Search For New Phenomena In Top Antitop Quarks Final States With Additional Heavy Flavour Jets With The Atlas Detector
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Search For New Phenomena In Top Antitop Quarks Final States With Additional Heavy Flavour Jets With The Atlas Detector
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Author : Daiki Yamaguchi
language : en
Publisher: Springer Nature
Release Date : 2019-10-30
Search For New Phenomena In Top Antitop Quarks Final States With Additional Heavy Flavour Jets With The Atlas Detector written by Daiki Yamaguchi and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019-10-30 with Science categories.
This book reports on the search for a new heavy particle, the Vector-Like Top quark (VLT), in the Large Hadron Collider (LHC) at CERN. The signal process is the pair production of VLT decaying into a Higgs boson and top quark (TT→Ht+X, X=Ht, Wb, Zt). The signal events result in top–antitop quarks final states with additional heavy flavour jets. The book summarises the analysis of the data collected with the ATLAS detector in 2015 and 2016. In order to better differentiate between signals and backgrounds, exclusive taggers of top quark and Higgs boson were developed and optimised for VLT signals. These efforts improved the sensitivity by roughly 30%, compared to the previous analysis. The analysis outcomes yield the strongest constraints on parameter space in various BSM theoretical models. In addition, the book addresses detector operation and the evaluation of tracking performance. These efforts are essential to properly collecting dense events and improving the accuracy of the reconstructed objects that are used for particle identification. As such, they represent a valuable contribution to data analysis in extremely dense environments.
Search For New Physics In Tt Final States With Additional Heavy Flavor Jets With The Atlas Detector
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Author : Javier Montejo Berlingen
language : en
Publisher: Springer
Release Date : 2016-07-20
Search For New Physics In Tt Final States With Additional Heavy Flavor Jets With The Atlas Detector written by Javier Montejo Berlingen and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016-07-20 with Science categories.
This doctoral thesis focuses on the search for new phenomena in top-antitop quark (tt) final states with additional b-quark jets at the LHC. It uses the full Run 1 dataset collected by the ATLAS experiment in proton-proton collisions at √s=8 TeV. The final state of interest consists of an isolated lepton, a neutrino and at least six jets with at least four b-tagged jets, a challenging experimental signature owing to the large background from tt+heavy-flavor production. This final state is characteristic of ttH production, with the Higgs boson decaying into bb, a process that allows direct probing of the top-Higgs Yukawa coupling. This signature is also present in many extensions of the Standard Model that have been proposed as solutions to the hierarchy problem, such as supersymmetry or composite Higgs models, which predict the pair production of bosonic or fermionic top quark partners, or the anomalous production of four-top-quark events. All these physics processes have been searched for using an ambitious search strategy that has been developed on the basis of a combination of state-of-art theoretical predictions and a sophisticated statistical analysis to constrain in-situ the large background uncertainties. As a result, the most restrictive bounds to date on the above physics processes have been obtained.
Search For New Phenomena With Top Quark Pairs In Final States With One Lepton Jets And Missing Transverse Momentum In Pp Collisions At Square Root S
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Author : ATLAS Collaboration CERN
language : en
Publisher:
Release Date : 2021
Search For New Phenomena With Top Quark Pairs In Final States With One Lepton Jets And Missing Transverse Momentum In Pp Collisions At Square Root S written by ATLAS Collaboration CERN and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021 with categories.
Abstract: A search for new phenomena with top quark pairs in final states with one isolated electron or muon, multiple jets, and large missing transverse momentum is performed. Signal regions are designed to search for two-, three-, and four-body decays of the directly pair-produced supersymmetric partner of the top quark (stop). Additional signal regions are designed specifically to search for spin-0 mediators that are produced in association with a pair of top quarks and decay into a pair of dark-matter particles. The search is performed using the Large Hadron Collider proton-proton collision dataset at a centre-of-mass energy of s√ = 13 TeV recorded by the ATLAS detector from 2015 to 2018, corresponding to an integrated luminosity of 139 fb−1. No significant excess above the Standard Model background is observed, and limits at 95% confidence level are set in the stop-neutralino mass plane and as a function of the mediator mass or the dark-matter particle mass. Stops are excluded up to 1200 GeV (710 GeV) in the two-body (three-body) decay scenario. In the four-body scenario stops up to 640 GeV are excluded for a stop-neutralino mass difference of 60 GeV. Scalar and pseudoscalar dark-matter mediators are excluded up to 200 GeV when the coupling strengths of the mediator to Standard Model and dark-matter particles are both equal to one and when the mass of the dark-matter particle is 1 GeV
Search For Flavor Changing Neutral Current Top Quark Decays T Hq With H Bb In Pp Collisions At S 8 Tev With The Atlas Detector
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Author : Shota Tsiskaridze
language : en
Publisher: Springer
Release Date : 2017-08-02
Search For Flavor Changing Neutral Current Top Quark Decays T Hq With H Bb In Pp Collisions At S 8 Tev With The Atlas Detector written by Shota Tsiskaridze and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017-08-02 with Science categories.
