Dissertations / Theses on the topic 'Higgs boson physics'
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1
Quevillon, Jérémie. "Higgs Physics Beyond the Standard Model." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01070196.
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On the 4th of July 2012, the discovery of a new scalar particle with a mass of order 125 GeV was announced by the ATLAS and CMS collaborations. An important era is now opening: the precise determination of the properties of the produced particle. This is of extreme importance in order to establish that this particle is indeed the relic of the mechanism responsible for the electroweak symmetry breaking and to pin down effects of new physics if additional ingredients beyond those of the Standard Model are involved in the symmetry breaking mechanism. In this thesis we have tried to understand and characterize to which extent this new scalar field is the Standard Model Higgs Boson and set the implications of this discovery in the context of Supersymmetric theories and dark matter models.In a first part devoted to the Standard Model of particle physics, we discuss the Higgs pair production processes at the LHC and the main output of our results is that they al-low for the determination of the trilinear Higgs self-coupling which represents a first important step towards the reconstruction of the Higgs potential and thus the final verifica-tion of the Higgs mechanism as the origin of electroweak symmetry breaking.The second part is about Supersymmetric theories. After a review of the topics one of our result is to set strong restrictions on Supersymmetric models after the Higgs discov-ery. We also introduce a new approach which would allow experimentalists to efficiently look for supersymmetric heavy Higgs bosons at current and next LHC runs.The third part concerns dark matter. We present results which give strong constraints on Higgs-portal models. We finally discuss alternative non-thermal dark matter scenario. Firstly, we demonstrate that there exists a tight link between the reheating temperature and the scheme of the Standard Model gauge group breaking and secondly we study the genesis of dark matter by a Z' portal.
2
Xie, Si Ph D. Massachusetts Institute of Technology. "Search for the Standard Model Higgs boson decaying to two W bosons at CMS." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/77499.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 255-264).
In this thesis, we search for the production of the Standard Model Higgs boson at the Large Hadron Collider, through its decay mode to two W bosons, which each in turn decay into a charged lepton and a neutrino. The Higgs boson is the only elementary particle predicted by the Standard Model of particle physics which has not yet been experimentally observed. The question of its existence has been the subject of a wide body of experimental and theoretical work for the past half-century. Using 4.9 fb-1 of integrated luminosity, this search is expected, on average, to exclude the Standard Model predicted Higgs boson production cross section for masses between 126 GeV/c 2 and 260 GeV/c 2 under the background-only hypothesis. We observe no statistically significant excesses in the data, and we exclude the Standard Model Higgs boson production for masses between 129 GeV/c 2 and 260 GeV/c 2 . This result represents a significant reduction of the mass region in which the Standard Model Higgs boson is allowed to exist.
by Si Xie.
Ph.D.
3
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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Rankin, Dylan Sheldon. "Exclusive search for Higgs boson to gamma-gamma decay via vector boson fusion production mechanism." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78498.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 39-40).
We perform an exclusive search for the Higgs boson to gamma-gamma decay via vector boson fusion. We utilize the characteristic features of vector boson fusion, such as the di-jet [Delta][eta] and mass, as well as the di-photon [rho][tao], to search for the Higgs boson to gamma-gamma decay via the vector boson fusion process. The theoretical production cross section limit is analyzed over the accepted possible mass range for the Higgs boson, 120-130 GeV/c 2 . We are able to reduce the theoretical production cross section limit to ~ 6[sigma]SM in this range by using a boosted decision tree. Comparison to the cut based approach used by the CMS Collaboration shows no improvement in using a BDT as opposed to a cut based approach.
by Dylan Sheldon Rankin.
S.B.
5
Braathen, Johannes. "Automating Higgs precision calculations." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS073/document.
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L’étude des propriétés du boson de Higgs représente une excellente opportunité pour la recherche de Nouvelle Physique. En particulier, sa masse est mesurée avec une précision impressionnante, de l’ordre de 0.1%, tandis qu’elle est aussi prédite par certains modèles au-delà du Modèle Standard, notamment les modèles supersymétriques. Le but de cette thèse est de faire avancer le calcul des corrections radiatives aux masses des scalaires dans les modèles au-delà du Modèle Standard, ainsi que l’automatisation de ces calculs, afin d’établir ou d’améliorer les limites sur les couplages entre la Nouvelle Physique et le boson de Higgs. Nous calculons d’abord les corrections dominantes à deux boucles, de la forme O(alpha_s alpha_t), aux masses des scalaires neutres dans les modèles supersymétriques à jauginos de Dirac. Ensuite, nous montrons comment surmonter la Catastrophe des Bosons de Goldstone, un cas de divergences infrarouges dues aux bosons de Goldstones de masses nulles qui affecte les calculs de potentiels effectifs, d’équations « tadpoles » et d’énergies propres, en adoptant un schéma de renormalisation « on-shell » pour les masses des bosons de Goldstone. Nous illustrons la mise en œuvre numérique de notre solution dans le programme SARAH, et finalement, nous considérons le comportement aux hautes énergies de modèles non-supersymétriques avec des secteurs scalaires étendusThe Standard Model-like Higgs boson provides an excellent setting for the indirect search of New Physics, through the study of its properties. In particular its mass is now measured with an astonishing precision, of the order of 0.1%, while being predicted in some models of Beyond the Standard Model (BSM) Physics, such as supersymmetric (SUSY) models. The main purpose of this thesis is to push further the calculation of radiative corrections to Higgs boson masses in BSM models, as well as the automation of these calculations, in order to set or improve constraints on New Physics coupling to the Higgs boson. A first chapter is devoted to the computation of the leading two-loop O (alpha_s alpha_t) corrections to neutral scalar masses in SUSY models with Dirac gauginos. Then, we show to address the Goldstone Boson Catastrophe -- a case of infra-red divergences due to massless Goldstone bosons that plague the calculation of effective potentials, tadpole equations, and self-energies -- in the context of general renormalisable field theories, by adopting an on-shell renormalisation scheme for the Goldstone masses. Afterwards, we illustrate the numerical implementation of our solution to the Goldstone Boson Catastrophe in the public tool SARAH. Finally, in a last chapter, we consider the high-scale behaviour of non-supersymmetric models with extended Higgs sectors
6
Mudd, Richard David. "Experimental study of the properties of the Higgs boson." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/6761/.
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Measurements of Higgs boson production and decay rates are presented using the proton-proton collision data collected by the ATLAS experiment during LHC Run I, corresponding to 4.5 fb\(^-\)\(^1\) at 7 TeV and 20.3 fb\(^-\)\(^1\) at 8 TeV. Under certain assumptions, the coupling strengths of the Higgs boson to Standard Model particles are also probed. The H -> ZZ\(^(\)\(^*\)\(^)\)\(_-\)\(_>\) 4I final state, where I = e, mu, is discussed, and is observed with a significance corresponding to 8.1 standard deviations. The Higgs boson production rate, relative to the Standard Model prediction, is measured to be mu = 1.44\(^+\)\(^0\)\(^.\)\(^4\)\(^0\)\(_-\)\(_0\)\(_.\)\(_3\)\(_3\) at the ATLAS best-fit value for the measurement of the Higgs boson mass, m\(_H\) = 125.36 GeV. The various Higgs boson production and decay modes studied by the ATLAS experiment are also combined. The couplings of the Higgs boson are probed in a number of benchmark models, where a good agreement with the Standard Model prediction is observed for each model considered. The Higgs boson coupling measurements are also used to place constraints on a number of beyond the Standard Model theories, and are combined with direct searches for invisible Higgs boson decays to place a limit on the Higgs boson branching ratio to invisible final states.
