Dissertations / Theses on the topic 'Collider searches'
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Pratt, Tracey. "New physics searches in high mass dimuons at the collider detector at Fermilab." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269332.
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Fawcett, William James. "Supersymmetry searches at the LHC and their interpretations." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:562ef583-9686-4895-adb0-801d1abb291d.
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One of the primary goals of the CERN Large Hadron Collider is to search for new physics. Many such searches have been carried out, in particular searches for supersymmetry, yet no new physics beyond the Standard Model has been found. With a large number of free parameters introduced by frameworks such as supersymmetry, it can be difficult to interpret the null results of searches. The first analysis presented in this thesis attempts to tackle this difficulty head-on, and gives a summary of the constraints from the Run-1 ATLAS searches. A combination of 22 searches were used, with integrated luminosities of up to 20.3 inverse femtobarns of 7 and 8 TeV data. The results are interpreted in the context of the 19-dimensional phenomenological MSSM, and are presented in terms of the masses of supersymmetric particles. Constraints from dark matter, heavy flavour and precision electroweak measurements were incorporated, and results are also interpreted in terms of these observables. Properties of models missed by the Run-1 searches are also shown. The second analysis presented in this thesis documents a direct search for new physics, using 18.2 inverse femtobarns of 13 TeV data collected during 2015 and 2016 by the ATLAS detector. The search targets final states with large jet multiplicity (at least 7 to at least 10 jets), which can arise from the pair production of gluinos decaying via a cascade. Further requirements are imposed on the sum of masses of reclustered large-radius jets. No evidence for new physics is found, and the results are interpreted in both a model-independent way and in terms of two simplified supersymmetric models, one of which was inspired by the results of the first study. Limits on the gluino mass of up to 1600 GeV are set at the 95 % confidence level, extending previous limits.
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Lane, Jenna Louise. "Prospects for charged Higgs Boson searches at the Large Hadron Collider with early ATLAS data." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/prospects-for-charged-higgs-boson-searches-at-the-large-hadron-collider-with-early-atlas-data(517a7a6c-02a0-4ccb-ab2f-2e483de3c972).html.
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Owen, Simon. "Multijet background estimation for supersymmetry searches using the ATLAS detector at the Large Hadron Collider." Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/2854/.
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This thesis describes a data-driven technique for estimating the multijet background to Supersymmetry (SUSY) searches with no leptons using the ATLAS detector at the Large Hadron Collider. The technique is used to estimate multijet distributions in SUSY signal and control regions with 1 fb−1 of sqrt(s) = 7 TeV data collected by ATLAS in 2011. The systematic uncertainty on the estimates is reduced with the development and use of novel event shape triggers. Multijet estimates provided from the technique developed in this thesis are used by the ATLAS collaboration in several different SUSY searches.
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Miao, Xinyu. "Direct and Indirect Searches for New Physics at the Electroweak Scale." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/217061.
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The Standard Model (SM) of particle physics is widely taken as an elegant effective theory of nature at the electroweak scale, with new physics expected at higher energy. Collider searches and other experimental inputs play a vital role in our hunt for the unknown physics, offering great insights along the way and eventually establishing the extension to the SM. Here we present our studies on prospects of direct and indirect searches for three types of models beyond the SM. The Inert Doublet Model (IDM) extends the SM electroweak sector by an extra Higgs doublet with a Z₂-symmetry. We first examine the IDM dilepton signal at the LHC with a center-of-mass energy of 14 TeV and find it exceeding SM backgrounds at 3σ–12σ significance level, with 100 fb⁻¹ integrated luminosity. We further show that it is possible to obtain the IDM trilepton signal at the 5σ significance level, with an integrated luminosity of 300 fb⁻¹. The Left-Right Twin Higgs (LRTH) model solves the little Hierarchy problem by taking the SM Higgs as a pseudo-Goldstone boson from the spontaneous breaking of a global symmetry. We focus on the discovery potential of the heavy top quark partner in the LRTH model at the LHC. With a luminosity of 30 fb⁻¹ at the early stage of the LHC operation, we conclude that the heavy top partner could be observed at a significance level above 5σ. Supersymmetric extensions of the SM enable cancellations among loop corrections to the Higgs mass from bosonic and fermionic degrees of freedom, leading to a solution to the well-known Hierarchy problem. However, the supersymmetry has to be broken by certain mechanism. We present an exploration of the B-physics observables and electroweak precision data in three distinct soft supersymmetry-breaking scenarios. Projection for future sensitivities of the precision data is also explored.
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Dafinca, Alexandru. "Searches for supersymmetric partners of the bottom and top quarks with the ATLAS detector." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:7b5457ac-0521-4c8d-af03-d0a347ef3b60.
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Supersymmetry is a promising candidate theory that could solve the hierarchy problem and explain the dark matter density in the Universe. The ATLAS experiment at the Large Hadron Collider is sensitive to a variety of such supersymmetric models. This thesis reports on a search for pair production of the supersymmetric scalar partners of bottom and top quarks in 20.1 fb−1 of pp collisions at a centre-of-mass energy of 8 TeV using the ATLAS experiment. The study focuses on final states with large missing transverse momentum, no electrons or muons and two jets identified as originating from a b-quark. This final state can be produced in a R-parity conserving minimal supersymmetric scenario, assuming that the scalar bottom decays exclusively to a bottom quark and a neutralino and the scalar top decays to a bottom quark and a chargino, with a small mass difference with the neutralino. As no signal is observed above the Standard Model expectation, competitive exclusion limits are set on scalar bottom and top production, surpassing previously existing limits. Sbottom masses up to 640 GeV are excluded at 95% CLs for neutralino masses of up to 150 GeV. Differences in mass between ~b1 and ~X01 larger than 50 GeV are excluded up to sbottom masses of 300 GeV. In the case of stop pair production and decay ~t1 → b + ~X±1 and ~X±1 → ~X01 + W* with mass differences ▵m = m~X±1 − m~X01 = 5 GeV (20 GeV), stop masses up to 580 GeV (440 GeV) are excluded for m~X01 = 100 GeV. Neutralino masses up to 280 GeV (230 GeV) are excluded for m~t1 = 420 GeV for ▵m = 5 GeV (20 GeV). In an extension of this analysis, sbottom quarks cascade-decaying to at least a Higgs boson are searched for in final states with large missing transverse momentum, at least 3 b-tagged jets and no electrons or muons, using neural network discriminants.
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Grout, Zara. "Supersymmetry searches in events with at least four leptons using the ATLAS detector at the Large Hadron Collider." Thesis, University of Sussex, 2015. http://sro.sussex.ac.uk/id/eprint/57321/.
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This thesis presents a search for supersymmetry using the dataset taken by ATLAS at the Large Hadron Collider with ps =8 TeV during 2012. Events with four or more leptons are selected and required to satisfy additional kinematic criteria that define optimised signal regions. These criteria are chosen to reject the majority of events produced by Standard Model processes, whilst retaining a large fraction of events produced by a variety of proposed supersymmetry scenarios. The expected number of Standard Model events are estimated using a combination of Monte Carlo and data-driven methods, the predictions of which are tested against data in specifically designed validation regions. No significant deviations from the Standard Model estimations are observed within statistical and systematic uncertainties. Exclusion limits are then set at 95% confidence level (CL) on a wide range of R-parity conserving and R-parity violating supersymmetry simplified models, as well as models of general gauge mediated supersymmetry. In R-parity violating models, 95% CL exclusion limits of 1350 GeV and 750 GeV are set on the masses of gluinos and charginos respectively. Exclusion limits are also set at 95% CL up to 620 GeV on the mass of heavy neutralinos for an R parity conserving scenario with decays via righthanded sleptons. Results are also presented for the combination of the four lepton analysis with another lepton-rich supersymmetry search.
