Despite advances in multivariate visualisations and computer graphics, allowing for effective implementations, most particle physics analyses still rely on conventional data visualisations. The currently available software implementing these techniques has been found to be inadequate for use with the large volume of multivariate data produced from modern particle physics experiments. After a design and development period, a novel piece of software, DataViewer, was produced. DataViewer was used as part of a physics analysis at the CMS experiment, searching for an associated Higgs decaying through a dark sector into collimated groups of electrons, called Electron Jets. Observation of such a signature could explain astrophysical anomalies found by numerous telescopes. The full 2011 dataset, equivalent to an integrated luminosity of 4.83 fb^(-1) at a centre of mass energy of sqrt(s) = 7 TeV, recorded by the experiment was analysed. DataViewer was found to be extremely powerful in rapidly identifying interesting attributes of the signature which could then be exploited in the analysis. Additionally it could be used for cross checking other complex techniques, including multivariate classifiers. No evidence was found for the production of a Higgs boson in association with a Z boson, where the Higgs subsequently decays to Electron Jets. Upper limits on the production of benchmark models were set at the 95% Confidence Level.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21563号 / 理博第4470号 / 新制||理||1641(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 中家 剛, 教授 鶴 剛, 准教授 吉岡 興一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

The Standard Model (SM) is the theoretical framework that describes the state of the art in particle physics. It has been extremely successful at describing the particles and forces observed in nature. However, the theory is known to be incomplete. Among other things, it cannot explain dark matter, the dynamics of electroweak symmetry breaking, neutrino masses, nor how gravity is to be incorporated into its framework. A popular extension of the SM introduces a new particle similar to a W boson, typically called a W' boson. Other classes of theories, such as technicolor, offer alternatives to the SM's implementation of electroweak symmetry breaking and predict, among others, a new particle called technirho. The new particles introduced by these extensions are expected to decay into WZ boson pairs. This final state provides a distinctive search signal. This dissertation describes a search for these exotic new particles decaying via WZ pairs to a leptonic ( l+l-l'v, with l, l' = e, u) final state. The data was collected with the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider at CERN (European Organization for Nuclear Research). Data from 5 /fb of proton-proton collisions taken at a center of mass energy of 7 TeV in 2011 and 20 /fb taken at a center of mass energy of 8 TeV in 2012 were analyzed. No significant excess over the expected Standard Model background was observed and 95% confidence level upper exclusion limits were placed on the production cross section. These were interpreted as mass exclusion limits in the common benchmark of the Sequential Standard Model (SSM) and low-scale technicolor. Assuming the SSM, W' masses between 170 and 1450 GeV were excluded. Limits were also set on the mass of the technirho under a range of scenarios. These are the strongest limits to date in this channel.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Although astrophysical evidence supports the existence of dark matter (DM), it remains one of the unanswered questions left by the Standard Model (SM) of Particle Physics. However, under hypotheses of new interactions, the production of dark matter can be detected as an excess of events with large missing transverse momentum (p_T^miss) over the SM background process. This thesis documents a search for new particles at the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC), targeting events where large p_T^miss and energetic jets are produced in a proton-proton collision at 13 TeV. The data were collected from 2017 to 2018 during the second half of LHC Run-II. The analysis also targets events where a jet is produced from W or Z bosons identified by a deep-neural-network-based tagger. Multiple control regions targeting specific background processes are defined which estimate background yield in the signal region through a simultaneous fit across control regions of all search channels. The result for the Run-II data corresponding to an integrated luminosity of 137 fb^-1 is obtained by combining this analysis with the previously published 2016 data. No excess of events is observed compared to the SM background expectations. The result of this search is interpreted in several new physics models, including simplified dark matter models, large extra dimension model (ADD), Higgs portal models, and leptoquark models. Limits are set on model parameters providing the most stringent direct constraints on dark matter search from colliders.