7
Romero, Daniela. "Simulation of Higgs boson pair production in Vector Boson Fusion at the LHC." Thesis, Uppsala universitet, Högenergifysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-433554.
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MadGraph5 is used to generate events with Higgs boson pairs from vector boson fusion (VBF) at leading-order (LO) and next-to-leading-order (NLO) accuracy in QCD. The simulations are used to compute fiducial cross-sections in proton-proton collisions at a centre-of-mass energy of 13 TeV, using several kinematic cuts on the outgoing jets, e.g. the jet transverse momenta and pseudorapidity. The resulting cross-sections for NLO and LO are compared and their ratio, the K-factor, is calculated for every kinematic cut. An attempt is made to extend the NLO simulation for non-Standard Model (SM) couplings between two vector bosons and two Higgs bosons (VVHH), however the corresponding model was found to be only compatible with LO accuracy in QCD.
8
Dominguez, Patricia Zoila. "Search for Higgs to invisible decays in vector boson fusion production." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/111886.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 51-52).
A search for invisibly decaying Higgs bosons is performed using the vector boson fusion production (VBF) mode. This search was conducted using Run 2 data, collected by the CMS detector at the LHC in 2016 at a center of mass energy of 13 TeV, corresponding to an integrated luminosity of 5.9 fb-1. The control regions for the signal, invisibly decaying VBF Higgs bosons, are estimated using a cut-based selection strategy adapted from prior analyses. Selection criteria for the signal is applied as well. Assuming standard model Higgs boson cross sections and acceptances, the observed (expected) upper limit on the signal strength of VBF Higgs bosons invisibly decaying at mH = 125 GeV is found to be r < 54.7 (51.8) at a 95% confidence level
by Patricia Zoila Dominguez.
S.B.
9
Bertolini, Daniele Ph D. Massachusetts Institute of Technology. "Electroweak symmetry breaking in the era of the Higgs boson discovery." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91079.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014.166
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 115-125).
In this thesis we study possible deviations from the electroweak symmetry breaking mechanism as predicted by the Standard Model (SM), and we introduce a new framework to analyze hadronic final states at colliders. In the first part, we begin by considering supersymmetric extensions of the SM and by studying the connection between electroweak symmetry breaking and supersymmetry breaking. Contrary to the common lore, we show that a visible dynamics in the Higgs sector can contribute to supersymmetry breaking, as long as soft masses receive contributions also from one or more hidden sectors. A striking feature is the presence of a light pseudo-goldstino in the spectrum. We study potential collider signatures of visible supersymmetry breaking in Higgs and neutralino decays. Then, we move to a study of the Higgs data collected at the Large Hadron Collider (LHC). By using both measurements of the Higgs boson couplings, and limits on Higgs-like states at higher masses, we investigate whether the data support the possibility that the SM Higgs is mixed with another scalar. We consider fits to simplified models and we find that mixing angles with sin 2 6 > 0.2 are disfavored at 95% CL over a scalar mass range 200 - 1000 GeV. In the second part, we propose a new way to define inclusive jet (and subject) based observables at colliders. We introduce a new class of event shapes that characterize the jet-like structure of the event by using only information in the neighborhood of each particle. We show that conventional jet-based observables such as jet multiplicity, summed scalar transverse momentum, and missing transverse momentum can be recovered within this approach. We show that in this framework trimming can be recast as a particle weight assignment, without explicit jet identification. Finally, we comment on potential applications of the method both at trigger and analysis level.
by Daniele Bertolini.
Ph. D.
10
Dominguez, Patricia Zoila. "Search for Higgs to invisible decays in vector boson fusion production." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111886.
Full textAbstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 51-52).
A search for invisibly decaying Higgs bosons is performed using the vector boson fusion production (VBF) mode. This search was conducted using Run 2 data, collected by the CMS detector at the LHC in 2016 at a center of mass energy of 13 TeV, corresponding to an integrated luminosity of 5.9 fb-1. The control regions for the signal, invisibly decaying VBF Higgs bosons, are estimated using a cut-based selection strategy adapted from prior analyses. Selection criteria for the signal is applied as well. Assuming standard model Higgs boson cross sections and acceptances, the observed (expected) upper limit on the signal strength of VBF Higgs bosons invisibly decaying at mH = 125 GeV is found to be r < 54.7 (51.8) at a 95% confidence level
by Patricia Zoila Dominguez.
S.B.
11
Tiesi, Alessandro. "Higgs boson masses in a non-minimal supersymmetric model." Thesis, University of Glasgow, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249922.
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Dreyer, Frédéric. "Precision physics at the large hadron collider." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066170/document.
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L'avènement du LHC marque le début d'une ère de haute précision en physique des particules. Dans cette thèse de doctorat, nous abordons avec des outils innovants deux processus clés des collisionneurs de hadrons: la production inclusive de jets, et la production du boson de Higgs par fusion de bosons vecteurs (VBF). Dans la première partie de cette thèse, nous montrons comment resommer les premiers ordres logarithmiques de rayon de jet R, et appliquons ce formalisme à une étude approfondie du spectre inclusif des jets. Nous étudions les termes dépendant de R au troisième ordre non-nul (next-to-next-to-leading-order, NNLO), et les intégrons dans notre calcul. Nous examinons les éliminations dans la dépendance d'échelle, conduisant à une nouvelle prescription pour l'évaluation des incertitudes, et vérifions l'impact d'effets non-perturbatifs. Dans la deuxième partie de cette thèse, nous étudions les corrections de chromodynamique quantique dans la production de Higgs par VBF. En utilisant l'approche des fonctions de structure, nous calculons les corrections de quatrième ordre non-nul (NNNLO) à la section efficace inclusive. Nous calculons ensuite les corrections NNLO entièrement différentielles à la production de Higgs par VBF. Nous montrons que ces contributions sont significatives après coupures VBF, se trouvant en dehors des bandes d'incertitude d'échelle NLOWith the advent of the LHC, particle physics has entered an era where high precision is required. In this thesis, we tackle two of the key processes at hadron colliders using innovative tools: inclusive jet production and Higgs production through vector-boson fusion (VBF). In the first part of this thesis, we show how to resum leading logarithmic terms of the jet radius R, and apply this formalism to a detailed study of the inclusive jet spectrum. We study subleading R-dependent terms at next-to-next-to-leading order (NNLO), and incorporate them into our calculation. We investigate cancellations in the scale dependence, leading to new prescriptions for evaluating uncertainties, and examine the impact of non-perturbative effects. In the second part of the thesis, we study QCD corrections in VBF-induced Higgs production. Using the structure function approach, we compute the next-to-next-to-next-to-leading order (NNNLO) corrections to the inclusive cross section. We then calculate the fully differential NNLO corrections to VBF Higgs production. We show that these contributions are substantial after VBF cuts, lying outside the NLO scale uncertainty bands
13
Fleischhack, Henrike. "Studies of the Phenomenology of H+ → W+Z events with ATLAS at LHC." Thesis, Uppsala universitet, Högenergifysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-175066.