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Sparrow, Alexander. "Measurement of the polarisation of the W boson and application to supersymmetry searches at the Large Hadron Collider." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/10212.
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This thesis gives an account of two analyses performed using data from the Compact Muon Solenoid experiment at the Large Hadron Collider. The first analysis measures the polarisation of W bosons with large transverse momentum using 36 pb⁻¹ of data collected in 2010. The second applies similar techniques to a search for supersymmetry in events containing a single lepton, jets and missing transverse energy. This analysis utilises 1.14 fb⁻¹ of data collected up to 2011. Background material related to the Standard Model, supersymmetry and the experimental apparatus are reviewed in detail. The W polarisation measurement is performed in both the W->ev and W->μv channels. The expected effect, a large dominance of the left-handed over the right-handed helicity state, is observed with a significance of 7.8σ for the W⁺ and 5.1σ for the W⁻ in the muon channel. Similar results are found in the electron channel and for a combined fit to both lepton channels. The second analysis conducts a search for supersymmetry in events containing a single lepton, jets and missing transverse energy. The search employs techniques developed for the W polarisation measurement to separate supersymmetry from Standard Model backgrounds. No deviation from the Standard Model is observed. A detailed statistical interpretation is performed and used to set limits within the Constrained Minimal Supersymmetric Standard Model as well as two simplified models.
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Buckingham, Ryan Mark. "Searches for new physics using Dijet Angular Distributions in proton-proton collisions at √s = 7 TeV collected with the ATLAS detector." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:25b20fa4-8e79-43b9-83de-225f17e333ea.
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Angular distributions of jet pairs (dijets) produced in proton-proton collisions at a centre-of- mass energy √s = 7 TeV have been studied with the ATLAS detector at the Large Hadron Collider using the full 2011 data set with an integrated luminosity of 4.8 fb−1, and reaching dijet masses up to 4.5 TeV. All angular distributions are consistent with QCD predictions. Analysis of the dijet angular distribution, using a novel technique simultaneously employing the dijet mass, is employed. This analysis is sensitive to both resonant new physics and phenomena with a slow-onset in mass. Using this technique, new exclusion limits have been set at 95% credibility level for several hypotheses of physics beyond the standard model including: quantum gravity scales, with 6 extra dimensions, below 4.11 TeV, quark contact interactions below a compositeness scale of 7.6 TeV, and excited quarks with a mass below 2.75 TeV. In a large and complex scientific experiment, such as ATLAS, the collection, management and usability of coherent data and metadata is a challenging operation. The availability of these data to physicists within the experiment is essential to all analysis efforts. A new web-based interface called “RunBrowser”, which makes ATLAS and LHC operations data available to the ATLAS Collaboration, is introduced.
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Vogl, Stefan [Verfasser], Alejandro [Akademischer Betreuer] Ibarra, and Björn [Akademischer Betreuer] Garbrecht. "Majorana Dark Matter: The Power of Direct, Indirect and Collider Searches / Stefan Vogl. Gutachter: Alejandro Ibarra ; Björn Garbrecht. Betreuer: Alejandro Ibarra." München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1053762119/34.
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Chaus, Andrii. "Searches for Dark Matter particules and development of a pixellized readout of the Time Projection Chamber for the International Linear Collider (ILC)." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112300.
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Le collisionneur linéaire international (ILC) est prévu pour être le prochain grand projet de la physique des hautes énergies. ILC est proposé avec deux détecteurs, International Large Detector (ILD), et Silicon Detector (SID). Cette thèse s’est déroulée dans le cadre de l'ILD. L'un des principaux composants du détecteur ILD est la chambre à projection temporelle (TPC). Cette thèse se concentre sur le développement de la lecture de la TPC, basée sur l'intégration des détecteurs de gaz Micro-pattern (Micromegas) et de puces CMOS pixels ("Timepix"). Ce nouveau type de dispositif est appelé "Ingrid". Les exigences principales pour "Ingrid" sont d’atteindre la sensibilité aux électrons uniques et d’obtenir une très haute résolution spatiale (~ 30 µm). Avec une TPC, on reconstruit les traces en utilisant le profil 2D des charges sur la plaque a l’extrémité de la TPC et la troisième coordonnée est dérivée du temps de dérive. Dans le cadre de cette thèse, une mini-TPC a été construite a Saclay dans le but de tester plusieurs prototypes de détecteurs "Ingrid". En outre, un système compose de 8 puces nommé "Octopuce" a été construit pour développer des algorithmes de reconstruction de traces. Nous avons effectué plusieurs mesures à l'aide de source radioactive à Saclay. Par ailleurs, de grands modules ont été testés avec un prototype de grande TPC (LP) sur un faisceau de test à DESY. Les résultats obtenus avec deux modules différents ont été présentés et les résultats sont en bon accord avec la prédiction théorique. La présence de la matière noire fournit une bonne indication d'apparition de nouveaux phénomènes a proximité de l'échelle électrofaible, et l'hypothèse populaire d’existence des WIMP doit être testé. Comme les couplages des WIMP aux différentes espèces de particules du modèle standard sont a priori inconnus, la recherche de la production de WIMP en collisions e+e- est complémentaire à la production dans les collisions pp ou a la détection directe de WIMPs primordiaux par leur diffusion sur des nucléons. Dans ce travail, nous étudions possibilité de découverte (ou l'exclusion) de production de paires de WIMPs avec l’ILC. Dans ce processus, un unique photon est rayonne dans l'état initial et une énergie manquante est requise. Nous montrons que l’ILC peut découvrir cette signature, même si l'annihilation en paires électron-positon contribue faiblement au taux d’annihilation de la matière noire dans l'univers primordial. Nous avons traduit la sensibilité en terme d’échelles de masse pour différents types d’opérateurs effectifs et montré que la masse et les couplages des WIMPs peuvent être mesurés avec une précision de l’ordre de 1% si leur détection est avérée. En outre, des études de production de WIMPs avec l’ILC sont complémentaires aux études avec des états finaux mono-X au LHC, car ils testent le couplage WIMP-lepton. Au LHC, le couplage WIMP-proton est testé a une l'échelle de 1 TeV. Avec l’ILC, en utilisant une luminosité intégrée de 500 fb⁻¹, une énergie dans le centre de masse de √s = 500 GeV et avec des faisceau non polarisés, une limite pour l’échelle sur l'interaction de contact Λ de l’ordre de 2 TeV est accessible. De plus, les configurations de polarisation appropriées permettent d'améliorer la sensibilité pour les recherches de matière noire à l’ILC, en supposant que le couplage des paires de WIMP aux électrons et aux positons dépend du choix de l'opérateurThe International Linear Collider (ILC) is planned to be the next major project in the High Energy Physics. ILC is proposed to have two detectors, namely International Large Detector (ILD), and Silicon Detector (SiD). This thesis is done in the framework of the ILD. One of the main components of the ILD detector is the Time Projection Chamber (TPC). This PhD thesis concentrates on the development of TPC readout, based on integration of the Micro-pattern gas detectors (Micromegas) and CMOS pixel chips ("Timepix"). This new type of device is named "InGrid". Main requirements for "InGrid" is to achieve sensitivity to single electrons and a very high spatial resolution (~30 μm). In TPC one reconstructs tracks using 2D-charge profile on the TPC endplate and the third coordinate is derived from the drift time information. In Saclay mini-TPC was built. Using this mini-TPC, several prototype "Ingrid" detectors have been tested in the course of this PhD. In addition, 8-chips system named “Octopuce” was built to develop track reconstruction algorithms. We have performed several measurements using laboratory radioactive source in Saclay. In addition, the large modules were tested at a Large TPC Prototype (LP) in a test beam area at DESY. Results with two different modules were presented. Obtained results well agreed with theoretical prediction. The existence of Dark Matter provides a strong indication for the appearance of new phenomena near the electroweak scale, and the popular WIMP hypothesis is out there to be tested. Since the couplings of WIMPs to different species of Standard Model particles are a priori unknown, the investigation of WIMP production in e+e- collisions is fundamentally complementary to production in pp collisions or direct detection of primordial WIMPs scattering on nucleons. In this work we investigate the discovery (or exclusion) reach of the ILC based on the production of a pair of WIMPs, which recoils against an energetic photon from initial state radiation. We show that the ILC can discover this signature even if annihilation to electrons provides only a small fraction of the total dark matter annihilation rate in the early universe. We translated the sensitivity into mass scales of various effective operators and showed that the WIMPs mass and couplings can be measured at the percent level in case of an observation. Furthermore, WIMPs studies on ILC are complementary to current LHC in the mono-X final states, because they test WIMP-lepton coupling. LHC studies WIMP-proton coupling at the scale of 1 TeV. ILC could reach limits up to 2 TeV on the contact interaction scale Λ for the vector operator by using an integrated luminosity at 500 fb⁻¹, at the center-of-mass √s = 500 GeV with unpolarized beams. Moreover, proper polarization configurations allows to improve sensitivity for the Dark Matter searches at the ILC, assuming WIMPs pair couple differently to electron and positron for different operators
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Beresford, Lydia Audrey. "Searches for dijet resonances using √s = 13 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:c516b04b-2763-487a-a633-6c506cec93ad.
