own difficulty, it is “μ-problem”. This difficulty can be removed by introducing a new singlet scalar Higgs field and extended MSSM to the model call Next-to-Minimal Supersymmetry Standard Model. The NMSSM has an additional new pseudoscalar singlet Higgs and a new singlino in contrast to the MSSM. This model has some modification of the property of pseudoscalar Higgs boson. First, NMSSM give another new pseudoscalar Higgs into the theory which could be very light even less than a GeV, but in MSSM the pseudoscalar Higgs is very haevy (always a few hundred GeV). Secondly, even the gauge singlet property of this pseudoscalar Higgs, but it still posses a non-zero coupling to the charginos, neutralinos as well as the Higgs bosons. These two unusual property provided us a way to test NMSSM and distinguish it from MSSM. The main object of this paper is to study the cross section of the e+e− annihilation to produce the Chargino pair associated with the ligth pseudoscalar Higgs radiation (e+e−→χ+χ−A1). From the calculation result, we also con- clude that the cross section of this process is not small in the cases with A1 has a large singlet mixture and χ+χ−A1 has not small coupling. It may be able to detect in the future ILC. We also included the calculation of the proton collider which is for the test at LHC.
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Wang, Bo-Ting, and 王柏庭. "Comparison of Two Schemes For Higgs Production Associated with Heavy Quark Pairs using MadGraph." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/54750008927207962091.
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碩士國立臺灣大學
物理研究所
101
Some Beyond the Standard Model (BSM) Higgs particle may interact strongly with other particles at energy scales presently studied at the LHC, the study of Higgs production associated with heavy quark pairs may help us search for these BSMs. We compare two different schemes, the 4 flavour scheme and the 5 flavour scheme, to describe this process at LO + n jet by merging matrix element and parton shower approach on MadGraph 5 interface to PYTHIA. We show that the 4 flavour scheme may provide better description than the 5 flavour scheme at LO + n jet level.
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Sousa, Mário José da Cunha Sargedas de 1984. "Search for the higgs boson at ATLAS/LHC, in associated production with a Z boson." Doctoral thesis, 2017. http://hdl.handle.net/10451/34141.
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Tese de doutoramento, Física, Universidade de Lisboa, Faculdade de Ciências, 2017A mechanism of spontaneous symmetry breaking was used to explain the mass of elementary particles and predicted the existence of the Higgs boson. The Higgs boson was discovered in 2012 by the ATLAS and CMS experiments at the LHC with a mass of about 125 GeV. It now becomes necessary to study this new boson in order to validate the Standard Model of elementary particles. The Standard Model Higgs boson with a mass of 125 GeV decays most of the times to a pair of b-quarks. However, this decay is very difficult to study in a proton-proton collider like the LHC, due to the production of a huge background of b-jets (and also non-b-jets). In the LHC, the only production process with some chance to be used in this study is the associated production with a vector boson, which can decay leptonically allowing the identification of the event. One can use three possibilities: a Z boson decaying to neutrinos (0-lepton channel), a W boson decaying to an electron or muon and a neutrino (1-lepton channel) or a Z boson decaying to a pair of electrons or muons (2-lepton channel). The latter channel is the subject of this thesis. It is an interesting channel because the two charged leptons reduce the multi-jet background more than the other channels and because this channel reconstructs all the particles in the event. The analysis of the 2-lepton channel, known as ZH analysis, considers only events with high quality reconstructed particles. The two charged leptons are required to reconstruct the Z boson and the b-quarks which are reconstructed as jets, are required to be identified as b-jets (b-tagging) for the reconstruction of the Higgs boson. A statistical procedure uses the events selected as input to a likelihood fit to obtain normalisations of the simulated backgrounds from data and simulation comparisons and to extract the signal strength parameter, m, that multiplies the cross section times the branching ratio from the prediction for the Higgs boson from the Standard Model to adjust the ZH signal simulation process to the data. Both muons and electrons, used in the ZH analysis, are much better reconstructed than jets. So, most of the effort in this thesis was dedicated to the improvement of the jet reconstruction, in particular to the energy scale and uncertainty of the jets. I studied two methods to help reduce the systematic uncertainty of the jet energy scale, the leading experimental uncertainty of several physics analysis, with a important contribution to the ZH search, since the Higgs decays to b-quarks that hadronize into jets. First, I created a new trigger with the objective of selecting