1,721,096 research outputs found
ttH Coupling Measurement with the ATLAS Detector at the LHC
No full textThe Higgs boson is discovered on the 4th of July 2012 with a mass around 125 by ATLAS and CMS experiments at LHC. Determining the Higgs properties (production and decay modes, couplings,...) is an important part of the high-energy physics programme in this decade. A search for the Higgs boson production in association with a top quark pair (ttH) at ATLAS is presented in this talk at an unexplored center-of-mass energy of 13 TeV, which could allow a first direct measurement of the top quark Yukawa coupling and could reveal new physics. The ttH analysis in ATLAS is divided into 3 channels according to the Higgs decay modes: Hadrons, Leptons and Photons. The best-fit value of the ratio of observed and Standard Model cross sections of ttH production process, using 2015-2016 data and combining all ttH final states, is 1.8 0.7, corresponds to 2.8 (1.8 ) observed (expected) significance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Search for Higgs boson production in association with a top quark pair in two same-sign lepton final states with the ATLAS detector at LHC
No full textThe Large Hadron Collider (LHC) at CERN restarted in spring 2015 for three years (Run2) at an unexplored center-of-mass energy of 13 TeV; An ideal place to search for physics beyond the Standard Model such as supersymmetry (SUSY) and extra dimensions. A precise measurement of electron reconstruction efficiency in ATLAS, one of the two general purpose experiments of the LHC, is presented in the first part of this thesis with data sample using 3.2 of data recorded in 2015. This allows to extract scale factors between data and simulation that are used by all ATLAS physics analyses involving electrons. The results show the high ability of the ATLAS detector to reconstruct electrons from one hand and the good understanding of its performance on the other hand. The second part of the thesis is dedicated to a search for the Higgs boson production in association with a top quark pair (), which could allow a first direct measurement of the top quark Yukawa coupling and could reveal new physics. The signature with two same-charge light leptons (electron or muon) without a hadronically decaying tau lepton final state, targeting the decays , is examined using the first 10% of the total expected Run2 dataset. Events with fake (non-prompt) leptons represent the main reducible background of this signature. The estimation of this background largely drives the signal sensitivity. An improved method to estimate it has been developped and is discussed in details in this thesis. Driving the total error, fake leptons background is found to be 1.5 to 3.6 times higher than in simulation and represent between 32 and 48% of the total background. The best-fit value of the ratio of observed and Standard Model cross sections of production process, combining with other multilepton channels, is 2.5 0.7 (stat) (syst), and an upper limit on this ratio of 4.9 (2.3 expected) is found at 95% confidence level
Recherche de la production du boson de Higgs en association avec une paire de quarks top dans les canaux avec deux leptons de même charge à partir du detecteur ATLAS au LHC
No full textThe Large Hadron Collider (LHC) at CERN restarted in spring 2015 for three years (Run2) at an unexplored center-of-mass energy of 13 TeV; An ideal place to search for physics beyond the Standard Model such as supersymmetry (SUSY) and extra dimensions. A precise measurement of electron reconstruction efficiency in ATLAS, one of the two general purpose experiments of the LHC, is presented in the first part of this thesis with Z→ee data sample using 3.2 fb−1 of data recorded in 2015. This allows to extract scale factors between data and simulation that are used by all ATLAS physics analyses involving electrons. The results show the high ability of the ATLAS detector to reconstruct electrons from one hand and the good understanding of its performance on the other hand. The second part of the thesis is dedicated to a search for the Higgs boson production in association with a top quark pair (tt¯H), which could allow a first direct measurement of the top quark Yukawa coupling and could reveal new physics. The signature with two same-charge light leptons (electron or muon) without a hadronically decaying tau lepton final state, targeting the decays H→ WW⋆, is examined using the first 10% of the total expected Run2 dataset. Events with fake (non-prompt) leptons represent the main reducible background of this signature. The estimation of this background largely drives the signal sensitivity. An improved method to estimate it has been developped and is discussed in details in this thesis. Driving the total error, fake leptons background is found to be 1.5 to 3.6 times higher than in simulation and represent between 32 and 48% of the total background. The best-fit value of the ratio of observed and Standard Model cross sections of tt¯H production process, combining with other multilepton channels, is 2.5± 0.7 (stat) +1.1−0.9 (syst), and an upper limit on this ratio of 4.9 (2.3 expected) is found at 95% confidence level.Le Grand Collisionneur de Hadrons (Large Hadron Collider, LHC) du CERN a redémarré au printemps 2015 pour trois ans (Run 2) avec une énergie dans le centre de masse de 13 TeV, idéale pour la recherche de physique au delà du Modèle Standard, comme la Supersymétrie ou des dimensions supplémentaires. Une mesure précise de l’efficacité de reconstruction des électrons avec le détecteur ATLAS, une des deux expériences généralistes présentes au LHC, est présentée dans la première partie de cette thèse en utilisant les 3.2 f b −1 de données récoltées au cours de l’année 2015 en étudiant le canal de désintégration Z → ee. Cela a permis d’extraire les rapports d’efficacité de reconstruction des électrons obtenus avec les données et la simulation, lesquels sont utilisés par toutes les analyses d’ATLAS impliquant des électrons. Les résultats montrent