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This thesis presents three searches for new resonances in dijet invariant mass spectra. The spectra are produced using √s = 13 TeV proton-proton collision data recorded by the ATLAS detector. New dijet resonances are searched for in the mass range 200 GeV to 6.9 TeV in mass. Heavy new resonances, with masses above 1.1 TeV, are targeted by a high mass dijet search. Light new resonances, with masses down to 200 GeV, are searched for in dijet events with an associated high momentum object (a photon or a jet) arising from initial state radiation. The associated object is used to efficiently trigger the recording of low mass dijet events. All of the analyses presented in this thesis search for an excess of events, localised in mass, above a data-derived estimate of the smoothly falling QCD background. In each search no evidence for new resonances is observed, and the data are used to set 95% C.L. limits on the production cross-section times acceptance times branching ratio for model-independent Gaussian resonance shapes, as well as benchmark signals. One particular benchmark signal which is considered in all of the searches is an axial-vector Z' dark matter mediator model whose parameter space is reduced due to the results presented in this thesis.
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Dimitriadi, Christina. "Unfolding of multivariate tools and statistical analysis for Higgs boson pair production searches in the ATLAS detector at the Large Hadron Collider." Thesis, Uppsala universitet, Högenergifysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-394393.
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Recently, searches for pair production of Higgs bosons in several final states have been carried out by the ATLAS exeperiment at the Large Hadron Collider (LHC). This study focuses on the search for non-resonant di-Higgs production decaying to a final state with two b-jets and two τ-leptons using 36.1 fb-1 of data recorded by the ATLAS detector. The analysis for this process has already been performed. Boosted decision trees (BDTs) are used in the analysis to improve the separation of the signal from background processes and several variables that provide good discrimination between signal and background are used as inputs to the BDT. This study aims to unfold the BDT of the analysis and optimize a cut-based analysis so that the gain from using the BDT can be estimated. Two variables, related to the invariant masses and angular distances of the Higgs boson decay products, are defined and the optimal cuts are found to be Xmττmbb<1.8 and XΔRττΔRbb <4.0. Then, the upper limits on the SM HH production cross section are set when fitting mHH with the cut-based analysis. An expected limit of 0.78 pb, 23 times the SM prediction is obtained when neglecting systematic uncertainties, compared to the limit of 15 times the SM as recomputed when using the BDT. Comparing the two results, the sensitivity is worsened by 50% when not using the BDT.
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Jimenez, Fabricio. "Model independent searches for New Physics using Machine Learning at the ATLAS experiment." Thesis, Université Clermont Auvergne (2017-2020), 2019. http://www.theses.fr/2019CLFAC030/document.
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Nous abordons le problème de la recherche indépendante du modèle pour la Nouvelle Physique (NP), au Grand Collisionneur de Hadrons (LHC) en utilisant le détecteur ATLAS. Une attention particulière est accordée au développement et à la mise à l'essai de nouvelles techniques d'apprentissage automatique à cette fin. Le présent ouvrage présente trois résultats principaux. Tout d'abord, nous avons mis en place un système de surveillance automatique des signatures génériques au sein de TADA, un outil logiciel d'ATLAS. Nous avons exploré plus de 30 signatures au cours de la période de collecte des données de 2017 et aucune anomalie particulière n'a été observée par rapport aux simulations des processus du modèle standard. Deuxièmement, nous proposons une méthode collective de détection des anomalies pour les recherches de NP indépendantes du modèle au LHC. Nous proposons l'approche paramétrique qui utilise un algorithme d'apprentissage semi-supervisé. Cette approche utilise une probabilité pénalisée et est capable d'effectuer simultanément une sélection appropriée des variables et de détecter un comportement anormal collectif possible dans les données par rapport à un échantillon de fond donné. Troisièmement, nous présentons des études préliminaires sur la modélisation du bruit de fond et la détection de signaux génériques dans des spectres de masse invariants à l'aide de processus gaussiens (GPs) sans information préalable moyenne. Deux méthodes ont été testées dans deux ensembles de données : une procédure en deux étapes dans un ensemble de données tiré des simulations du modèle standard utilisé pour ATLAS General Search, dans le canal contenant deux jets à l'état final, et une procédure en trois étapes dans un ensemble de données simulées pour le signal (Z′) et le fond (modèle standard) dans la recherche de résonances dans le cas du spectre de masse invariant de paire supérieure. Notre étude est une première étape vers une méthode qui utilise les GPs comme outil de modélisation qui peut être appliqué à plusieurs signatures dans une configuration plus indépendante du modèleWe address the problem of model-independent searches for New Physics (NP), at the Large Hadron Collider (LHC) using the ATLAS detector. Particular attention is paid to the development and testing of novel Machine Learning techniques for that purpose. The present work presents three main results. Firstly, we put in place a system for automatic generic signature monitoring within TADA, a software tool from ATLAS. We explored over 30 signatures in the data taking period of 2017 and no particular discrepancy was observed with respect to the Standard Model processes simulations. Secondly, we propose a collective anomaly detection method for model-independent searches for NP at the LHC. We propose the parametric approach that uses a semi-supervised learning algorithm. This approach uses penalized likelihood and is able to simultaneously perform appropriate variable selection and detect possible collective anomalous behavior in data with respect to a given background sample. Thirdly, we present preliminary studies on modeling background and detecting generic signals in invariant mass spectra using Gaussian processes (GPs) with no mean prior information. Two methods were tested in two datasets: a two-step procedure in a dataset taken from Standard Model simulations used for ATLAS General Search, in the channel containing two jets in the final state, and a three-step procedure from a simulated dataset for signal (Z′) and background (Standard Model) in the search for resonances in the top pair invariant mass spectrum case. Our study is a first step towards a method that takes advantage of GPs as a modeling tool that can be applied to several signatures in a more model independent setup
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McFayden, Joshua A. "Searches for supersymmetric partners of third generation quarks and measurement of the tt ̄+Z process using the ATLAS detector at the CERN Large Hadron Collider." Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/5264/.