high-momenta isolated charged hadrons to be used in the determination of the calorimeter response to single hadrons, known as the single hadron response. In addition to extending the momentum range from 10 to 30 GeV, it did so in a high-pileup environment (pileup - number of interactions per proton bunch crossing). This contributed to the validation of the test beam determination of the jet energy scale uncertainty. For jets with pT above 1.8 TeV, for which the current in situ techniques are not able to set the jet energy scale uncertainty, the single hadron response is used to obtain this uncertainty. I have tested a new jet calibration in the ZH analysis: the global sequential calibration (GSC). This method was first developed to reduce the jet energy response dependence on the jet flavour, for gluon and light quark jets. My contribution was the validation and detailed performance studies for b-jets in general, and in particular for b-jets coming from the Higgs boson decay. This new calibration improved the jet energy response by about 2 - 3% and the jet energy resolution by about 20 %. Systematic uncertainties were evaluated for this calibration. I derived specific b-jet systematic uncertainties for this calibration as well as the uncertainties associated to differences between the ATLAS fast and full simulations. The Standard Model Higgs boson decaying in bb⁻ is expected to produce a very small excess of events in the invariant mass distribution of the two b-quarks. We need to have the best possible resolution on this variable and since GSC was found to reduce the b-jet jet energy response resolution, it was applied to the mb¯b distribution. GSC improves the invariant mass resolution up to 18 %. I performed the ZH analysis using a cut-based method and a statistical procedure to obtain the value of the signal strength parameter. A value of µ ⁼ ⁻ 0.69 ≠ 1.29.was obtained. This value is negative, but there is an enormous uncertainty, dominated by the statistical uncertainty, and the result is still compatible with the Standard Model prediction for the Higgs boson.
O mecanismo de quebra espontânea de simetria, que foi utilizado para explicar a massa das partículas elementares do Modelo Padrão, prevê a existência do bosão de Higgs. O bosão de Higgs foi apenas descoberto em 2012 pelas experiências ATLAS e CMS no LHC com uma massa de cerca de 125 GeV. Torna-se agora necessário estudar este novo bosão de modo a validar o Modelo Padrão das partículas elementares. O bosão de Higgs do Modelo Padrão, com uma massa de 125 GeV, vai decair para um par de quarks b na maioria das vezes. No entanto, este decaimento é bastante difícil de estudar num colisionador de protões como o LHC, devido ao enorme fundo de jatos b (e jatos em geral) que são produzidos. No LHC, o único processo de produção com alguma viabilidade para ser usado para estudar este decaimento é a produção associada a um bosão vetorial, que pode decair leptonicamente, proporcionando uma assinatura limpa para identificar o evento. Aqui existem três possibilidades: um bosão Z que decai para neutrinos (canal de 0 leptões), um bosão queWdecai para um eletrão ou um muão carregado e um neutrino (canal de 1 leptão), ou um bosão Z que decai para dois eletrões ou dois muões carregados (canal de 2 leptões). Este último canal foi o escolhido para esta tese. Neste canal a presença de dois leptões carregados reduz o fundo de multi-jatos mais de que nos outros canais e todas as partículas do acontecimento são reconstruidas. A análise do canal de dois leptões, referida como análise ZH, considera apenas acontecimentos com partículas reconstruidas de elevada qualidade. Aos dois leptões é exigido que reconstruam o bosão Z, e os quarks b, que são reconstruidos como jatos, têm de ser identificados como jatos b (b-tagging). Um processo estatístico utiliza os eventos candidatos num ajuste de verosimilhança (likelihood) para obter as normalizações dos fundos simulados e extrair o parâmetro de força do sinal, m, definido como o quociente entre o produto da seção eficaz e a razão de decaimento observados com respeito ao esperado no Modelo Padrão. Tanto os muões como os eletrões, utilizados na análise ZH, são muito melhor reconstruidos do que os jatos. Assim, o maior esforço desta tese concentrou-se para melhorar a reconstrução de jatos, em particular a escala de energia dos jatos e a sua incerteza. Estudei dois métodos que ajudaram a reduzir as incertezas sistemáticas da escala de incerteza dos jatos, que é a maior incerteza sistemática experimental de várias análises de pesquisa, com uma boa contribuição para análise ZH, uma vez que o bosão de Higgs decai para quarks b que hadronizam para jatos. Comecei por criar um novo mecanismo de seleção de acontecimentos (trigger) com o objetivo de escolher hadrões carregados isolados de elevado momento, que seriam utilizados na determinação da resposta em energia do calorímetro a hadrões isolados. Graças a este trigger, passou a ser possível utilizar hadrões isolados produzidos em colisões até um momento de 30 GeV/c, onde este limite era anteriormente de 10 GeV. Com esta amostra de hadrões isolados, pode calibrar-se a resposta do calorímetro em