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The Higgs sector is the last part of the standard model of particle physics where we lack directexperimental results. Many extensions to the standard model describe an extended Higgs sector,often containing charged scalar bosons in addition to the standard model’s neutral Higgs boson.The H+WZ vertex can be used to distinguish between different non-standard Higgs sectors, andto measure the mass of the charged Higgs boson. In this report I will examine a promising searchchannels at the LHC and look at its phenomenology using monte carlo simulations.
14
Trifis, Omran. "Search for a light charged Higgs boson in the decay channel H^+ --> c¯s using the ATLAS detector." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/search-for-a-light-charged-higgs-boson-in-the-decay-channel-h--cs-using-the-atlas-detector(27e6a49c-a45c-4bbb-8965-708921b53cb8).html.
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A search for a light charged Higgs boson (H^±) decaying into two jets (c¯s) using pp collisions at s = sqrt(7 TeV) is presented. A data sample corresponding to an integrated luminosity of 4.7 fb^−1 recorded by the ATLAS detector in 2011 has been analysed. The search is performed in the semi-leptonic t¯t channel, where one of the top quarks decays via t --> bH^±. The other top quark decays to bW, where the W boson decays to a lepton (e/μ) and a neutrino. The search is based on the invariant mass distribution of the two light jets in the final state as the discriminating variable. With no observation of an H^± signal, 95% confidence level(CL) upper limits are set on the decay branching ratio of top quarks to charged Higgs bosons. These limits are between 5% and 1% for charged Higgs boson masses between 90 and 150 GeV, and can be considered as model-independent limits on the decay branching ratio of top quarks to any charged boson beyond the Standard Model.
15
Hallberg, Jesper. "Study of charged Higgs bosons using multi-jet final states with the ATLAS experiment at the LHC." Thesis, Uppsala universitet, Högenergifysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-227536.
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The ATLAS experiment at the LHC is searching for evidence of charged Higgs bosons, without yet finding it. This report investigates the possibility of reconstructing charged Higgs bosons using multi-jet final states (pp -> [b]tH+ -> [b]bbbql\nu) with focus on fully hadronic H^+ -> hW decays using a simulation of 500k events with m_{H+} = 250 GeV. After optimizing TMVA (Toolkit for Multivariate Analysis) input variables for BDT (Boosted Decision Trees), the mass of H+ was recreated with an efficiency of up to 26,7% (correct combinations).
16
Lazovich, Tomo. "Observation of the Higgs boson in the WW* channel and search for Higgs boson pair production in the bb̄bb̄ channel with the ATLAS detector." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493490.
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This dissertation presents the observation and measurement of the Higgs boson in the H→ WW*→ ℓνℓν channel at √s = 7 TeV and √s = 8 TeV and a search for Higgs pair production in the HH→ bb̄bb̄ channel at √s = 13 TeV with the ATLAS detector in pp collisions at the Large Hadron Collider.
First, the discovery of a particle consistent with the Higgs boson in 4.8 fb−1 at √s = 7 TeV and 5.8 fb−1 at √s = 8 TeV is discussed. Then, the measurement of the Higgs boson signal strength and cross section in both the gluon fusion and vector boson fusion (VBF) production modes using 20.3 fb−1 of √s = 8 TeV data combined with 4.8 fb−1 of 7 TeV data is shown. The combined signal strength is measured to be µ = 1.09−0.21+0.23. The total observed significance of the H → WW∗ process is observed to be 6.1σ (with 5.8 σ expected). Advanced methods for background reduction and estimation, particularly in same-flavor lepton final states, are shown. The VBF signal strength is measured to be µVBF = 1.27−0.45+0.53 with an observed significance of 3.2σ (with 2.7 σ expected). In the VBF channel, a selection requirement based method, the precursor to the final multivariate technique used for the result, is detailed.
Finally, a search for Higgs pair production in the bb̄bb̄ final state with 3.2 fb−1 at √s = 13 TeV is presented. A particular focus is placed on a tailored signal region for resonant production of Higgs pairs at high masses. No significant excesses are observed, and upper limits on cross sections are placed for spin-2 Randall Sundrum gravitons (RSG) and narrow spin zero resonances. The cross section of σ(pp → GKK* → hh → bbbb) with k/MPl=1 is constrained to be less than 70 fb for masses in the range 600 < mGKK* < 3000 GeV. The cross section upper limits for σ(pp → H → hh → bbbb) range from 30 to 300 fb in the mass range of 500 < mH < 3000 GeV.Physics
17
Wright, Michael. "Higgs production in association with a Z boson at the LHC." Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5754/.
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The associated Z vector boson production rate of the Standard Model Higgs boson has been measured in decays into two b quarks, with the Z boson decaying into an electron or muon pair in the ATLAS detector at the Large Hadron Collider (LHC). The associated Z vector boson production cross section in the Standard Model is almost two orders of magnitude smaller than the dominant Higgs boson production cross section from gluon fusion. Proton-proton collision data at a centre-of-mass energy of 8 TeV delivered by the LHC with the ATLAS detector corresponding to an integrated luminosity of 13 fb−1 has been analysed. A Higgs boson produced via associated production with a Z vector boson is excluded with a 95% confidence level in a mass range between 110 to 130 GeV at 6 to 11 times the Standard Model cross section, respectively.
18
Singh, Kevin. "Search for the standard model Higgs Boson in the Z gamma channel." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83798.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 93-94).
The Higgs decay into a photon and a Z boson, with the Z boson decaying into an electron-positron pair (electron channel) or muon-antimuon pair (muon channel), allows for accurate reconstructions of the Higgs boson mass and measurement of the Higgs to Z-[gamma] coupling. We explore selection criteria for the photon and the two leptons and provide preliminary observed and expected limits for the Higgs boson production cross section in the mass range from 120 GeV to 150 GeV. The data used in this analysis was collected with the CMS detector and corresponds to 5 fb- 1 and 19 fb-1 at center-of-mass energies of 7 TeV and 8 TeV, respectively.
by Kevin Singh.
S.B.
19
Dutta, Valentina. "Evidence for a Higgs boson in tau decays with the CMS detector." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91392.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014.120
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 175-185).