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This thesis presents results using data collected by the ATLAS experiment during 2011 and 2012 at √s = 7 TeV and 8 TeV respectively. The focus of the work presented in this thesis is separated into two areas, measurement of the tt ̄+Z process and searches for the supersymmetric partners to third generation quarks. Firstly, a search for tt ̄+ Z production using 4.7 fb−1 of √s = 7 TeV data is described including the generation of the dedicated simulated signal Monte Carlo samples for the analysis. The result is interpreted in terms of a 95% probability upper limit on the tt ̄+ Z production cross section of 0.71 pb. This is compatible with NLO Standard Model prediction of 0.14 pb. Secondly, a number of searches for the supersymmetric partners of bottom (sbottom) and top (stop) quarks are described. The first is a search for sbottom squark pair production in the b_1 → b_1 χ^0_1 decay channel using 2.05 fb−1 of √s = 7 TeV ATLAS data. No significant excess is observed above the Standard Model expectation and exclusion limits at the 95% confidence level are set in the m_b_1 − m_χ^0_1 plane. For a massless neutralino sbottom masses are excluded up to 390 GeV. For neutralino mass of 120 GeV sbottom masses are excluded for 275 < m_b_1 < 350 GeV. Finally two searches for stop squark pair production in the t_1 → t_! χ^0_1 decay channel are described, one using 4.7 fb−1 of √s = 7 TeV data and the other using 20.5 fb−1 of √s = 8 TeV data. Again, no significant excess is observed above the Standard Model expectation and exclusion limits at the 95% confidence level are set in the m_t1 − m_χ^0_1 plane. For a nearly massless neutralino, stop masses between 320 and 660 GeV are excluded. For neutralino mass of 150 GeV, stop masses are excluded between 400 and 620 GeV.
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Störig, Kathrin [Verfasser], and Gregor [Akademischer Betreuer] Herten. "QCD background estimation for Supersymmetry searches with jets and missing transverse momentum with the ATLAS experiment at the Large Hadron Collider = QCD Untergrundbestimmung für Suchen nach Supersymmetrie in einem Kanal mit Jets und fehlender transversaler Energie mit dem ATLAS Experiment am Large Hadron Collider." Freiburg : Universität, 2012. http://d-nb.info/1123473129/34.
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Wendland, Dennis Patrick. "Search for fourth generation b' quarks in same-sign dilepton final states with ATLAS." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16835.
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In dieser Dissertation wird eine Suche nach der Produktion von ''down''-artigen b'' Anti-b'' Quark-Antiquark-Paaren einer sequentiellen vierten Generation von Fermionen präsentiert. Für die Suche wurden Endzustände mit zwei gleich geladenen Leptonen (e oder mu), mindestens zwei Jets (davon ein b-Jet), fehlender transversaler Energie und einer großen Summe der Transversalimpulse aller Elektronen, Muonen und Jets betrachtet. Für den Zerfall dieser b'' Anti-b'' Quark-Antiquark-Paare wurden zwei verschiedene Szenarien untersucht. Im ersten Szenario wird angenommen, dass beide b'' Quarks ausschliesslich in ein t Quark und ein W Boson zerfallen. Für das zweite Szenario werden variable Verzweigungsverhältnisse für die Zerfälle der b'' Quarks nach tW, cW und uW erlaubt. Die Suche wurde mit Daten durchgeführt, die von pp Kollisionen mit einer Schwerpunktsenergie von sqrt(s) = 8 TeV vom ATLAS Detektor am Large Hadron Collider aufgezeichnet wurden. Der benutzte Datensatz entspricht einer integrierten Luminosität von 14.3 fb^-1. Es wurde kein signifikanter Überschuss an Ereignissen über den erwarteten Ereignissen vom Untergrund beobachtet. Daher wurde im ersten Szenario eine untere Grenze auf die b''-Masse (m_b'') von 0.724 TeV mit einem Konfidenzniveau von 95% bestimmt. Im Falle des zweiten Szenarios mit variablen Verzweigungsverhältnissen wurden Ausschlussregionen mit einem Konfidenzniveau von 95% als Funktion der Masse des b''-Quarks und seiner Verzweigungsverhältnisse bestimmt. Die erhaltenen Grenzen auf m_b'' sind schwächer verglichen mit dem Ergebnis für ein Verzweigungsverhältniss von 100% für b''->tW.This thesis presents a search for the production of down-type b'' anti-b'' quark-antiquark pairs of a sequential fourth generation of fermions. In this search, final states with two same-sign charged leptons (e or mu), at least two jets (including at least one b-jet), missing transverse energy and a large total sum of the transverse momenta of all electrons, muons and jets were considered. Two different scenarios were assumed for the decays of these $b'' anti-b'' quark pairs. In the first scenario the two b'' quarks were considered to decay exclusively into a t quark and a W boson. For the second scenario, variable branching fractions for the decays of the b'' quarks into tW, cW and uW were allowed. The search was performed using data from pp collisions at a center-of-mass energy of sqrt(s) = 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. The used dataset corresponds to an integrated luminosity of 14.3 fb^-1. No significant excess of events over the background expectation was observed. Hence a lower limit on the b'' mass of 0.724 TeV was set with 95% confidence level in the first scenario. In case of the second scenario with variable branching fractions, exclusion areas with 95% confidence level were derived as a function of the b'' mass and its decay branching fractions. These limits are less stringent compared to the result assuming a branching fraction of 100% for b''->tW.
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Love, Jeremy R. "A search for technicolor at the Large Hadron Collider." Thesis, Boston University, 2012. https://hdl.handle.net/2144/31586.
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Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
The Standard Model of particle physics provides an accurate description of all experimental data to date. The only unobserved piece of the Standard Model is the Higgs boson, a consequence of the spontaneous breaking of electroweak symmetry by the Higgs mechanism. An alternative to the Higgs mechanism is proposed by Technicolor theories which break electroweak symmetry dynamically through a new force. Technicolor predicts many new particles, called Technihadrons, that could be observed by experiments at hadron colliders. This thesis presents a search for two of the lightest Technihadrons, the ρT and ωT . The Low-Scale Technicolor model predicts the phenomenology of these new states. The ρT and ωT are produced through qq annihilation and couple to Standard Model fermions through the Drell-Yan process, which can result in the dimuon final state. The ρT and ω T preferentially decay to the πT and a Standard Model gauge boson if kinematically allowed. Changing the mass of the πT relative to that of the ρT and ωT affects the cross section times branching fraction to dimuons. The ρT and ωT are expected to have masses below about 1 TeV. The Large Hadron Collider (LHC) at CERN outside of Geneva, Switzerland, produces proton-proton collisions with a center of mass energy of 7 TeV. A general purpose high energy physics detector ATLAS has been used in this analysis to search for Technihadrons decaying to two muons. We use the ATLAS detector to reconstruct the tracks of muons with high transverse momentum coming from these proton-proton collisions. The dimuon invariant mass spectrum is analyzed above 130 GeV to test the consistency of the observed data with the Standard Model prediction. We observe excellent agreement between our data and the background only hypothesis, and proceed to set limits on the cross section times branching ratio of the ρT and ωT as a function of their mass using the Low-Scale Technicolor model. We combine the dielectron and dimuon channels to exclude masses of the ρT and ωT between 130 GeV - 480 GeV at 95% Confidence Level for masses of the πT between 50 GeV - 480 GeV. In addition for the parameter choice of m(π T ) = m(ρT /ω T )- 100 GeV, 95% Confidence Level limits are set excluding masses of the ρT and ωT below 470 GeV. This analysis represents the current world's best limit on this model.
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Wells, Phillippa Scott. "Search for the top quark at the CERN pp collider." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335204.
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Wildish, Anthony James. "Search for double parton scattering at the CERN proton-antiproton collider." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47708.