energia, obtendo-se simultaneamente um zona de validação da incerteza determinada para a escala de energia dos jatos hadrónicos a partir de um teste de feixe de partículas com energias bem definidas a partir de 20 GeV. O Trigger mostrou ainda a estabilidade da resposta num ambiente de elevado empilhamento de sinais (pileup - número de interações por colisão de pacotes de protões). Testei uma nova calibração da energia de jatos na análise ZH: a calibração sequencial global (GSC). Este método, foi em primeiro lugar, desenvolvido para reduzir a dependência da resposta em energia dos jatos no sabor dos mesmos (jatos de gluões ou de quarks leves). A minha contribuição foi a validação e o estudo detalhado do desempenho desta calibração para jatos b em geral, e em particular para jatos b provenientes do decaimento do bosão de Higgs. Esta nova calibração melhorou a resposta da energia dos jatos em 2 - 3% e a resolução em energia destes em 20 %. Avaliei os erros sistemáticos, derivei incertezas sistemáticas específicas para jatos b para esta calibração e ainda uma incerteza associada a diferenças entre simulação rápida e completa do detetor ATLAS. Espera-se que o bosão de Higgs do Modelo Padrão a decair em bb⁻ produza um pequeno excesso de eventos na distribuição de massa invariante do par de jatos b. Necessitamos obter a melhor resolução possível nesta variável e, como a calibração GSC mostrou reduzir a resolução em energia dos jatos b, a massa invariante foi também testada com GSC. A utilização desta nova calibração melhorou a resolução em massa até 18 %. Os estudos de validação e desempenho do GSC realizados permitiram a utilização desta calibração na análise do ZH. Desenvolvi uma análise ZH independente utilizando um método de cortes e procedimento estatístico. Obtive para o parâmetro força de sinal o valor µ ⁼ ⁻0.69 ≠ 1.29. Embora negativo, este valor possui uma enorme incerteza, dominada pela incerteza estatística, sendo o resultado ainda compatível com a previsão para o bosão de Higgs feita pelo Modelo Padrão.
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Pedro, Rute Costa Batalha 1984. "Search for the higgs boson at ATLAS/LHC in WH associated production and decay to b-quark pairs." Doctoral thesis, 2017. http://hdl.handle.net/10451/34140.
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Tese de doutoramento, Física, Universidade de Lisboa, Faculdade de Ciências, 2017The Higgs mechanism was incorporated in the Standard Model of elementary particles and interactions in the 1960’s to solve the existent conflict between massive particles and conservation laws of particle physics. A consequence of this mechanism is the prediction of a new fundamental particle, the Higgs boson, observed for the first time in 2012 by the ATLAS and CMS experiments at the Large Hadron Collider. This thesis describes the search for the Higgs decay into a pair of bquarks with the ATLAS experiment, using pp collision events with an 8 TeV center-of-mass energy provided by the LHC in 2012. Although the branching fraction of the H → bb⁻ decay is dominant (BR(H→ bb⁻ ) =57.7% for mH = 125 GeV), this decay mode was not yet observed. The search is particularly challenging given the huge amount of background events containing jets. To reduce this background, the Higgs production associated with aW=Z boson is usually explored, as the leptons resulting from the W=Z decay can effectively trigger the signal. The W associated production with the W boson decaying leptonically is considered. The data analysis searches for events compatible with the W H → lv bb⁻ signal topology: one electron or muon, missing transverse energy associated with the undetected neutrino and two jets resulting from b - quark fragmentation. Events containing jets and charged leptons, as topquark production andW+jets, are the main backgrounds of the analysis. Since their production cross-section is much larger than the signal cross-section, the resulting signal-to-background proportion, (B) S/ √B only 0.3. The analysis comprehends a Multivariate technique, Boosted Decision Tree (BDT), to exploit correlations in the event observables aiming at increasing the sensitivity to the signal. A study that resulted in a 12% gain in the BDT performance was carried on. Samples of signal and background simulated in the same conditions as data are also analysed. Given the small S=pB, it was indispensable to verify that the simulation models correctly the background processes, and to evaluate the systematical uncertainties associated with their prediction. In this context, a study to determine the systematic uncertainties of the single top background modelling was conducted. The ratio between the observed signal event rate and the Standard Model prediction was 1:65⁺0:58 ₋0:56(stat) ⁺0:58 ₋0:48(syst) = 1:65 ⁺0:82₋0:74, and therefore the measurement is compatible with the SM prediction within uncertainties. The signal significance, representing the compatibility between the data observation and the background-only hypothesis, corresponds to the gaussian probability of observing a value larger than 2.02 standard deviations and is not sufficient to state the observation of the W H → lv bb⁻ process.