In this thesis, I describe the search for a Higgs boson through its decay to a pair of tan leptons with the tau-pair subsequently decaying to ail electron, a muon, and neutrinos. The search is performed using data collected from proton-proton collisions by the Compact Muon Solenoid experiment at the Large Hadron Collider, corresponding to 5.0 fb-1 of integrated luminosity recorded at a center-of-mass energy of 7 TeV and 19.7 fb-1 at 8 TeV. The expected significance for a Standard Model Higgs boson signal with a mass of 125 GeV is at the level of 1.2 standard deviations for the electron muon tau-pair decay mode. A mild excess of events is seen above the SM background expectation in this decay mode, consistent with a SM Higgs boson of mass 125 GeV. In combination with results using other tau-pair decay modes, an excess of events above the background expectation is seen at the level of 3.4 standard deviations. This constitutes the first evidence for a Higgs boson to decay to leptons. This thesis also describes an analysis of the data in the context of physics beyond the Standard Model, particularly in the framework of its Minimal Supersymnnetric extension.
by Valentina Dutta.
Ph. D.
20
Koletsou, Iro. "Recherche du boson de Higgs dans le canal diphoton au LHC avec le détecteur ATLAS." Phd thesis, Université Paris Sud - Paris XI, 2008. http://tel.archives-ouvertes.fr/tel-00293103.
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Cette thèse a comme but la préparation à la recherche du boson de Higgs dans le canal diphoton au LHC, avec le détecteur ATLAS. Les problématiques qui sont étudiées s'articulent autour de la reconstruction du vertex H en deux photons, avec l'aide du calorimètre électromagnétique et du détecteur interne, et de la résolution en masse invariante diphoton.
Des simulations différentes du détecteur ATLAS et les effets de la quantité de matière et des désalignements ont été étudiés. Des problématiques de calcul de la signification statistique ont également été discutées et le potentiel de découverte pour une basse luminosité integrée a été évalué.
Une partie de la thèse se place dans le cadre des données CSC qui utilisent la plus récente simulation du détecteur ainsi que des méthodes de reconstruction mises au point et qui servent à effectuer une mise à jour de l'analyse effectuée par ATLAS. Toutes les étapes du traîtement du signal et du bruit de fond ont été discutées. Finalement on s'attend à voir un signal de 3 sigma avec une luminosité integrée de 10 fb-1
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Sung, Kevin Kai Hong. "Search for the Higgs Boson in the ZZ --> ℓℓvv channel with CMS." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83819.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 171-176).
The Standard Model (SM) of particle physics is a quantum field theory of the strong, weak, and electromagnetic interactions. It successfully describes a large majority of observed phenomena at microscopic scales. The key issue that remains to be addressed is the mechanism for electroweak symmetry breaking (EWSB). Without EWSB in the theory, the massive weak force mediators - the W and Z bosons, are required to be massless to satisfy gauge symmetry. To incorporate EWSB into the SM, the Higgs mechanism is invoked and introduces a scalar field, the Higgs field, that couples to the W and Z bosons and gives them mass. Additionally, the SM postulates that the fundamental fermions acquire mass through interactions with the Higgs field. Observation of the field quantum, the Higgs boson, would greatly validate our ideas on electroweak symmetry breaking and complete the table of fundamental particles predicted by the Standard Model. If it exists, the Higgs boson has eluded detection for decades. A primary objective of the Large Hadron Collider (LHC) project is to make a definitive statement about the existence of the Higgs boson. The LHC provided proton-proton collisions at [square root of]s = 7 TeV for the 2011 run. The search for the SM Higgs with the 2011 dataset represented the first major foray into the search effort by the LHC project. This thesis presents a search for the SM Higgs boson in the ZZ -->2ℓ2v channel from the analysis of 4.9 fb-1 of data collected with the Compact Muon Solenoid (CMS) detector at the LHC. Overviews of electroweak theory and of Higgs production at the LHC are given, followed by descriptions of the CMS detector and the algorithms for event reconstruction. A measurement of the inclusive cross section for Z boson production is presented as a validation on the measured efficiencies of the electron and muon reconstruction and selection requirements. Lastly, the Higgs search analysis and results are presented.
by Kevin Kai Hong Sung.
Ph.D.
22
Chan, Matthew Hans. "Search for the Higgs boson in its decay into tau leptons at CMS." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/84396.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 199-204).
A search for the Standard Model Higgs boson in the H --> rr channel is presented. The search is performed on proton collision data collected by the Compact Muon Solenoid at the Large Hadron Collider. The data corresponds to 4.9 fb-1 of proton collisions at [square root of]s = 7 TeV and 19.5 fb-1 at [square root of]s = 8 TeV. The search is based on di-tau events in which one tau decays into an electron or muon, and the other tau decays into hadrons. The search focuses on Higgs masses between 110 GeV and 145 GeV. The analysis reveals no statistically significant excess in the data over the Standard Model backgrounds. Upper limits on the Higgs production cross section at the 95% confidence level are established. The observed limit is statistically consistent with the expected limit in the background-only hypothesis but does not exclude any Higgs mass.
by Matthew Hans Chan.
Ph.D.
23
Hall, David Christopher. "Discovery and measurement of the Higgs boson in the WW decay channel." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:8ba0b59b-8673-44ac-bccf-c5eae91fac9a.
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In the Standard Model of particle physics, the non-zero masses of the W and Z bosons and the fermions are generated through interactions with the Higgs field, excitations of which correspond to Higgs bosons. Thus, the experimental discovery of the Higgs boson is of prime importance to physics, and would confirm our understanding of fundamental mass generation. This thesis describes a search for the gg → H → WW → lνlν process of Higgs boson production and decay. It uses the LHC Run I dataset of pp collisions recorded by the ATLAS detector, which corresponds to an integrated luminosity of 4.5 fb−1 at √s = 7 TeV and 20.3 fb−1 at √s = 8 TeV. An excess of events is observed with a significance of 4.8 standard deviations, which is consistent with Higgs boson production. The significance is extended to 6.1 standard deviations when the vector boson fusion production process is included. The measured signal strength is 1.11+0.23-0.21 at mH = 125 GeV. A cross section measurement of WW production, a major background to this search, is also presented using the √s = 7 TeV dataset only.
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Spearman, William R. "Measurement of the mass and natural width of the Higgs boson in the H to ZZ to 4l decay channel with the ATLAS detector." Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:13070058.
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This thesis presents a measurement of the mass, natural width, and signal strength, defined as the yield normalized to the Standard Model prediction, of the Higgs boson in the \(H \rightarrow ZZ^{(*)} \rightarrow 4l\) decay channel using an approach which utilizes event-by-event detector response information. The measurement is performed on p-p collision data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The data corresponds to an integrated luminosity of \(25 fb^{-1}\) with center-of-mass energies of 7 TeV and 8 TeV. The measured mass of the Higgs boson is \(m_H = 124.57_{-0.43}^{+0.48} GeV\). The signal strength was estimated at \(\mu = 1.76_{-0.37}^{+0.46}\). Finally, the natural width of the Higgs was determined to be < 2.6 GeV with 95% confidence. The event-by-event approach used in this analysis involves the parameterization of the behavior of single leptons in the ATLAS detector and the convolution of a mass response with the Higgs truth distribution to derive the reconstruction level signal model.Physics
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Flechl, Martin. "Looking for the Charged Higgs Boson : Simulation Studies for the ATLAS Experiment." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-110882.