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Coadou, Yann. "Searches for the Charged Higgs at Hadron Colliders Based on the Tau Lepton Signature." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3564.
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Jarvis, Chad. "A search for Z boson pair production at the fermilab tevatron collider." College Park, Md.: University of Maryland, 2007. http://hdl.handle.net/1903/7624.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Dept. of Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Moeller, Victoria. "A search for strong gravity effects with the ATLAS experiment." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608295.
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Krop, Dan. "A search for neutral B meson oscillations at the Tevatron collider experiment DO." [Bloomington, Ind.] : Indiana University, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3264318.
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Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2007.Source: Dissertation Abstracts International, Volume: 68-05, Section: B, page: 3121. Adviser: Rick Van Kooten. "Title from dissertation home page (viewed Jan. 24, 2008)."
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Scoville, James. "Searching for new particles at the Large Hadron Collider : theory and methods for extradimensional supersymmetry." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:82d58c67-bb2a-4f03-b186-9e6524b5b255.
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The hierarchy problem of the electroweak scale is an intriguing puzzle which can conceivably be solved during upcoming runs of the Large Hadron Collider (LHC). Supersymmetry (SUSY) is an attractive potential solution to this problem, though the fact that no supersymmetric particles have been discovered thus far raises fine tuning of most models to ℴ(1%). Extradimensional SUSY is especially interesting in light of this fact since certain models are easier to reconcile with LHC data. This thesis discusses two different extradimensional SUSY scenarios: auto-concealment and Maximally Natural SUSY (MNSUSY). The auto-concealment mechanism applies when the lightest ordinary superymmetric particle (LOSP), a brane localized state, promptly decays to the Kaluza-Klein (KK) tower of a bulk lightest supersymmetric particle (LSP). This dynamically realizes the compression mechanism for hiding SUSY as decays into the more numerous heavier KK LSP states are favored. LHC limits on LOSP squarks weaken to ≲ 450 GeV while limits on LOSP right-handed sleptons evaporate. Slepton searches perform poorly in this case because LHC analyses are blind to compressed slepton spectra. To help fill this gap, this thesis presents a monojet-like search sensitive to the very compressed range 3 GeV < m ĩ â m∼x01 < 24 GeV. The analysis should allow LHC14 with 100 fbâ1 to search for degenerate left-handed selectrons and smuons in the compressed region up to m ĩL ≲ 150 GeV. In addition, it should be sensitive to m ĩL ≲ 110 GeV for auto-concealed SUSY. To expand the class of extradimensional SUSY models the LHC is able to test this thesis also describes the Lagrangian and mass matrices of MNSUSY, which are needed to implement this model in the Feynman rules generator program FeynRules for use in Monte Carlo programs for collider simulations. It also describes benchmark scenarios useful for the first collider phenomenology studies.
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Braithwaite, Jason John. "Visual search in space and time : where attention and inattention collide?" Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269885.
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Akatsuka, Shunichi. "Search for chargino and neutralino production using final states with two soft leptons in pp collisions at √s = 13 TeV." Kyoto University, 2020. http://hdl.handle.net/2433/253471.
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Chapleau, Bertrand. "Search for top-antitop quark resonances with the ATLAS detector at the Large Hadron Collider." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123013.
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The intriguing nature of the top quark, by far the heaviest particle in the Standard Model of particle physics, has motivated the development of many theoretical extensions predicting the existence of new massive particles decaying to a pair of top-antitop quarks. The production of these hypothetical particles in proton-proton collisions at the Large Hadron Collider would reveal itself as a resonance in the expected smooth distribution of the top-antitop quark invariant mass. This thesis presents a search for such a new heavy particle decaying to a pair of top-antitop quarks in the semi-leptonic final state. The analyzed data sample amounts to a total of 4.6 fb−1 at a proton-proton collision center-of-mass energy of 7 TeV. Novel techniques specifically tailored to the identification of the decay products of highly energetic top quarks are developed and used. No evidence for resonant production of pairs of top-antitop quarks is found and, as a result, constraints are set on two theoretical models. Upper limits on the production cross-section times branching ratio are established at a 95% credibility level for a leptophobic Z′ boson from the Topcolor model, and a Kaluza-Klein gluon from the Randall-Sundrum model. The Z′ boson and the Kaluza-Klein gluon are excluded to exist (at a 95% credibility level) in the mass ranges 0.8-1.65 TeV and 0.8-1.88 TeV, respectively. The constraints de- rived in this thesis on the two theoretical models are more stringent than the ones obtained at other experiments, thanks to the large center-of-mass energy and the dedicated high-energy top quark identification techniques used.La nature intrigante du quark top, de loin la particule élémentaire la plus lourde du Modèle standard de la physique des particules, a motivé le développement de nom-breuses théories prédisant l'existence de nouvelles particules massives se désintégrant en une paire de quarks top-antitop. La production de ces particules hypoth étiques dans des collisions de type proton-proton au Grand collisionneur de hadrons (LHC) se manifesterait sous la forme d'une résonance dans la distribution de la masse invariante des paires de quarks top-antitop. La présente thèse consiste en une recherche d'une telle particule se désintégrant en une paire de quarks top-antitop dans l'état final dit semi-leptonique. La taille de l'échantillon de données analysé équivaut à 4.6 fb−1 à une énergie de centre de masse des collisions proton-proton de 7 TeV. Des techniques novatrices d'identification des produits de désintégrations de quarks top à grande énergie sont développées et utilisées. La présence d'une résonance dans la production de paires de quarks top-antitop n'a pu être établie et, conséquemment, des contraintes sont dérivées sur deux modèles théoriques. Des limites supérieures sur la section efficace de production multipliée par le rapport de branchement sont établies avec un niveau de crédibilité de 95% pour un boson Z′ leptophobique du modèle Topcolor, ainsi que pour un gluon Kaluza-Klein du modèle Randall-Sundrum. Le boson Z′ et le gluon Kaluza-Klein sont proscrits (avec un niveau de crédibilité de 95%) dans la région de masse 0.8-1.65 TeV et 0.8-1.88 TeV respectivement. Grâce à la grande énergie de centre de masse ainsi qu'aux techniques spécialisées d'identification des quarks top de grande énergie, les contraintes dérivées dans la présente thèse sur les deux modèles théoriques ici considérés sont plus restrictives que celles obtenues par le biais d'autres expériences.
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Falla, R. J. "Search for Higgs boson pair production in the bƃbƃ final state at the Large Hadron Collider." Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1482160/.
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The work presented in this thesis focuses on the search for resonant and non-resonant Higgs boson pair production in the bƃbƃ final state at the LHC. All of the searches require the use of high transverse momentum b-tagged jet systems. The first search presented is performed using a dataset of proton- proton collisions at √s = 8 TeV, collected in 2012 with the ATLAS detector, corresponding to an integrated luminosity of 19.5 fb^{-1}. The Higgs boson decay products are reconstructed as a pair of close- by small radius b-tagged jets with a high transverse momentum, known as "dijets". The resonant signals looked for are a Randall- Sundrum Kaluza-Klein graviton, G^*, and a heavy neutral scalar boson in the 2HDM model, H. A non-resonant search is also performed. No evidence for resonant or non-resonant Higgs boson pair production is observed. An upper limit on the cross-section for σ(pp → G^* →hh→bƃbƃ) of 3.2 fb is set for a G^* mass of 1.0 TeV, at the 95% confidence level. The search for non-resonant Standard Model hh production sets an observed 95% confidence level upper limit on the production cross-section σ(pp → hh → bƃbƃ) of 202 fb, compared to a SM prediction of σ(pp → hh → bƃbƃ) = 3.6 ± 0.5 fb. In preparation for Run 2 and the HL-LHC simulation studies based on √s = 14 TeV are made. A non-resonant search using the dijet method used in Run 1 is presented. A resonant study is also presented which shows a new method for reconstructing pp → X →hh→bƃbƃ events. It uses the combination of many Higgs boson reconstruction techniques which vary with the Higgs boson transverse momentum and is shown to be excellent at providing a high signal efficiency.