O mecanismo de Higgs foi introduzido no Modelo Padrão das partículas elementares e suas interacção¸ na década de 1960, para resolver o conflito existente entre partículas massivas e leis de conservação da física de partículas. Uma das consequências deste mecanismo ´e a previsão de uma nova partícula fundamental, o bosão de Higgs, observado pela primeira vez em 2012 pelas experiencias ATLAS e CMS do LHC/CERN. Esta tese descreve a pesquisa pelo bosão de Higgs através do seu decaimento em pares de quarks b com o detector ATLAS, usando acontecimentos de colisões pp com uma energia de centro-de-massa de 8 TeV. Este modo de decaimento ainda não foi observado, embora a razão de bifurcação (BR) seja dominante relativamente aos processos alternativos: para um Higgs de massa mH = 125 GeV, BR(H → lv bb⁻) =57.7%. A sua procura ´e desafiante e difícil devido à quantidade de acontecimentos de fundo com jactos de partículas. Para reduzir esse fundo, escolhe-se a produção do bosão de Higgs associada a um bosão W=Z, uma vez que os leptões resultantes do decaimento do W=Z constituem uma forma efectiva de identificar o sinal. Considera-se a produção associada a umW e seleccionam-se os acontecimentos de acordo com a topologia do sinal W H → lv bb⁻ : um electrão ou um muão, energia em falta associada ao neutrino e dois jactos resultantes da fragmentação dos quarks b. Acontecimentos que resultam em jactos e leptões carregados, como a produção¸ de quarks top e de W+jactos, constituem os fundos principais da análise. Como a seccão eficaz de produção¸ ˜ao destes processos ´e muito superior à do sinal, a proporção de acontecimentos de sinal (S) e fundo (B) S/ √B e de apenas 0.3. A análise usa uma t´técnica Multivariacional, que explora correlações entre diferentes observáveis através do método Boosted Decision Tree (BDT), para aumentar a sensibilidade aos acontecimentos de sinal. Realizou-se um estudo que permitiu melhorar o desempenho da BDT até 12%. São também analisadas amostras de simulação de sinal e fundos nas mesmas condicões. Dada a pequena significância do sinal relativamente ao fundo, foi indispensável verificar que a simulação modela correctamente os fundos e avaliar as incertezas sistemáticas na sua previsão. Neste contexto, foi efectuado um estudo que levou `a determinação das incertezas sistemáticas associadas `a modelação da produção¸ do quark top. A razão entre a taxa de acontecimentos de sinal observada e a prevista pelo Modelo Padrão foi 1:65⁺0:58 ₋0:56(stat) ⁺0:58 ₋0:48(syst) = 1:65 ⁺0:82, medida compatível com a previsão tendo em conta as incertezas obtidas. A significância do sinal medido, que representa a probabilidade dos dados observados serem compatíveis com a hipótese de ausência de sinal, corresponde `a probabilidade gaussiana de observar um valor superior a 2.02 desvios padrão e ´e insuficiente para se declarar a observação do processo W H → lv bb⁻.
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Brelier, Bertrand. "Étude de la production associée ZH/WH, H - ±gamma gamma» avec le détecteur ATLAS." Thèse, 2008. http://hdl.handle.net/1866/6407.
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Coelho, Luis Felipe Falda de Ulhoa. "Study of the CP nature of the top-Higgs coupling in ttH production at the LHC." Master's thesis, 2020. http://hdl.handle.net/10316/92144.