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The discovery of a charged Higgs boson (H+) would be an unambiguous sign of physics beyond the Standard Model. This thesis describes preparations for the H+ search with the ATLAS experiment at the Large Hadron Collider at CERN. The H+ discovery potential is evaluated, and tools for H+ searches are developed and refined. The H+→τν decay mode has been known as the most promising H+ discovery channel. Within this thesis, first studies of this channel with realistic detector simulation, trigger simulation and consideration of all dominant systematic uncertainties have been performed. Although, as shown by these studies, the discovery sensitivity is significantly degraded compared to studies using a parametrized detector simulation, this channel remains the most powerful ATLAS H+ discovery mode. Future searches will rely on multivariate analysis techniques like the Iterative Discriminant Analysis (IDA) method. First studies indicate that a significant sensitivity increase can be achieved compared to studies based on sequential cuts. The largest uncertainty in H+ searches is the expected $t\bar{t}$ background contribution. It is shown that numbers obtained from simulated events could be off by a factor of two, decreasing the discovery sensitivity dramatically. In this thesis, the Embedding Method for data-driven background estimation is presented. By replacing the muon signature in $t\bar{t}$ events with a simulated τ, events which allow an estimation of the background contribution at the 10% level are obtained. The ATLAS τ identification focuses on comparably clean environments like Z and W decays. To optimize the performance in high-multiplicity events like H+→τν, tau leptons are studied in $t\bar{t}$ and pile-up events. Variables which do not show discrimination power in high-multiplicity events are identified, and in some cases similar, more powerful variables are found. This allows to recover some of the performance loss and to increase the robustness of the τ identification. For the analysis of large amounts of data produced by the ATLAS detector, seamless interoperability of the various Grid flavors is required. This thesis introduces translators to overcome differences in the information system between a number of Grid projects,and highlights important areas for future standardization.
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Pilot, Justin Robert. "Search for the Higgs Boson in the ZH → μ+μ−bb̄ Channel at CDF Using Novel Multivariate Techniques." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1321973499.
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Flowers, Sean Christopher. "Search for the Standard Model Higgs boson produced in association with top quarks in the lepton plus jets channel." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu150043192139632.
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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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Isacson, Max. "Studies of a neutral Higgs boson produced in gluon-gluon fusion and vector boson fusion." Thesis, Uppsala universitet, Högenergifysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-239238.
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This paper presents an outline of the generation of mass for the massive Standard Model particles (fermions, $W^\pm$, $Z^0$) through electroweak symmetry breaking via the Higgs mechanism, and how the Higgs boson emerges from this framework. A Monte Carlo study was done on the decay $H\rightarrow\tau\tau$, with one leptonically and one hadronically decaying tau, with two different production channels for the $H$, gluon-gluon fusion (gg) and vector boson fusion (VBF), at $\sqrt s = 7\tev$ with a Higgs mass $m_H = 120\gev$. The kinematics of these two production channels were compared and it was found that the transverse momentum of muons produced in VBF were higher on average than those produced in gg. This differance was greater in muons originating from the leptonically decaying tau in the Higgs decay, than those produced by other processes in the underlying event. In the latter, however, the difference was still noticable. Jets were slightly more abundant in VBF than in gg, and were in VBF more distributed along the beam axis. The separation in pseudorapidity between the two jets with highest transverse momentum was found to be greater in VBF than in gg. An attempt to reconstruct the Higgs mass using Monte Carlo data run through a simulation of the ATLAS detector was done. The estimator used was the transverse mass of the system consisting of the visible part of the hadronically decaying tau, the lepton from the leptonically decaying tau and the total missing transvese energy. In gg the mean of the transvese mass distribution was found to be $89.26\gev$ with a root mean square uncertainty (RMS) of $23.86\gev$. In VBF the mean was found to be $85.57\gev$ with RMS $27.08\gev$.
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Ralph, Duncan (Duncan Kelley). "Observation and examination of a Higgs boson in the ZZ to four lepton channel." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91388.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014.71
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 119-123).
Results are presented on 5.1 fb- 1 of proton-proton collisions at a center of mass energy of 7 TeV and 19.7 fb- 1 at 8 TeV in a search for decays of the Standard Model (SM) Higgs boson to two Z bosons to four charged leptons. We observe a single excess above background expectation with a significance of 7.4 standard deviations at a mass of 125.6 ±0.4(stat) ±0.2(syst) GeV. This excess has a signal strength parameter ... We examine the transverse momentum spectrum of the new particle and find it to be consistent with the SM expectation, and also determine that the Standard Model JPC = 0++ is favored over the plausible alternative hypotheses.
by Duncan Ralph.
Ph. D.
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Wilson, Jonathan S. "A Search for the Standard Model Higgs Boson Produced in Association with Top Quarks." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1324333673.
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Zimmer, Stephan. "Charged Higgs Boson Studies in ttbar -Dilepton Events at the LHC." Thesis, Uppsala University, High Energy Physics, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-119325.
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A generator-level study of dilepton ttbar events to search for light charged Higgs bosons at the LHC is presented with the aim of finding a new variable to discriminate between charged Higgs signals and Standard Model signatures. The spin effects in leptonic decays of H± and W bosons are studied and a new angular distribution is identified as a discriminating variable. Studies are performed for different charged Higgs masses at two different center ofmass energies. Monte Carlo samples of Z+jets production are also used to test the analysis.
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Boddy, Christopher. "A search for the Standard Model Higgs boson via its decay to tau leptons and W bosons at the ATLAS detector." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:abba39e7-4de1-46c5-a533-7b677ae254f2.
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Understanding the origin or Electroweak symmetry breaking within the Standard Model was a key motivation for the construction of the Large Hadron Collider (LHC) experiment at CERN. This thesis presents a search for evidence of Higgs boson production in the 4.7 fb−1 of collision data recorded at a centre-of-mass energy of 7 TeV at the ATLAS detector during 2011. This search is focused on signal events in which a Higgs boson is produced in the mass range 100 < mH < 180 GeV/c2 and subsequently decays to a pair of W bosons or a pair of tau leptons to final states with one hadronically decaying tau lepton and one light lepton. After an event selection criteria has been applied, the number of events in this data sample is consistent with the total background estimate and an upper limit is placed on the SM Higgs boson production rate at 95% confidence level. In addition, the prospects for measuring the SM Higgs coupling strength to tau leptons with the associated Higgs production channels and the full LHC dataset are also presented.
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Dilsiz, Kamuran. "Effects of Aging in the Hadronic Forward Calorimeter on the Vector Boson Fusion Higgs Search." Thesis, University of Iowa, 2013. https://ir.uiowa.edu/etd/4840.
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Vector Boson Fusion (VBF) Higgs production is one of the methods that is being used to search for the existence of the Standard Model (SM) Higgs boson, and the Hadronic Forward Calorimeter (HF) is one of the main calorimeters in the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC). In this thesis, we looked at the effects of aging in the HF on the VBF Higgs search by using Fast Simulation to model accumulated radiation dosage effects. After proton-proton collisions at the LHC, vector bosons are radiated from quarks and a Higgs boson is produced. In this study, the Higgs boson is forced to decay into tau pairs. The VBF process produces two jets at low angles. We looked for two forward jets, reconstructed in HF and passing analysis thresholds. Thus, we observed jet tagging efficiencies for different levels of radiation damage in HF. Then, we compared the effect of radiation damage for different regions of HF, dividing HF into four regions. Analysis results showed that the VBF signal is not significantly diminished by the effects of aging in the HF.