This PhD thesis focuses on the search for flavor-changing neutral currents in the decay of a top quark to an up-type quark (q = u, c) and the Standard Model Higgs boson, where the Higgs boson decays to bb. Further, the thesis presents the combination of this search for top quark pair events with other ATLAS searches – in the course of which the most restrictive bounds to date on tqH interactions were obtained. Following on from the discovery of the Higgs boson, it is particularly important to measure the Yukawa couplings of the Standard Model fermions; these parameters may provide crucial insights to help solve the flavor puzzle and may help reveal the presence of new physics before it is directly observed in experiments.
Top Antitop Energy Asymmetry In Jet Associated Top Quark Pair Production At Atlas
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Author : Alexander Basan
language : en
Publisher:
Release Date : 2022
Top Antitop Energy Asymmetry In Jet Associated Top Quark Pair Production At Atlas written by Alexander Basan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022 with categories.
The Standard Model (SM) of particle physics, representing our current understanding of fundamental particles and their interactions, gives correct predictions with an astonishing precision for tens of thousands of measurements. Remaining open questions, like the observed matter-antimatter asymmetry in our universe and observations hinting at the existence of dark matter point to new physics beyond the Standard Model. Observables in the top-quark sector are particularly well suited to probe the SM and many extensions thereof at the electroweak symmetry-breaking scale and beyond. At proton-proton colliders, top-antitop-quark pair production is symmetric at leading order in quantum chromodynamics under the exchange of the top and antitop quarks, while interferences at higher orders in quark-antiquark annihilation create an asymmetry. This charge asymmetry can provide sensitive probes for many models beyond the SM like massive colour-octet states, extra dimensions, flavour-violating gauge bosons or axigluons. In jet-associated top-quark pair production, this asymmetry arises already at leading order in quark-gluon interactions. Furthermore, the final states in jet-associated top-antitop events allow for the definition of a new observable, the energy asymmetry, reflecting the different probability of top and antitop quarks to have the higher energy. The ATLAS experiment at the Large Hadron Collider at CERN collected 139 fb^-1 of proton-proton collision data at a centre-of-mass energy of 13 TeV during Run 2 in the data-taking period 2015-2018, providing the possibility to study less frequent processes like jet-associated top-quark pair production as well as essentially all interactions of the top quark with high statistical precision. This thesis presents the first measurement of the energy asymmetry, performed in the semi-leptonic decay channel in jet-associated top-quark pair events in the so called boosted topology, requiring the hadronically decaying top quark to have a transverse momentum above 350 GeV, and corrected for detector effects with the Fully Bayesian Unfolding (FBU) method. The measured asymmetry is found to be in agreement with the SM prediction at next-to-leading order accuracy in all three bins of the jet-scattering angle. In the central region, where the energy asymmetry is expected to be the highest, the energy asymmetry is measured to be -0.043+-0.020, in agreement with the SM prediction of -0.037+- 0.003. The Standard Model Effective Field Theory (SMEFT) represents a model-independent framework for new physics interpretations. Within the SMEFT framework, the energy asymmetry is especially sensitive to the chiral and colour structure of four-quark operators. The sensitivity of the energy asymmetry is presented in the bounds on Wilson coefficients obtained from one and two-dimensional fits of the predicted to the measured asymmetry. The sensitivity of the energy asymmetry is found to be comparable to that of other observables in the top-quark sector as well as to resolve blind directions in current LHC fits and will thus provide a valuable new input for global SMEFT fits.
Search For New Physics With Top And Bottom Quarks With Atlas
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Author :
language : en
Publisher:
Release Date : 2013
Search For New Physics With Top And Bottom Quarks With Atlas written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.
The studies performed by the principal investigator during the period of the grant constitute the ground work for search for new physics in channels including top and bottom quarks with the ATLAS detector at the Large Hadron Collider. The PI has been involved in search for heavy charged Higgs bosons decaying into top and bottom quark pairs, and top quark rare decays involving Higgs bosons and c-quarks. Both channels have the top quark pair production as their main background, which was studied in detail. The search for heavy charged Higgs and top quark rare decays requires signi cant amount of data accumulated by the experiment. In case no signal is observed in the present data sample collected by ATLAS (5 fb−1 of integrated luminosity at proton-anti proton center-of-mass energy of 7 TeV and 20 fb−1 at 8 TeV), data from the upgraded detector running at 14 TeV needs to be analyzed. The PI has been working on physics and performance studies at upgraded detector.