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Livermore, Sarah Stephanie Alexandra. "A search for massive top quark resonances with the ATLAS detector at the Large Hadron Collider." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:c826ed7f-1566-4a93-8675-d32ed3b97f7d.
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This thesis presents a search for resonant production of top-antitop quark pairs in final states containing at least one electron or muon. A number of beyond the standard model (BSM) theories incorporate a specific role for the top quark, resulting in resonances that preferentially decay to t(bar over t) pairs. The data sample analysed corresponds to an integrated luminosity of 2.05 fb-1 recorded during 2011 using the ATLAS detector at the Large Hadron Collider. The proton-proton centre-of-mass energy was 7 TeV. The search is tailored towards heavy resonances at the TeV-scale which therefore decay to top quarks with high transverse momentum. Large hadronic jets are used to reconstruct the energy carried by the hadrons and the substructure of these jets is studied in order to identify hadronically decaying top quarks. The reconstruction can therefore proceed even if the decay products of the top quark are highly collimated. This study represents the first use of jet substructure techniques in a search for t(bar over t) resonances using hadron-hadron collision data. The invariant mass of the reconstructed t(bar over t) pair is used to test compatibility of the data with the standard model prediction. No evidence for t(bar over t) resonances is found. Upper limits are derived on the production cross-section times branching ratio for narrow and wide resonant states, at the 95 % credibility level. An upper limit of 0.61 (0.65) pb is set for a narrow (wide) resonance with a mass of 1 TeV. Two specific BSM models are excluded within certain mass ranges: the narrow leptophobic Z' boson with mass 600 - 1150 GeV and the wide Kaluza-Klein gluon with a mass below 1.5 TeV. These results represent a significant improvement on those of previous searches performed at the ATLAS experiment, which did not use jet substructure techniques. In addition, the possibility of using jets which decrease in size as their transverse momentum increases is investigated using simulated data. The yield of events due to resonant t(bar over t) production increases by approximately 20 % compared to when using jets of fixed size. Furthermore, the resolution of the invariant mass of the reconstructed t(bar over t) pair is found to improve by almost one fifth. It is recommended that a calibration scheme be developed for these variable-sized jets, so that their potential to improve the sensitivity to t(bar over t) resonances can be investigated further.
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Tua, Alan. "Search for supersymmetry using heavy flavour jets with the ATLAS detector at the Large Hadron Collider." Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/3697/.
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The Standard Model of particle physics, despite being extremely successful, is not the ultimate description of physics. The nature of dark matter is not well described, unification of the forces is not achieved and the theory is plagued by a hierarchy problem. One of the proposed solutions to these issues is supersymmetry. This thesis describes numerous searches for supersymmetry carried out using the ATLAS detector at the Large Hadron Collider. In scenarios where R-parity is conserved, supersymmetric final states contain large amounts of missing transverse energy. Furthermore, should supersymmetry correctly describe Nature, the scalar partners of the third generation quarks might be the lightest scalar quarks. The searches reported here exploit these possibilities and make use of signatures which are rich in missing transverse energy and jets coming from heavy flavour quarks. Searches are carried out for direct pair production of third generation scalar quarks as well as gluino-mediated production of these particles. A data driven technique to estimate the backgrounds coming from multijet production is described and shown to work in analyses targeting heavy flavour quarks. No significant excesses are observed in a number of analyses. In each case limits are set on the allowed masses of supersymmetric particles in a variety of phenomenological models and in specific supersymmetry breaking scenarios.
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Tylmad, Maja. "Search for Weakly Produced Supersymmetric Particles in the ATLAS Experiment." Doctoral thesis, Stockholms universitet, Fysikum, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-108060.
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The Large Hadron Collider located at CERN is currently the most powerful particle accelerator and ATLAS is an experiment designed to exploit the high energy proton-proton collisions provided by the LHC. It opens a unique window to search for new physics at very high energy, such as supersymmetry, a postulated symmetry between fermions and bosons. Supersymmetry can provide a solution to the hierarchy problem and a candidate for Dark Matter. It also predicts the existence of new particles with masses around 1 TeV, thus reachable with the LHC. This thesis presents a new search for supersymmetry in a previously unexplored search channel, namely the production of charginos and neutralinos directly decaying to electroweak on-shell gauge bosons, with two leptons, jets, and missing transverse momentum in the final state. The search is performed with proton-proton collision data at a center of mass energy of √s = 8 TeV recorded with the ATLAS experiment in 2012. The design of a signal region sensitive to the new signal is presented and a data driven technique to estimate the Z+jets background is developed. Precise measurements of hadronic jet energies are crucial to search for new physics with ATLAS. A precise energy measurement of hadronic jets requires detailed knowledge of the pulse-shapes from the hadron calorimeter signals. Performance of the ATLAS Tile Calorimeter in this respect is presented using both pion test-beams and proton–proton collision data.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2 and Paper 4: Technical report from the ATLAS experiment.
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Marsden, Stephen Philip. "Search for diboson resonance production at sqrt(s) = 8 TeV with the ATLAS detector." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/search-for-diboson-resonance-production-at-sqrts--8-tev-with-the-atlas-detector(91f7ac80-2f2a-4c75-a21c-00063c527947).html.
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A search for heavy exotic diboson resonances decaying to llqq final states is presented using pp collision data collected with the ATLAS detector at the Large Hadron Collider. The analysis uses a data sample corresponding to an integrated luminosity of 20.3 fb^-1 at sqrt(s) = 8 TeV collected between April and December 2012. No significant excess of data events over the predicted Standard Model background is observed and 95% confidence level upper limits are set on the product of the production cross-section and the branching ratio for spin-2 Kaluza-Klein gravitons predicted by the bulk Randall-Sundrum model and for Extended Gauge Model W’ bosons. These results are subsequently combined with limits obtained from searches using the lvll, lvqq, and qqqq final states, and new mass limits are set on both signal models.
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Gregson, Samuel John. "Search for CP violation in charged D decays at the LHCb experiment." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708922.
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De, Lorenzo Gianluca. "Search for the Production of Gluinos and Squarks with the CDF II Experiment at the Tevatron Collider." Doctoral thesis, Universitat Autònoma de Barcelona, 2010. http://hdl.handle.net/10803/3423.
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Según la teoría de súper-simetría, gluinos y squarks son la versión súper-simétrica de quarks y gluones del modelo estándar. Tanto en el Tevatron como en el LHC, el canal de física con la mayor sensibilidad a la posible presencia de partículas súper-simétricas en el estado final corresponde a la producción inclusiva de gluinos y squarks (la versión súper-simétrica de quarks y gluones) gracias a la presencia de acoplos fuertes en los diagramas relevantes (véase figura 3). Procesos inclusivos producen señales características en los detectores, con la presencia de múltiples jets de hadrones y una gran energía transversa faltante.
Estas topologías corresponden a la producción de gluinos y squarks que decaen en múltiples quarks y gluones. Cuando se impone la conservación de R-Parity, a presencia de neutralinos estables (LSPs) en el estado final, que abandonan el detector, produce la señal de energía transversa faltante.
Esta Tesi incluye dos búsquedas de la producción de gluinos y squarks en entre protones y anti-protones con una energía en el centro de masas de 1.96 TeV con el experimento CDF II en el Tevatron de Chicago. La primera es la búsqueda inclusiva de gluinos y squarks y la secunda es la búsqueda de de una posible producción de squarks sbottom.