d’une part une grande efficacité de reconstruction des électrons avec le détecteur ATLAS, et une bonne compréhension de ses performances d’autre part. La seconde partie de ce manuscrit est dédiée à la recherche de la production associée du boson de Higgs avec une paire de quarks top (t t ̄ H), qui pourrait permettre une première mesure directe du couplage de Yukawa entre le boson de Higgs et le quark top. Une déviation dans la mesure par rapportaux prédictions du Modèle Standard serait une preuve manifeste de Nouvelle Physique. La signature de l’état final avec deux leptons de même charge électrique (électrons ou muons) est examinée en utilisant les premiers 10% du total de données attendues pour le Run 2, portant l’attention sur la désintégration H −→ W W ∗ . Les événements avec de faux (non-prompt) leptons représentent le bruit de fond dominant, mais réductible, de l’état final considéré. L’estimation de ce bruit de fond conditionne largement la sensibilité de l’analyse. Une méthode améliorant cette estimation a été développée et est discutée en détails dans ce rapport. Dominant l’erreur totale de la mesure, ce bruit de fond instrumental est mesuré de 1.5 à 3.6 fois supérieur à la prédiction des simulations et représente entre 32 et 48% du bruit de fond total. Le meilleur ajustement du rapport entre nombre d’événements observés et prédits par les valeurs de section efficace du Modèle Standard pour la production t t ̄ H, mesuré conjointement avec les autres canaux multi-leptoniques, est de 2.5 ± 0.7 (stat) +1.1 −0.9 (syst), avec une limite supérieure observéede 4.9 (2.3 attendue) à 95% de niveau de confiance
Low-Mass Diphoton Resonances Search With the ATLAS Detector at 13 TeV
No full textSeveral models beyond the standard model (BSM) predict new resonances decaying into two photons. The diphoton final state has the advantage of a clean experimental signature with an excellent mass resolution and moderate background. Using this final state, the CMS Collaboration observed a small excess near 95 GeV with a local (global) significance of 2.8 (1.3) standard deviations when combining data recorded at 8 TeV and 13 TeV. A search for a narrow diphoton resonance X of mass mX is also performed by ATLAS experiment in the low-mass range 65 to 110 GeV, below the SM Higgs boson mass of 125 GeV, using 80 fb−1 of pp collision data recorded at 13 TeV at the Large Hadron Collider. In this range, in addition to the smoothly falling continuum background composed of photon pairs (γγ), as well as photon–jet (γj) and jet pairs (jj) with mis-identified jets, a Drell-Yan (DY) component is present. The events are split into three categories depending on how the two photon candidates are reconstructed. A model composed of analytic functions that describe the signal and background (including γγ, γj, jj and DY) is fit to the measured diphoton mass spectrum to search for narrow resonances. The dominant uncertainties arise from the uncertainty due to the choice of analytic functions to model the continuum background. No significant excess with respect to the Standard Model expectation is found in ATLAS experiment, and a limit at the 95% confidence level is set on narrow resonance fiducial cross-section times branching ratio ranging from 30 to 101 fb
Performance of the ATLAS RPC Detector and L1 Muon Barrel Trigger at 13 TeV
No full textThe ATLAS experiment at the Large Hadron Collider utilises a trigger system consisting of a first level hardware trigger and a higher level software trigger. The Level-1 muon trigger system selects muon candidates with six transverse momentum thresholds and associate them with a correct LHC bunch crossing. The Level-1 Muon Barrel Trigger uses Resistive Plate Chambers (RPC) detectors to generate trigger signals for selecting muon candidates within the pseudorapidity range of up to 1.05. The RPC detectors are arranged in three concentric double layers and consist of 3600 gas volumes, with a total surface of more than 4000 square meters, that operate in a toroidal magnetic field. This contribution will discuss performance of the RPC detector system and of the Level-1 Muon Barrel trigger during the 2018 data taking period. Measurements of RPC detector response obtained using muon candidates produced in LHC collisions will be presented. Trigger performance and efficiency measurements that are obtained using Z boson decays to a muon pair will be also discussed. Finally, studies of the RPC detector response at different high voltage and threshold settings will be discussed, in the context of expected detector response after the High Luminosity LHC upgrades
Testing the Standard Model in boosted top quark production with the ATLAS experiment at the LHC
No full textMeasurements in boosted top quark production test the Standard Model in a previously unexplored regime with a strongly enhanced sensitivity to high-scale new phenomena. Dedicated techniques have been developed to reconstruct and identify boosted top quarks. In this contribution, several new measurements of the ATLAS experiment are presented of the differential cross section and asymmetries in this extreme kinematic regime. The measurements are interpreted within the Standard Model Effective Field Theory, yielding stringent bounds on the Wilson coefficients of two-light-quark-two-quark operators
Searching for additional Higgs bosons at ATLAS
No full textThe discovery of the Higgs boson with the mass of about 125 GeV completed the particle content predicted by the Standard Model. Even though this model is well established and consistent with many measurements, it is not capable to solely explain some observations. Many extensions of the Standard Model addressing such shortcomings introduce additional Higgs-like bosons which can be either neutral or charged. The current status of searches for additional low- and high-mass Higgs bosons based on the full LHC Run 2 dataset of the ATLAS experiment at 13 TeV are presented
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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