Global ETD Search

1	Signatures of Dark Matter at the LHC : A phenomenological study combining collider and cosmological bounds to constrain a vector dark matter particle model Olsson, Anton January 2022 (has links) Everything that humans have ever touched, created or built something from consists of a type of matter that only makes up 15 percent of the total matter in the universe. The remaining 85 percent is attributed to dark matter, a so far not discovered and non-luminous type of matter. In this thesis a potential dark matter particle candidate has been studied by investigating an extension of the SU(2) symmetry into a dark gauge sector, where the new sector is connected to the standard model through a vector-like fermion portal. In order to understand how such an extension is made, the Lagrangian density of the standard model and its different gauge sectors were derived. The cross sections of the process of pair production of dark matter particles and tau leptons in the final state due to proton-proton collisions at the LHC was simulated with the software \texttt{MadGraph}. The cross sections were used to draw significance contours for the exclusion and discovery regions for parts of the parameter space of the new model, for current and projected luminosities of the LHC. The projected luminosity scans also consider how lowering the uncertainty in the number of background events through hypothetical improvements to detectors would impact the exclusion and discovery contours. The significance contours were combined with relic density constraints, derived from comparisons between measurements of the Planck telescope and calculations from the software \texttt{MicrOMEGAs}. The resulting graphs show that there are non-forbidden regions of the parameter space that are significant for exclusion and discovery for luminosity of current searches. Increasing the luminosity while keeping the uncertainty in the number of background events the same yielded only minor increases to the exclusion and discovery contours. Combining the projected luminosities with improvements to the background uncertainty instead produced exclusion and discovery regions that were significantly larger than those for the current luminosity. Dark matter particle phenomenology LHC MadGraph standard model beyond standard model Subatomic Physics Subatomär fysik
2	Simulation of Higgs boson pair production in Vector Boson Fusion at the LHC Romero, Daniela January 2021 (has links) MadGraph5 is used to generate events with Higgs boson pairs from vector boson fusion (VBF) at leading-order (LO) and next-to-leading-order (NLO) accuracy in QCD. The simulations are used to compute fiducial cross-sections in proton-proton collisions at a centre-of-mass energy of 13 TeV, using several kinematic cuts on the outgoing jets, e.g. the jet transverse momenta and pseudorapidity. The resulting cross-sections for NLO and LO are compared and their ratio, the K-factor, is calculated for every kinematic cut. An attempt is made to extend the NLO simulation for non-Standard Model (SM) couplings between two vector bosons and two Higgs bosons (VVHH), however the corresponding model was found to be only compatible with LO accuracy in QCD. Higgs boson vbf vector boson fusion high energy physics lhc proton collision madgraph simulation Subatomic Physics Subatomär fysik
3	Exotic Decays of a Vector-liketop Partner at the LHC Skwarcan-Bidakowski, Alexander January 2019 (has links) An evaluation of how sensitive some ATLAS searches for new physics are to a new beyond standard model (BSM) vector-like quark (VLQ) and a pseudo Nambu-Goldstone boson (pNGB) scalar. This was done by simulating a signal containing these new particles and making a recast of it onto existing verified ATLAS searches for new physics at center-of-mass (CM) energy of 13 TeV (Run 2) at the Large Hadron Collider (LHC). Signals for recasting were tailored such that their final states would be appropriate in relation to each respective ATLAS search in order to use the same selection criteria as applied in the existing searches. The results are summarized in the form of significances (Z) for each masspoint of the new top-partner and S particle. Significances did not show any expectiation of excluding any masspoint in the examined mass range for the recasts at 95% CL. This suggests that a dedicated search for these particles in the considered masspoints would be required. Particle physics Vector-like quarks VLQ Composite Higgs model CHM Top-partner pseudo Nambu-Goldstone boson pNGB NGB ATLAS LHC CMS Significance Recast CheckMate CM MadGraph Pythia Delphes Detector Analysis Hierarchy Problem Exotic Decay QFT Quantum Field Theory fermions bosons Jets photons leptons 13 TeV Missing Transverse Energy momentum hypothetical selection criteria Standard model Signal background event Higgs Mechanism Simulation Confidence limit Other Physics Topics Annan fysik Accelerator Physics and Instrumentation Acceleratorfysik och instrumentering Subatomic Physics Subatomär fysik

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