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Jeske, C. "Evidence for the Higgs boson Yukawa coupling to tau leptons with the ATLAS detector." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/77753/.
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Mercurio, Kevin. "A Search for the Higgs Boson Produced in Association With a Vector Boson Using the ATLAS Detector at the LHC." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:14226092.
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This dissertation presents two searches for the Standard Model Higgs boson produced in association with a vector boson and decaying via $H\to b\bar{b}$. Specifically, the processes are: \llbb\ alone, and again in combination with the \vvbb\ and \lvbb\ processes. The dataset used for the analysis consists of 4.7 fb$^{-1}$ at $\sqrt{s} = $7~TeV and 20.3 fb$^{-1}$at $\sqrt{s} = $8~TeV from LHC collisions. The search was optimized without bias to a particular mass of the Standard Model Higgs boson.
Background processes contributing to the total number of observed events are estimated using a combination of Monte Carlo simluation and data-driven techniques. Utilizing a maximum-likelihood analysis, an observed upper limit on the cross section at the 95\% confidence interval for the \llbb\ channel is set at 2.76 times the Standard Model cross section with an expected limit of 2.54, and the observed upper limit for the combined search is 2.3 times the Standard Model cross section, with an expected limit of 1.01. Furthermore, compatibility with the Standard Model expectation is evaluated through the parameter $\mu$ = $\frac{\sigma_{observed}}{\sigma_{Standard Model}}$ and found to be $0.17\pm1.4$ for the \llbb\ analysis, and $1.09\pm0.61$ for the combined analysis, both consistent with the Standard Model expectation of 1.
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Olivares, Sebastian Andres. "Measurement of the Higgs boson off-shell coupling to constrain the total width in the H → ZZ(*) → 4ℓ channel and Level-1 Track muon isolation performance for the HL-LHC with the ATLAS detector." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/25378.
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Since the observation of a narrow mass resonance consistent with the Higgs boson by ATLAS and CMS collaborations in 2012, a number of important studies have been made in order to understand the properties of the newly discovered particle. The most fundamental precision measurements include the Higgs coupling to other particles and itself; properties that have a direct relation with the total decay width. The theoretical total width of the Standard Model (SM) Higgs boson is extremely small (4.2 MeV), making its direct measurement by the LHC experiments non feasible due to the finite experimental detector resolution. Recent publications have shown a novel way to set an indirect limit on the total Higgs boson width by using measurements of both off-shell and on-shell production. This thesis presents a determination of the off-shell Higgs boson coupling, and a further interpretation of the Higgs total width in the H → ZZ → 4l channel (l = e; μ). The results are based on pp collision data collected by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 20.3 fb-1 at a collision energy of √s = 8 TeV. Using the CLs statistical method and assuming the same higher-order QCD corrections applied for both signal and background processes, the observed 95% confidence level (CL) upper limit on the off-shell signal strength is 7.3 (with the yields normalized to the SM expectation). Similarly, the 95% CL upper limit on the Higgs total width is 24.7 MeV. The LHC will undergo its last big upgrade in 2021, in preparation for the high-luminosity LHC Run (HL-LHC), with a luminosity increase of approximately a factor of 5 beyond its nominal design rate. Raising the muon transverse momentum threshold becomes a necessity in order to maintain a low online selection rate with the existing trigger system, at the cost of a reduced efficiency for the electroweak scale physics. An alternative to this approach is a proposed design of a first-level hardware trigger that uses tracking information. Being able to use tracking information at the first level of the ATLAS trigger in the implementation of a muon isolation algorithm offers an extra handle for differentiating between signal and background. The second part of this thesis presents studies on the performance of tracking-based muon isolation designed for a first-level hardware trigger system. These studies demonstrate the improved trigger performance of the muon isolation algorithm when compared to an increase of the transverse momentum threshold of the muon candidates.
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Madsen, Alexander. "Hunting the Charged Higgs Boson with Lepton Signatures in the ATLAS Experiment." Doctoral thesis, Uppsala universitet, Högenergifysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-248659.
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This thesis presents searches for a charged Higgs boson (H±) in proton-proton collisions with center-of-mass energies of 7 TeV and 8 TeV, using data collected by the ATLAS experiment at the Large Hadron Collider at CERN. Multiple search channels are used with the common characteristic of at least one charged lepton (electron or muon) that effectively reduces the multi-jet background and is used for efficient triggering. Charged Higgs bosons decaying to a tau lepton and a neutrino are searched for using final states with two charged leptons, or one charged lepton and a hadronically decaying tau. A significant background originates from quark- or gluon-initiated jets that may be misidentified as hadronic tau decays. Methods to estimate this background are presented, including a largely data-driven matrix method. Signal processes with a charged Higgs boson mass below or above that of the top quark are considered. With the dataset collected at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb-1, upper limits at 95% confidence level are placed on the branching fraction B(t→bH±)×B(H±→τν) in the range 1.1–0.3% for charged Higgs boson masses between 80 GeV and 160 GeV, and on the top-quark associated H± production cross section in the range 0.93 to 0.03 pb for charged Higgs boson masses between 180 GeV and 1 TeV.
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Alwall, Johan. "Quark Distributions and Charged Higgs Boson Production : Studies of Proton Structure and New Physics." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5901.
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Yang, Mingming Ph D. Massachusetts Institute of Technology. "Observation and measurement of a standard model Higgs Boson-like diphoton resonance with the CMS detector." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/103183.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 193-201).
This thesis concerns the observation of a new particle and the measurements of its properties, from the search of the Higgs boson through its decay into two photons at the CMS experiment at CERN's Large Hadron Collider (LHC), on the full LHC "Run I" data collected by the CMS detector during 2011 and 2012, consisting of proton-proton collision events at [square root of] s = 7 TeV with L = 5.1 fb-1 and at [square root of] s = 8 TeV with L = 19.7 fb-1, with the final calibration. In particular, an excess of events above the background expectation is observed, with a local significance of 5.7 standard deviations at a mass of 124.7 GeV, which constitutes the observation of a new particle through the two photon decay channel. A further measurement provides the precise mass of this new particle as 124.72+0.35 -0.36 GeV = 124.72+0.31 -0.32(stat)+0.16 -0.16(syst) GeV. Its total production cross section times two photon decay branching ratio relative to that of the Standard Model Higgs boson is determined as 1.12+0.26 -0.23 = 1.12+0.21 -0.21(stat)+0.15 -0.09(syst), compatible with the Higgs boson expectation. Further extractions of its properties relative to the Higgs boson, including the production cross section times decay branching ratios for separate Higgs production processes, couplings to bosons and to fermions, and effective couplings to the photon and to the gluon, are all compatible with the expectations for the Standard Model Higgs boson.
by Mingming Yang.