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Dissertação de Mestrado em Física apresentada à Faculdade de Ciências e TecnologiaNo Modelo Padrão (SM), é previsto que o bosão de Higgs seja uma partícula escalar e que suas interações não violem a simetria CP. Após a observação da produção do bosão de Higgs em associação com um par de quarks top (ttH) pelas experiências ATLAS e CMS em 2018, a observação de uma componente ímpar à transformações de carga-paridade (CP) em um dos acoplamentos do bosão de Higgs constituiria uma importante descoberta de física além do SM (BSM). Recentemente, ATLAS e CMS procuraram essa componente em eventos ttH com o Higgs decaindo em dois fotões. No entanto, o acoplamento entre o Higgs e os fotões é induzido por loops e pode ser afetado por efeitos da nova física. Esta tese descreve o estudo da natureza CP do acoplamento de Yukawa do Higgs aos quarks top por meio da análise de eventos ttH no canal de decaimento H→bb, e fornece projeções deste estudo do Run 2 do Large Hadron Collider (LHC) ao LHC de alta luminosidade (HL-LHC). A análise usa dados de colisão protão-protão coletados com o detector ATLAS durante o período do Run 2 do Grande Colisor de Hadrões (LHC) com uma energia de centro de massa de √s=13 TeV e luminosidade integrada total de 139 fb-1. São usados apenas eventos contendo um ou dois leptões no estado final do decaimento do par de quarks top. Em seguida, os eventos são classificados em regiões de acordo com o número de jatos e o número de b-jatos marcados usando ponto de operação (WPs) de 60% and 70%. Várias técnicas multivariadas foram usadas para melhorar a sensibilidade da análise, uma árvore da decisão reforçada (BDT) foi treinada para separar o sinal do fundo e outra para distinguir entre diferentes cenários de CP. Variáveis sensíveis ao CP, incluindo observáveis calculadas no referencial de laboratório e variáveis angulares calculadas em referenciais específicos, foram usadas no ajuste e no treinamento das BDTs.Um ajuste de verossimilhança é executado em todas as regiões de análise para restringir as previsões de fundo e reduzir as incertezas sistemáticas. O valor esperado para o ângulo de mistura CP é obtido desse ajuste. Além disso, uma extrapolação da análise foi realizada nesta tese, a fim de fornecer projeções sobre a medição do ângulo de mistura de CP para o LHC de alta luminosidade (HL-LHC). Foram considerados diferentes cenários para a evolução das incertezas sistemáticas com o aumento esperado da luminosidade. O valor esperado para o ângulo de mistura de CP foi obtido para vários valores diferentes de luminosidade até 3000 fb-1. Com as atuais incertezas sistemáticas, espera-se que a produção de ttH pura CP-ímpar seja excluída com 99.73\% de nível de confiança (CL) apenas no final do projeto HL-LHC. A significância de exclusão CP-ímpar é representada em função da luminosidade para cada um dos cenários considerados, e os efeitos dos vários tipos de incertezas são avaliados.
In the Standard Model (SM), the Higgs boson is predicted to be a scalar particle with no CP-violating interactions. After the observation of the Higgs boson production in association with a top quark pair (ttH) by ATLAS and CMS in 2018, the measurement of an odd charge-parity (CP) component in one of the Higgs boson couplings would constitute an important discovery of physics beyond the SM (BSM). Recently, ATLAS and CMS searched for such a component in ttH events with the Higgs decaying into two photons. However, the coupling between the Higgs and the photons is loop-induced and could be modified by effects of new physics. This thesis describes the study of the CP nature of the Higgs Yukawa coupling to the top quarks by analyzing ttH events in the H→bb decay channel, and provides projections of this search from the Large Hadron Collider (LHC) Run 2 to the High-Luminosity LHC (HL-LHC). The analysis uses the full Run 2 dataset of proton-proton collision collected with the ATLAS detector at a center-of-mass energy of √s=13 TeV and total integrated luminosity of 139 fb-1. Only events containing either one or two leptons in the final state from the decay of the top quark pair are used in the analysis. Then, the events are classified into regions according to the number of jets and the number of b-tagged jets using the 60% and 70% working points (WPs). Two sets of multivariate classifiers are utilized to improve the analysis sensitivity. One classifier targets the classification of signal against backgrounds and the other targets the separation between different CP scenarios. Several CP sensitive variables, including lab-frame observables and angular variables calculated in specific frames, were used in the training of the BDTs. A profile likelihood fit is performed over all analysis regions to constrain the background predictions and reduce the systematic uncertainties. The expected value for the CP-mixing angle is presented. An extrapolation of the analysis is performed in order to provide projections on the measurement of the CP-mixing angle for the HL-LHC. Different scenarios for the evolution of the systematic uncertainties with the expected increase in the luminosity were considered. The expected value for the CP-mixing angle was obtained for several different values of luminosity up to 3000 fb-1. With the current systematic uncertainties, the pure CP-odd ttH production is expected to be excluded with 99.73% confidence level (CL) only at the end of the HL-LHC project. The CP-odd exclusion significance is represented as a function of the luminosity for each of the scenarios considered, and the effects of the various types of uncertainties are evaluated.
Outro - FCT CERN/FIS-PAR/0002/2019
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Fugel, Frank [Verfasser]. "Associated production of higgs bosons and heavy quarks in two photon collisions at next-to-leading order / vorgelegt von Frank Fugel." 2007. http://d-nb.info/986396370/34.
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Warsinsky, Markus [Verfasser]. "Studies of b-associated production and muonic decays of neutral Higgs bosons at the ATLAS experiment within the minimal supersymmetric standard model / von Markus Warsinsky." 2008. http://d-nb.info/990711161/34.
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