A search for the single production of vector-like quarks decaying to a W-boson and a b-quark in the leptonic final state with the ATLAS detector.

In dieser Dissertation wird eine Suche nach vektorartigen Quarks (VLQs) beim Zerfall in ein W-Boson und ein b-Quark vorgestellt. Die Suche wird mit Proton-Proton-Kollisionsdaten durchgeführt, die vom ATLAS-Detektor am CERN bei einer Schwerpunktsenergie von √s = 13 TeV zwischen 2015 und 2018 während dem LHC Run II gesammelt wurden. Die Existenz von VLQs wird von mehreren Theorien jenseits des Standardmodells postuliert, zudem sind VLQs ein einfaches Beispiel für Fermionen mit Farbladung, die immer noch mit experimentellen Beobachtungen konsistent sind. Diese Arbeit konzentriert sich auf den Fall, dass ein einzelnes VLQ erzeugt wird und in ein b-Quark und ein W-Boson zerfällt, das dann wiederum in ein geladenes Lepton und ein Neutrino zerfällt. Diese Suche schließt sich an mehrere Suchen nach einzeln und paarweise erzeugten VLQs am LHC an, die sowohl bei ATLAS als auch bei CMS durchgeführt wurden und deren Existenz bis zu einer Masse von über 1 TeV ausgeschlossen haben. Bei einer Masse von etwa 1.8 TeV wird ein Überschuss von 3.7 σ gegenüber der Vorhersage des Standardmodells beobachtet. Einige mögliche Masse/Kopplungskombinationen werden durch diese Analyse ausgeschlossen. Dies ist jedoch weniger Parameterraum als aufgrund eines unerwarteten Überschusses an beobachteten Ereignissen erwartet wurde.In this thesis, a search for vector-like quarks (VLQs) decaying into a W-boson and a b-quark is presented. The search is performed on proton-proton collision data collected by the ATLAS detector at CERN at a center-of-mass energy of √s = 13 TeV between 2015 and 2018, during Run II of the LHC. The existence of VLQs is consistent with several Beyond the Standard Model theories and VLQs are a simple example of coloured fermions that are still consistent with experimental observations. This work focuses on the case where a single VLQ is produced and decays to a b- quark and a W-boson, which then decays to a charged lepton and a neutrino. This search follows on several searches for singly- and pair-produced VLQs at the LHC from both ATLAS and CMS, which have excluded their existence up to over 1 TeV, and this search considers VLQs in a mass range from 1 TeV to 2.7 TeV. An excess over the Standard Model (SM) prediction of 3.7 σ is observed at a mass of around 1.8 TeV. Some possible mass/coupling combinations are excluded by this analysis. However, this is less parameter space than was expected due to an unexpected excess of observed events

Measurement of exclusive Di-Muon production in the ATLAS experiment

In this thesis a method for identifying exclusively produced di-muon pairs in proton-protoncollisions at the ATLAS experiment is described

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

The ten commandments in the nineteenth century /

Mode of access: Internet

The ten commandments in the nineteenth century /

Mode of access: Internet

Operation and performance of the ATLAS semiconductor tracker in LHC Run 2

Abstract The semiconductor tracker (SCT) is one of the tracking systems for charged particles in the ATLAS detector. It consists of 4088 silicon strip sensor modules. During Run 2 (2015–2018) the Large Hadron Collider delivered an integrated luminosity of 156 fb-1 to the ATLAS experiment at a centre-of-mass proton-proton collision energy of 13 TeV. The instantaneous luminosity and pile-up conditions were far in excess of those assumed in the original design of the SCT detector. Due to improvements to the data acquisition system, the SCT operated stably throughout Run 2. It was available for 99.9% of the integrated luminosity and achieved a data-quality efficiency of 99.85%. Detailed studies have been made of the leakage current in SCT modules and the evolution of the full depletion voltage, which are used to study the impact of radiation damage to the modules.</jats:p