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This thesis presents a search for Supersymmetry in final states containing two same-flavor opposite-sign leptons, jets and large missing transverse momentum. The search makes use of 36.1 fb−1 of proton-proton collision data collected at a center-of-mass energy of √s = 13 TeV by the ATLAS detector at the Large Hadron Collider. Two signal scenarios, which both involve the pair-production of squarks or gluinos decaying into final states with two leptons and the lightest supersymmetric particle, are targeted by the analysis. The first scenario considers decay chains with a leptonically decaying Z boson and is characterized by a peak in the dilepton invariant mass distribution. In the second scenario, decays through intermediate sleptons or an off-shell Z boson are considered. Such processes lead to a kinematic endpoint in the dilepton invariant mass distribution. The main Standard Model backgrounds include the pair-production of top quarks and direct production of Z bosons. These backgrounds are estimated with two data-driven methods. The observed data is found to be consistent with the Standard Model expectation and the results are interpreted in simplified Supersymmetry models for gluino and squark pair-production. Sensitivity is provided for gluino and squark masses up to 1.85 TeV and 1.3 TeV respectively. / I denna avhandling presenteras en analys som letar efter supersymmetriska partiklar producerade i proton-proton-kollisioner vid en kollisionsenergi på √s = 13 TeV. Analysen använder sig av data insamlad under 2015 och 2016 av ATLAS-experimentet vid CERNs Large Hadron Collider. Den totala analyserade datamängden motsvarar 36,1 fb−1. Kollisioner som resulterar i par av elektroner eller myoner med motsatt laddning, jets och en stor obalans i rörelsemängd i det transversella planet väljs ut för analys. Målet är att finna tecken på en produktion av skvarkar eller gluiner som sönderfaller till två leptoner och en oladdad supersymmetrisk partikel som lämnar detektorn utan att lämna någon signal. Inom supersymmetriska modeller kan sådana slutliga tillstånd uppkomma genom sönderfallskedjor med Z-bosoner som sönderfaller leptoniskt, eller genom sönderfallskedjor med sleptoner. Flera processer som förutspås av Standardmodellen kan efterlikna den eftersökta signalen och utgör bakgrunder i analysen. De viktigaste bakgrunderna består av Z-bosoner och par av toppkvarkar som produceras direkt i proton-proton-kollisionerna. Dessa bakgrunder uppskattas genom att använda data, medan andra mindre bakgrunder uppskattas genom att använda simuleringar. Ingen signifikant signal utöver den uppskattade backgrunden uppmäts i analysen. Istället tolkas resultaten med hjälp av simuleringar av förenklade supersymmetriska modeller. På så sätt kan exkluderingsgränser med 95% konfidensnivå beräknas för gluino- och skvark-massorna. Massor över 1,85 TeV utesluts för gluiner och massor över 1,3 TeV utesluts för skvarkar. / <p>QC 20180109</p>

In the context of an intensive upgrade plan for the Large Hadron Collider (LHC) in order to provide proton beams of increased luminosity, a revision of the data readout electronics of the Liquid-Argon-Calorimeter of the ATLAS detector is scheduled. This is required to retain the efficiency of the trigger at increased event rates despite its fixed bandwidth. The focus lies on the early digitization and finer segmentation of the data provided to the trigger. Furthermore, there is the possibility to implement new energy reconstruction algorithms which are adapted to the specific requirements of the trigger. In order to constitute crucial design decisions, such as the digitization scale or the choice of digital signal processing algorithms, comprehensive simulations are required. High trigger efficiencies are decisive at it for the successful continuation of the measurements of rare StandardModel processes as well as for a high sensitivity to new physics beyond the established theories. It can be shown that a significantly improved resolution of the missing transverse energy calculated by the trigger is achievable due to the revised segmentation of the data. Various energy reconstruction algorithms are investigated in detail. It can be concluded that these will facilitate reliable trigger decisions for all expected working conditions and for the whole possible energy range.