La tesi esta organizada como sigue: el capitulo 1 es una introducción a la teoría de súper-simetría; el capitulo 2 describe el Tevatron y el experimento CDF II; los capítulos 3 y 4 incluyen los detalles sobre las dos búsquedas. Finalmente, las conclusiones están en el capitulo 5.
According to the theory of Supersymmetry, squarks and gluinos are the supersymmetric partners of the Standard Model quarks and gluons. In the phenomenological framework assumed for this Thesis, squarks and gluinos are produced in pairs and ultimately decay into multiple partons and neutralinos, the lightest of the supersymmetric particles. The neutral and weakly interacting neutralinos escape the detector undetected. As a result, the final state is characterized by multiple jets of hadrons and large missing transverse energy.
This Thesis reports on two searches for the production of gluinos and squarks in proton-antiproton collisions at a center of mass energy of √s = 1.96 GeV with the CDF Run II experiment at the Tevatron collider. The first of the two analyses is an inclusive search for gluinos and squarks while the second one is dedicated to the search for direct pair production of sbottom squarks. The Thesis is organized as follows: Chapter 1 presents a brief introduction to Supersymmetry; Chapter 2 describes the Tevatron collider and the CDF II experiment; Chapter 3 and 4 are dedicated to the inclusive search for squarks and gluinos, and the exclusive search for sbottom squarks, respectively. Finally, Chapter 5 is devoted to conclusions.
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Khoo, Teng Jian. "The hunting of the squark : experimental strategies in the search for supersymmetry at the Large Hadron Collider." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/244670.
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In its first three years of operation, the Large Hadron Collider at CERN has already proved its worth as a discovery machine and reinvigorated the prospects for discovering new dynamics beyond the Standard Model. This thesis presents a range of experimental methods devised for discovery of supersymmetry, one of the most important extensions of the Standard Model being tested at the LHC. The first chapter discusses the concepts behind a set of transverse mass-bound variables, and explores connections between these variables and others in the literature. Not only are these variables important tools for mass measurement, should sparticles be seen at the LHC, they are also critical components of experimental searches. Accordingly, their performance has been compared in both mass measurement and search contexts, and the results are reported here. This is followed by the details of a search for hadronically-decaying squarks and gluinos, carried out on 4.7 fb−1 of data collected at 7 TeV in 2011 by the ATLAS detector. The search strategy is described, focusing on the implementation of a background estimation method using photon events to determine the background contamination due to invisible Z boson decays. The results of the search are then presented. Stringent limits are set on the production of squarks and gluinos in a variety of model scenarios.
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Zhu, Hongbo. "Photon conversion reconstruction and its application to the Higgs search in Atlas experiment at the Large Hadron Collider." Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.511997.
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Oksuzian, Yuri. "Search for resonant production of top antitop pairs decaying into multi-jets at the collider detector at Fermilab." [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0041141.
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Abulaiti, Yiming. "Search for Pair-Produced Supersymmetric Top Quark Partners with the ATLAS Experiment." Doctoral thesis, Stockholms universitet, Fysikum, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-132289.
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Searches for the supersymmetric partner of the top quark (stop) are motivated by natural supersymmetry, where the stop has to be light to cancel the large radiative corrections to the Higgs boson mass. This thesis presents three different searches for the stop at √s = 8 TeV and √s = 13 TeV using data from the ATLAS experiment at CERN’s Large Hadron Collider. The thesis also includes a study of the primary vertex reconstruction performance in data and simulation at √s = 7 TeV using tt and Z events. All stop searches presented are carried out in final states with a single lepton, four or more jets and large missing transverse energy. A search for direct stop pair production is conducted with 20.3 fb−1 of data at a center-of-mass energy of √s = 8 TeV. Several stop decay scenarios are considered, including those to a top quark and the lightest neutralino and to a bottom quark and the lightest chargino. The sensitivity of the analysis is also studied in the context of various phenomenological MSSM models in which more complex decay scenarios can be present. Two different analyses are carried out at √s = 13 TeV. The first one is a search for both gluino-mediated and direct stop pair production with 3.2 fb−1 of data while the second one is a search for direct stop pair production with 13.2 fb−1 of data in the decay scenario to a bottom quark and the lightest chargino. The results of the analyses show no significant excess over the Standard Model predictions in the observed data. Consequently, exclusion limits are set at 95% CL on the masses of the stop and the lightest neutralino.
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Clark, Brian. "A Search for New Resonant Phenomena in Dijet Final States With the ATLAS Detector at the Large Hadron Collider." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493365.
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This dissertation describes a model-agnostic search for new resonant phenomena decaying to two jets (dijets) in 3.6 fb-1 of proton-proton collisions at center-of-mass energy sqrt(s)=13 TeV. The collisions were produced by the Large Hadron Collider and recorded by the ATLAS detector in 2015. A dijet invariant mass spectrum is examined for local excesses above a data-driven background estimation accounting for Standard Model production. No statistically significant excess is observed. New physics models are excluded at 95% credibility-level for quantum black holes with production mass thresholds below 5.3 TeV, 8.1 TeV, and 8.3 TeV for three different production scenarios and for excited quarks of masses less than 5.2 TeV. Furthermore, limits are provided on generic Gaussian signal shapes for additional generalization of the 2015 dijet resonant analysis search results.Physics
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Brinson, Jessica. "A search for disappearing tracks in proton-proton collisions at sqrt(s) = 8 TeV." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1428940893.
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Ji, Weifeng. "Search for the decays of stopped exotic long-lived particles produced in P-P collisions at 13 TeV at CMS." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524216345344165.
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Hart, Andrew Evan. "Search for disappearing tracks in proton-proton collisions at √s = 13 TeV." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1517587469347379.
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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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Shcherbakova, Anna. "Calibration of b-tagging and search for Dark Matter : Calibration of b-tagging efficiency and search for Dark Matter production in association with heavy flavour quarks with the ATLAS experiment." Doctoral thesis, Stockholms universitet, Fysikum, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-146034.
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The Large Hadron Collider (LHC) is the most powerful and complex particle accelerator ever built. The ATLAS and the CMS are the two multipurpose particle detectors at the LHC, designed to cover a wide range of physics measurements. Three physics studies performed using data of proton-proton collisions collected with the ATLAS detector are presented. The identification of jets originating from b quarks, also known as b-tagging, is a crucial tool for many physics analyses at the LHC. This thesis presents a calibration of the b-tagging efficiency for high transverse momentum jets using a new calibration technique. This analysis is based on template fits and uses multi-jet events, which allows to perform the calibration for jets with transverse momenta up to 1200 GeV. This thesis also describes a completed and connected technical project on the development of the b-tagging ATLAS software. Dark Matter (DM) is a new phenomenon introduced to explain astrophysical observations. The nature of DM is one of the most important subjects of investigations in the modern physics, and many of these investigations are carried out at the LHC. A search for DM production in association with a pair of heavy flavour quarks has been recently performed in ATLAS at a centre-of-mass energy √s = 8 TeV under the Effective Field Theory approach. A re-interpretation of the results of this search under assumption of the simplified models is presented. A set of simplified models is considered with various DM masses, masses of the spin-0 exchange particle, that mediates the interaction between DM and the regular matter, and various values of couplings. Benchmark models are chosen to be used in the DM searches at √s = 13 TeV. The last part of the thesis presents a search for DM production in association with a pair of top quarks performed under assumption of the simplified models with spin-0 mediator, using the data collected at a centre-of-mass energy √s = 13 TeV. The observed data are shown to be in good agreement with the Standard Model predictions, and upper limits are set on a ratio between the observed DM production cross section and the value expected by the simplified model.