Ph. D.
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Mountricha, Eleni. "Recherche du boson de Higgs du Modèle Standard avec l'expérience ATLAS au LHC résultante à la observation d'une nouvelle particule compatible avec le boson de Higgs." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00759636.
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Le sujet de cette thèse est la recherche du boson de Higgs du Modèle Standard par sa désintégration en quatre leptons avec l'expérience ATLAS au CERN. La théorie qui prédit le boson du Higgs est présentée et les contraintes de la théorie et des recherches directes et indirectes sont citées. L'expérience ATLAS et ses composants sont décrits et le Système de Contrôle du Détecteur pourle fonctionnement et la surveillance des blocs d'alimentation des chambres à tubes de dérive est détaillé. La reconstruction et l'identification des électrons et des muons sont résumées. Des études de performance sur les taux de faux muons, sur l'effet d'empilement sur l'isolation des muons, et sur l'efficacité de l'isolation et du paramètre d'impact des muons sont présentées. L'analyse de la désintégration de Higgs en quatre leptons est détaillée en mettant l'accent sur l'estimation du bruit de fond, les méthodes employées et les régions de contrôle utilisées. Les résultats de la recherche avec les données de 2011 à √s = 7TeV sont présentées, qui ont conduit à l'indication de l'observation du boson de Higgs. L'optimisation réalisée pour la recherche d'un boson de Higgs de basse masse est décrite et l'effet sur les données de 2011 sont présentés. L'analyse est effectuée avec les données de 2011 à √s = 8TeV collectées jusqu'au juillet et les résultats sont présentés, incluant la combinaison avec les données de 2011. Ces derniers résultats ont conduit à l'observation d'une nouvelle particule compatible avec le boson de Higgs du Modèle Standard.
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Herren, Florian [Verfasser], and M. [Akademischer Betreuer] Steinhauser. "Precision Calculations for Higgs Boson Physics at the LHC - Four-Loop Corrections to Gluon-Fusion Processes and Higgs Boson Pair-Production at NNLO / Florian Herren ; Betreuer: M. Steinhauser." Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/1221186914/34.
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Proissl, Manuel Daniel. "Dijet invariant mass studies in the Higgs boson H→bb- resonance search in association with a W/Z boson using the ATLAS detector." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10516.
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The Standard Model of Particle Physics describes the fundamental building blocks of matter and phenomena up to the highest particle interaction energies. The theory demands the existence of a scalar particle: the Higgs boson. The Higgs boson was discovered by the ATLAS and CMS collaborations at CERN using bosonic final states and is measured to have a mass of around 125 GeV. This particle is predicted to decay predominantly into pairs of b-quarks at this mass, but suffers from overwhelming backgrounds from the multijet production expected from QCD interactions. Therefore, H→bb- production in association with a leptonically decaying W or Z boson is considered, with Z → vv-, W → lv and Z → ll, where ` denotes electrons and muons. This thesis presents a search for the Higgs boson decaying into bb- pairs in association with a W or Z boson using the ATLAS detector at the Large Hadron Collider (LHC) at CERN. The analysis uses the full dataset recorded during pp collisions at the LHC in Run-1, corresponding to 4.7 fb-1 at √s = 7 TeV and 20.3 fb-1 at √s = 8 TeV. A multivariate technique and a kinematic cut-based approach have been used to maximize the signal over background ratio, where a particular emphasis on the latter approach is made in this thesis. Final state radiation and reconstruction effects may decrease the bb- resonance resolution significantly, while comparably decreasing the probability of observing the decay over the background. The b quark pairs from the Higgs boson are reconstructed as topological clusters formed to jets in the ATLAS calorimeter. Thus, the reconstruction and calibration of these jets are crucial for the final Higgs mass resolution and paramount for the search and for future precision measurements of V H, H→bb- production. This thesis presents the development and evaluation of advanced techniques to improve the invariant dijet mass reconstruction of the H→bb- candidate. Sequential jet calibrations, semileptonic corrections and pT corrections to account for the interplay between jet resolution/scale and the underlying signal pT spectrum obtained from Monte Carlo simulations have been studied. A major focus has been made on the development and evaluation of an event-level kinematic likelihood fitting framework to exploit the full kinematic potential of V H topologies within the detector uncertainties of the reconstructed final state signatures in order to improve the measurement of the b-tagged jet kinematics. The jet energy calibrations of the H→bb- signal candidates yield an overall improvement of the dijet invariant mass resolution of up to ~30%, and of the expected statistical significance of ~12%. The analysis procedure is validated using the resonant V Z(bb-) production in the same final states as for the Higgs boson search, and is observed, compatible with the Standard Model expectation, with a significance of 4.9 standard deviations and a signal strength of μ^V Z = 0:74+0:17 -0:16. For a Higgs boson mass of 125.36 GeV, the observed (expected) deviation from the background-only hypothesis is found with a significance of 1.4 (2.6) standard deviations and a signal strength is determined to be μ^V H = 0:52±0:32(stat.)±0:24(syst.).
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Miconi, Florian. "Recherche du boson de Higgs standard léger dans le canal WH avec la statistique finale de l'expérience DØ au Tevatron." Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00759356.
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Le mécanisme de Higgs, introduit en 1964, propose une solution à un problème majeur du modèle standard de la physique des particules : l'origine de la masse. Ce mécanisme prédit l'existence d'un boson scalaire, de masse non prédite par la théorie et qui n'a encore jamais été observé expérimentalement (Juin 2012). Le Tevatron, un accélérateur hadronique basé à Fermi National Accelerator Laboratory près de Chicago, a permis la prise de données à l'aide des deux détecteurs CDF et DØ depuis 1983 jusqu'en septembre 2011. Accumulant une statistique de près de 10fb-1 à analyser. La production associée du Higgs et d'un boson vecteur est le canal principal de recherche pour un Higgs standard léger. A l'aide des données collectées par DØ, nous recherchons ce mode de production. La production du boson de Higgs étant très rare, nous avons développé des techniques sophistiquées de manière à améliorer la sensibilité au signal, telles que l'identification des jets de quarks beaux ou encore des méthodes basées sur des discriminants multivariés. Au final, une approche statistique nous permet de poser une limite supérieure sur le taux de production du Higgs observé (resp. attendu) rapporté aux prédictions du modèle standard. Les résultats obtenus dans le canal WH avec la statistique finale de l'expérience DØ au Tevatron sont de 3.15 (resp. 3.97) pour un boson de Higgs de 115 GeV/C2.
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Scott, Darren James. "Effective field theories for top quarks at the LHC and physics beyond the Higgs boson." Thesis, Durham University, 2017. http://etheses.dur.ac.uk/12439/.