Searches For Supersymmetric Particles In Final States With Multiple Top And Bottom Quarks With The Atlas Detector
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Author : Chiara Rizzi
language : en
Publisher:
Release Date : 2018
Searches For Supersymmetric Particles In Final States With Multiple Top And Bottom Quarks With The Atlas Detector written by Chiara Rizzi and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with categories.
En esta tesis se presentan dos búsquedas de Supersimetría en colisiones protón-protón en el Gran Colisionador de Hadrones (LHC, por sus siglas en inglés) del CERN, centradas en modelos que dan lugar a la producción de múltiples quarks top o quarks bottom en el estado final. La primera búsqueda tiene como objetivo la producción de pares de gluinos, donde cada gluino de desintegra a través de un squark top (modelo Gtt) o un squark bottom (modelo Gbb) en una pareja de quarks top-antitop o bottom-antibottom, respectivamente, y un neutralino, que es la partícula supersimétrica más ligera (LSP, por sus siglas en inglés). Cada quak top a su vez se desintegra en un bosón W y un quark bottom. Consecuentemente, el estado final se caracteriza por una alta multiplicidad de bottom jets (b-jets), que son chorros de partículas resultantes de la hadronización de quarks bottom, así como un alto momento transverso faltante (Emiss T ) debido a que la LSP escapa sin ser detectada. La segunda búsqueda tiene como objetivo la producción de pares de higgsinos en el contexto de un modelo GGM, en el cual cada higgsino se desintegra en el bosón de Higgs del Model Estándar y un gravitino, que en este caso juega el papel de la LSP. Esta búsqueda se centra en sucesos donde ambos bosones de Higgs se desintegran en parejas de quarks bottom-antibottom, de nuevo dado lugar a estados finales con múltiples b-jets. Este es el primer análisis en ATLAS optimizado para esta signatura, la cual había sido considerada previamente en búsquedas llevadas a cabo por la colaboración CMS. Ambas búsquedas en esta tesis usan los datos recopilados por el experimento ATLAS en el LHC entre el 2015 y el 2016, a una energía del centro de masas de ps = 13 TeV, correspondiente a una luminosidad integrada de 36.1 fb−1. La búsqueda de gluinos, sin optimización adicional, ha sido extendida usando los datos recopilados en el 2017, resultando en una luminosidad integrada total de 79.8 fb−1. No habiendo encontrado un exceso significativo de sucesos sobre la predicción del Modelo Estándar en ninguna de las regiones de búsqueda, los resultados han sido usados para establecer límites superiores a la producción de partículas supersimétricas. La primera búsqueda excluye a un nivel de confianza del 95% masas del gluino de hasta 2.25 TeV para el modelo Gtt y de hasta 2.17 TeV para el modelo Gbb, en ambos casos para masas del neutralino menores que 800 GeV. La segunda búsqueda excluye masas del higgsino en el rango de 240–880 GeV, asumiendo que el higgsino se descompone exclusivamente en un bosón de Higgs y un gravitino.
Search For Top Antitop Quark Resonances In The Lepton Jets Final State With The Cms Detector Preparing The Run 3 Analysis
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Author : Johanna Matthiesen
language : en
Publisher:
Release Date : 2023
Search For Top Antitop Quark Resonances In The Lepton Jets Final State With The Cms Detector Preparing The Run 3 Analysis written by Johanna Matthiesen and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2023 with categories.
Search For Heavy Down Type Vector Like Quarks In The Lepton Plus Jets Final State In 8 Tev Proton Proton Collisions Using The Atlas Detector At The Lhc
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Author : Diedi Hu
language : en
Publisher:
Release Date : 2015
Search For Heavy Down Type Vector Like Quarks In The Lepton Plus Jets Final State In 8 Tev Proton Proton Collisions Using The Atlas Detector At The Lhc written by Diedi Hu and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
In the chiral B scenario with a 100% branching ratio of the decay B->Wt, the observed (expected) 95% CL lower limit on the B mass is 814 GeV (756 GeV).
Search For A Heavy Top Like Quark In P Bar P Collisions At Surd S
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Author :
language : en
Publisher:
Release Date : 2011
Search For A Heavy Top Like Quark In P Bar P Collisions At Surd S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
We present the results of a search for pair production of a heavy top-like (t') quark decaying to W q final states using data corresponding to an integrated luminosity of 5.6 fb−1 collected by the CDF II detector in p{anti p} collisions at √{ovr s} = 1.96 TeV. We perform parallel searches for t' → W b and t' → W q (where q is a generic down-type quark) in events containing a lepton and four or more jets. By performing a fit to the two-dimensional distribution of total transverse energy versus reconstructed t' quark mass, we set upper limits on the t'{anti t}' production cross section and exclude a standard model fourth-generation t' quark decaying to W b (W q) with mass below 358 (340) GeV/c2 at 95% CL.