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Santoyo, Castillo Itzebelt. "Search for supersymmetry in final states with three leptons and missing transverse energy with the ATLAS detector at the Large Hadron Collider." Thesis, University of Sussex, 2015. http://sro.sussex.ac.uk/id/eprint/54337/.
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The ATLAS experiment at the Large Hadron Collider has collected an unprecedented amount of data in the 3 years of data taking since its start. In this document I will discuss the results of the analysis I performed during my PhD at the university of Sussex for the search of Supersymmetry in events with three leptons (electron/muon/tau) and missing transverse energy in the final state. The search is performed on the full dataset collected by the experiment in 2012, at a centre-of-mass energy of 8 TeV. These results are interpreted in SUSY models with chargino-neutralino pair production via decays involving sleptons, staus, gauge bosons and the newly discovered Higgs boson. These results presented improve on previous searches performed at ATLAS in three lepton final states with only electrons and muons. Special focus will be given to the optimisation process of Supersymmetry signal with respect to the SM background, and the statistical interpretation of the results obtained with this search.
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Readioff, N. P. "Search for resonances decaying to a Z boson and a photon in the ATLAS Detector using data from the Large Hadron Collider." Thesis, University of Liverpool, 2016. http://livrepository.liverpool.ac.uk/3004762/.
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This thesis presents a search for Zγ resonances in the context of both the Standard Model Higgs boson and exotic high mass particles. The search for evidence of a Standard Model Higgs boson undergoing the decay H→Zγ, Z→ll, where l = e or μ, is performed using proton-proton collision data recorded by the ATLAS detector at the LHC corresponding to 4.5 fb⁻¹ at a centre-of-mass energy √s = 7 TeV and 20.3 fb⁻¹ at a centre-of-mass energy √s = 8 TeV. No significant excess over the Standard Model prediction is observed and so exclusion limits on the production cross-section of an SM Higgs boson decaying to Zγ are set at 95% confidence level: production of the Higgs boson at 9.0 x SM predictions is excluded. Refinements to the analysis are presented, making use of an alternative event classification based on the mass of the reconstructed Z boson to increase the sensitivity and set improved exclusion limits: production of the Higgs boson at 8.0 x SM predictions is excluded. A search for a new Higgs-like boson, X, with high mass and decaying through Zγ to an llγ final state, where l = e or μ, is performed using proton-proton collision data recorded by the ATLAS detector at the LHC corresponding to 3.2 fb⁻¹ at a centre-of-mass energy √s = 13 TeV. No significant excesses above the SM background are observed and so exclusion limits at 95% confidence level are set on the production cross section times decay branching ratio to Zγ for such a boson with mass between 250 GeV and 1.5 TeV.
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Edwards, Clive. "Search for the Higgs Boson in the process H→ZZ→llνν produced via vector-Boson fusion with the ATLAS detector." Thesis, Royal Holloway, University of London, 2012. http://repository.royalholloway.ac.uk/items/79b35bf5-8305-672c-108f-4f701dfeca56/9/.
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The search potential of a Standard Model Higgs boson in the Vector Boson Fusion production mechanism with Higgs boson decaying to two leptons and two neutrinos via decay to two Z bosons with the ATLAS detector is investigated. The ATLAS detector is a general purpose detector in operation at CERN measuring proton-proton collisions produced by the Large Hadron Collider. This channel has been shown to have high sensitivity at large Higgs mass, where large amounts of missing energy in the signal provide good discrimination over expected backgrounds. This work takes a first look at whether the sensitivity of this channel may be improved using the remnants of the vector boson fusion process to pro- vide extra discrimination, particularly at lower mass where sensitivity of the main analysis is reduced because of lower missing energy. Simulated data samples at centre of mass energy 7 Te V are used to derive signal significances over the mass range between 200-600 Ge V / c2. Because of varying signal properties with mass, a low and a high mass event selection were developed and optimized. A comparison between simulated and real data (collected in 2010) is made of variables used in the analysis and the effect of pileup levels corresponding to those in the 2010 data is investigated. Possible methods to estimate some of the main backgrounds to this search are described and discussed. The impact • of important theoretical and detector related systematics are taken into account. Final results are presented in the form of 95 % Confidence Level exclusion limits on the signal cross section relative to the SM prediction as a function of Higgs boson mass, based on an integrated luminosity of 33.4 pb -1 of data collected during 2010.
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Ducu, Otilia-Anamaria. "Search for new physics in events with same sign leptons and missing energy with ATLAS at LHC." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4053/document.
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Dans les études présentées ici, seules les données collectées par le détecteur ATLAS sont analysées. La première partie du document décrit en détails le contexte théorique sous-jacent à ces études, ainsi que lecolllisioneur LHC et l'expérience ATLAS. Le LHC étant un collisionneur hadronique, l'identification et la reconstruction des leptons est cruciale pour les mesures précises de section efficaces des processus du Modèle Standard, ou la recherche de nouvelle physique. C'est pourquoi la deuxième partie du document est dédiée aux mesures de performances : mesures in situ des efficacités de reconstruction et d'identification des électrons. La recherche de nouvelle physique est présentée dans la troisième partie du document. Cette étude a été réalisée dans le canal incluant deux leptons de même charge et de l'énergie transverse manquante. Les résultats inclus ont été obtenus avec un ensemble de données collectées à $sqrt s$ = 8 TeV correspondant à une luminosité intégrée de L = 20 fb$^{-1}$, ainsi que les premières données collectées avec $sqrt s$ = 13 TeV. L'état final constitué d'une paire de leptons de même charge et de jets permet également la mesure directe du couplage de Yukawa pour le quark top, à l'aide du processus $ppto tbar tH$. Ce couplage est le plus élevé dans le Modèle Standard et associe les deux particules élémentaires les plus lourdes prédites par la théorie, le quark top et le boson de Higgs. Dans la quatrième partie de ce document, une étude complète de la sensibilité pouvant être atteinte avec une énergie de $sqrt s$ = 13TeV et une luminosité intégrée de 100 fb$^{-1}$ of data, est présentée pour le canal incluant deux leptons de même chargeFor the presented studies only the data recorded with the ATLAS detector is analyzed. The theoretical framework, the LHC collider and the ATLAS experiment are given in the first part of this thesis.At hadron colliders, the lepton identification and reconstruction are crucial for precise SM cross sections and coupling measurements or for new physics searches. Therefore, the second part of my thesis is dedicated to performance studies : in-situ measurements of electron identification and reconstruction efficiencies. The search for new physics is presented in the third part of the thesis. For these studies the channel with two same~- sign leptons and missing transverse energy is considered. The results are obtained with $L$~=~20 fb$^{-1}$ of data recorded at $sqrt s$ = 8 TeV and with the very first data at $sqrt s$ = 13 TeV. At the end of Run-1 no significant excess in data over the Standard Model prediction is observed and stringent limits on the supersymmetric particle masses are set. With the two same - sign leptons and jets final state it is also possible to measure directly the top quark Yukawa coupling using the ttbar + $H$ channel. This coupling is the largest in the Standard Model and it connects two of the heaviest particles predicted by the Standard Model, the top quark and the Higgs boson. In the fourth part of this thesis, a complete optimization is performed to reach the highest sensitivity for this signal in the two same~- sign leptons channel at $sqrt s$ = 13 TeV with 100 fb$^{-1}$ of data, corresponding to the end of Run-2
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Nattermann, Till [Verfasser]. "Search for Supersymmetry with Tau Leptons, Muons, Missing Transverse Momentum and Jets with the ATLAS Experiment at the Large Hadron Collider / Till Nattermann." Bonn : Universitäts- und Landesbibliothek Bonn, 2013. http://d-nb.info/1044972017/34.
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