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Author: Jan Küchler
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Category : Jets
Languages : en
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Author: Jan Küchler
Publisher:
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Category : Jets
Languages : en
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Author: Nicolas Maximilian Köhler
Publisher: Springer Nature
ISBN: 3030259889
Category : Science
Languages : en
Pages : 263
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Astrophysical observations implying the existence of Dark Matter and Dark Energy, which are not described by the Standard Model (SM) of particle physics, have led to extensions of the SM predicting new particles that could be directly produced at the Large Hadron Collider (LHC) at CERN. Based on 2015 and 2016 ATLAS proton-proton collision data, this thesis presents searches for the supersymmetric partner of the top quark, for Dark Matter, and for DarkEnergy, in signatures with jets and missing transverse energy. Muon detection is key to some of the most important LHC physics results, including the discovery of the Higgs boson and the measurement of its properties. The efficiency with which muons can be detected with the ATLAS detector is measured using Z boson decays. The performance of high-precision Monitored Drift Tube muon chambers under background rates similar to the ones expected for the High Luminosity-LHC is studied.
Author: Francesca Consiglia Ungaro
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Category :
Languages : en
Pages :
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Zusammenfassung: The elementary particles composing matter and their interactions are described by the Standard Model of particle physics. The Standard Model of particle physics enabled predictions that were experimentally verified and has been confirmed throughout the past decades by data. Nevertheless, there are several theoretical reasons not to consider it as the ultimate theory.The strongest motivation to expect Physics beyond the Standard Model is the hierarchy problem. The radiative corrections to the mass of the Higgs boson grow quadratically with the square of the energy scale at which the Standard Model is considered to be valid. As a result, the parameters of the Standard Model need to be fine-tuned in order for the mass of the Higgs boson to acquire the value experimentally measured, despite the possibly large corrections.Supersymmetry is a promising theory extending the Standard Model which solves many of its shortcomings, including the hierarchy problem. Supersymmetry postulates a new fermion-boson symmetry resulting in the introduction of new particles, called superpartners, with the same quantum numbers and masses as the Standard Model particles, except for the spin, differing by half a unit. This new symmetry enables a cancellation of the radiative corrections due to the Standard Model particles with the corrections due to the newly introduced superpartners, contributing with opposite sign. Since no superpartners with the same mass as the Standard Model particles have been observed, Supersymmetry must be broken to allow the superpartners to have a mass different from the mass of the corresponding Standard Model particles.In the minimal version of Supersymmetry in terms of new particles, the Minimal Supersymmetric Standard Model, the hierarchy problem can still be solved with a moderate amount of fine-tuning if the masses of at least some of the superpartners are at the TeV energy scale. The conservation of a new multiplicative quantum number, the R-parity, can be assumed to prevent phenomena in contrast with experimental evidences, as the proton decay. Superpartners have R-parity -1, and Standard Model particles R-parity +1. If the conservation of R-parity is assumed, in collider experiments supersymmetric particles can only be produced in even numbers (usually two), and the lightest supersymmetric particles (LSP, usually taken to be the neutralino), is stable.The LHC (Large Hadron Collider), is a hadron collider able to accelerate protons to unprecedented energies. Between 2010 and 2012 it operated at a centre-of-mass energy of the proton-proton collisions of 7 and 8 TeV.Its general-purpose experiments, ATLAS (A Toroidal LHC Apparatus) and CMS (Compact Muon Spectrometer) collected data corresponding to about 5 $fb^{-1}$ at $\sqrt{s}$ = 7 TeV and 20 $fb^{-1}$ at $\sqrt{s}$ = 8 TeV. The LHC and its experiments have been built with the main motivations of searching for the Higgs boson, discovered by the ATLAS and CMS experiments in 2012, and searching for signals of Supersymmetry.There are strong theoretical reasons to expect the supersymmetric particles to lie at the TeV energy scale, which would make them accessible at the LHC.In the Minimal Supersymmetric Standard Model, the lightest superpartner of the top quark, light stop is very likely to be lighter than the superpartners of the other quarks. This thesis focuses on the search for direct stop pair production with the data collected by the ATLAS experiment. Two analyses have been performed, addressing different final states and decay modes.The first analysis targets stop masses close to the mass of the top quark, ideal to solve the hierarchy problem.The mass spectrum assumed is such that m(stop)
Author: Maria Elena Stramaglia
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Category :
Languages : en
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Author: Jens Roggel
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Category :
Languages : en
Pages : 0
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Author: Marc Christopher Thomas
Publisher: Springer
ISBN: 3319434527
Category : Science
Languages : en
Pages : 113
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This thesis studies collider phenomenology of physics beyond the Standard Model at the Large Hadron Collider (LHC). It also explores in detail advanced topics related to Higgs boson and supersymmetry – one of the most exciting and well-motivated streams in particle physics. In particular, it finds a very large enhancement of multiple Higgs boson production in vector-boson scattering when Higgs couplings to gauge bosons differ from those predicted by the Standard Model. The thesis demonstrates that due to the loss of unitarity, the very large enhancement for triple Higgs boson production takes place. This is a truly novel finding. The thesis also studies the effects of supersymmetric partners of top and bottom quarks on the Higgs production and decay at the LHC, pointing for the first time to non-universal alterations for two main production processes of the Higgs boson at the LHC–vector boson fusion and gluon–gluon fusion. Continuing the exploration of Higgs boson and supersymmetry at the LHC, the thesis extends existing experimental analysis and shows that for a single decay channel the mass of the top quark superpartner below 175 GeV can be completely excluded, which in turn excludes electroweak baryogenesis in the Minimal Supersymmetric Model. This is a major new finding for the HEP community. This thesis is very clearly written and the introduction and conclusions are accessible to a wide spectrum of readers.
Author: Matthew Anthony
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Category :
Languages : en
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Author: Daiki Yamaguchi
Publisher: Springer Nature
ISBN: 9811509328
Category : Science
Languages : en
Pages : 279
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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.
Author: Javier Montejo Berlingen
Publisher: Springer
ISBN: 3319410512
Category : Science
Languages : en
Pages : 288
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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.
Author: Takuya Nobe
Publisher: Springer
ISBN: 9811000034
Category : Science
Languages : en
Pages : 229
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This book reports a search for theoretically natural supersymmetry (SUSY) at the Large Hadron Collider (LHC). The data collected with the ATLAS detector in 2012 corresponding to 20 /fb of an integrated luminosity have been analyzed for stop pair production in proton–proton collisions at a center-of-mass energy of 8 TeV at the Large Hadron Collider (LHC) in the scenario of the higgsino-like neutralino. The author focuses on stop decaying into a bottom quark and chargino. In the scenario of the higgsino-like neutralino, the mass difference between charginos and neutralinos (Δm) is expected to be small, and observable final-state particles are likely to have low-momentum (soft). The author develops a dedicated analysis with a soft lepton as a probe of particles from chargino decay, which suppresses the large amount of backgrounds. As a result of the analysis, no significant SUSY signal is observed. The 95% confidence-level exclusion limits are set to masses of stop and neutralino assuming Δm = 20 GeV. The region with ΔM (the mass difference between stop and neutralino) 70 GeV is excluded for the first time at stop mass of less than 210 GeV. The author also excludes the signals with ΔM 120 GeV up to 600 GeV of stop mass with neutralino mass of less than 280 GeV. The author clearly shows very few remaining parameter spaces for light stop (e.g., topology of stop decay is extremely similar to the SM top quark) by combining his results and previous ATLAS analyses. His results provide a strong constraint to searches for new physics in the future.