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In this thesis we have considered applications of two different types of effective field theory. The first of these, Soft Collinear Effective Theory (SCET) has been applied to the calculation of top quark pair production at hadron colliders. Building on factorisation theorems developed using SCET we present results for resummed differential cross sections of the top pair invariant mass. The highest accuracy of resummation achieved and matched to fixed order is at NNLO+NNLL'. Resummed predictions are compared to fixed order ones and we find that while the (N)NLO results can be sensitive to the choice of factorisation scale, the resummed results exhibit more stable behaviour. We perform a number of additional analyses to further investigate the choice of scale on the invariant mass distribution. In addition, we also present results for the p_T distribution of the top quark. The second piece of work presented in this thesis concerns the use of the Standard Model Effective Field Theory (SMEFT). The SMEFT augments the Standard Model with higher dimensional operators which can be viewed as the low energy realisation of some as yet undiscovered physics at high scale. We use the dimension-6 SMEFT to calculate the QCD corrections to Higgs decay to bottom quarks at NLO. The main result of this section is the NLO partial decay rate for the Higgs including the dimension-6 Wilson coefficients. Finally we attempt to remove the presence of large mass logarithms through the conversion of the b-quark mass to the MS‾ scheme. We assess the reliability of this prediction in the limit of massless bottom quarks and find excellent agreement with the result with full mass dependence.
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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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Vásquez, Tocora Andrés Felipe. "Enhancement in the double Higgs boson production by e+ e− annihilation and physics beyond the standard model." São Paulo, 2018. http://hdl.handle.net/11449/157221.
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Orientador: Rogério RosenfeldCoorientador: Alberto Tonero
Banca: Ricardo D'Elia Matheus
Banca: Enrico Bertuzzo
Abstract: The main goal of this dissertation is to show the enhancement of the cross-section for the double Higgs production through pair annihilation by including effective interactions and through the non-perturbative Sommerfeld effect. Bounds to some Wilson coefficients were obtained from such enhancement, this in the scenarios of the future e+ e− -colliders (FCC-ee, ILC, CLIC). In order to achieve this, some computational tools were implemented: FeynRules, FeynArts, FormCalc, and LoopTools. It is also shown the enhancement of the double Higgs production in 2HDM and MSSM, discussing the general framework of these two models. In addition, it is studied the threshold behavior of the cross-section for the double Higgs production when a hidden sector couples to the Higgs boson, yielding resonances below the threshold energy due to non-perturbative effects. We study the Sommerfeld effect in the double Higgs production in the scenario of e+ e− -colliders. The enhancement is discussed as generated from a hidden sector coupled to the Higgs boson. Below and above threshold enhancements are presented. Such analysis is of importance in the ILC project, which will operate up to the threshold energy √s = 250 GeV. The results has been achieved by the use of computational tools like FeynArts, FormCalc, and LoopTools
Resumo: O objetivo principal dessa dissertação é, mostrar o aprimoramento da seção de choque para a produção em dobro dos bósons de Higgs, por meio de aniquilação de pares, incluindo interações efetivas e através do efeito não perturbativo de Sommerfeld. De tais aprimoramentos, os limites para alguns coeficientes de Wilson foram obtidos, isso nos cenários de futuros aceleradores de e+e- (FCC-ee, ILC, CLIC). Para atingir estes resultados, algumas ferramentas computacionais foram implementadas: FeynRules, FeynArts, FormCalc e LoopTools. Também, é mostrado o aprimoramento da produção em dobro de bósons de Higgs no "2HDM" e "MSSM", discutindo o marco geral desses dois modelos. Além disso, foi estudado o comportamento, perto do limite de produção, da seção de choque da produção em dobro dos bósons de Higgs, quando um setor escondido é acoplado ao Higgs, produzindo ressonâncias abaixo da energia limite de produção, devido à efeitos não perturbativos
Mestre
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Faivre, Hugo. "Potentiel effectif non-perturbatif : Limites sur la masse du boson de Higgs et applications dynamiques." Phd thesis, Université Louis Pasteur - Strasbourg I, 2006. http://tel.archives-ouvertes.fr/tel-00391727.
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Bianchini, Lorenzo. "Recherche du boson de Higgs du modèle standard dans la voie de désintégration en leptons taus avec l'expérience CMS au LHC." Phd thesis, Ecole Polytechnique X, 2012. http://pastel.archives-ouvertes.fr/pastel-00739907.
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Dans cette thèse, je présente mon travail effectué au sein de l'expérience CMS, et consacré à la recherche du boson de Higgs du modèle standard dans sa voie de désintégration en une paire de leptons tau. L'objectif original et la finalité de cette recherche est une contribution à la découverte du boson de Higgs au LHC. Après un résumé du cadre théorique et expérimental de ma thése, j'expose la technique particle-fow développée pour la reconstruction des événements hors ligne enregistrés par CMS. La reconstruction et l'identification des leptons tau dans CMS sont décrites en détail dans la thèse. Une attention particulière est consacrée à la discrimination entre les électrons et les leptons taus qui se désintégrant en voie semi-leptoniques (donnant des neutrinos et des hadrons). Un élément crucial dans l'étude H -> tautau est la reconstruction de la masse invariante. Sur ce sujet, j'ai apporté des contributions originales au développement d'un Dynamical Likelihood Model, appelé SVfit, pour estimer la masse totale de la paire des taus, et qui sera utilisé pour l'analyse. Enfin, une recherche du boson de Higgs SM dans la voie H -> tautau , base sur 4.9 1/fb de collisions pp à sqrt(s) = 7 TeV, est présentée. Des événements avec une paire de taus sont sélectionnés où l'un se désintégre de façon semi-leptonique (i.e. en hadrons et neutrinos) et l'autre en façon leptonique (i.e. en muons ou électrons et en neutrinos). Aucun excès par dessus aux bruits de fond prédicts par le SM n'a été observé. L'interprétation statistique des résultats à été faite dans le cadre du SM et elle est finalement traduite en limites au 95% CL sur la section efficace du signal.
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Eriksson, David. "Phenomenology of Charged Higgs Bosons and B-meson Decays." Doctoral thesis, Uppsala universitet, Kärn- och partikelfysik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9564.
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For more than 30 years the Standard Model has been the theoretical foundation for particle physics. The theory has been verified successfully by experimental tests. Its biggest shortcoming is the non-discovery of the Higgs boson,responsible for giving the other particles masses. Despite its success there are hints that the Standard Model is not the complete theory and many extensions of it, such as supersymmetry, have been proposed. Extended theories often predict the existence of a charged Higgs boson and its detection will be a clear sign of physics beyond the Standard Model. The main focus in this thesis is on various phenomenological aspects of the charged Higgs boson. For favorable mass and couplings direct detection is shown to be possible at the Large Hadron Collider in production with an associated W boson. It is also shown how a light charged Higgs can have measurable effects on spin correlations in decays of pair-produced top quarks. The charged Higgs boson can also be seen indirectly, in for example B-meson decays, which can be used to put constraints on its mass and fermion couplings. Exclusion limits in two supersymmetric models are given together with a comparison with the discovery potentials for the LHC experiments. A tool for calculating properties, such as masses and decays, of both charged and neutral Higgs bosons in the Two-Higgs-Doublet Model is also presented. B-meson decays can also be used to test aspects of the strong interaction. Part of this thesis deals with improving and applying phenomenological models to B-meson decays. Although these models are not derived from first principles, their success shows that they capture important features of non-perturbative strong interactions.