A search for Beyond the Standard Model physics is performed with the ATLAS detector in the opposite sign dimuon channel using the 20 fb 1 of data collected in 2012 at √s = 8 TeV. No excess is found above the Standard Model expectation. Using a Bayesian statistical analysis, model dependent 95% Credibility Level Bayesian exclusion limits are extracted for two models of gravitationally-related beyond the Standard Model phenomena. For the ADD and RS quantum black hole models, limits of 3.32 and 1.95 TeV are set on the extradimensional Planck Scale, and for ADD Large Extra dimensions, limits ranging from 2.8-4.4 TeV are set on the string scale for the GRW, HLZ and Hewett formalisms. In addition, a study is performed to estimate the effect of increasing noise cuts in the ATLAS Level-1 Calorimeter Trigger on the physics efficiency of W ! e and t¯t and on the Level-1 missing transverse energy trigger rate. Results suggest that higher noise cuts could reduce the Level-1 missing transverse energy trigger rate with a minimal loss of physics efficiency.

In 2012 a resonance with a mass of 125 GeV resembling the elusive Higgs boson was discovered simultaneously by the ATLAS and CMS experiments using data collected from the Large Hadron Collider (LHC) at CERN. Its observation finally confirms the mechanism for Spontaneous Electroweak Symmetry Breaking (EWSB) necessary for describing the mass structure of the electroweak (EW) gauge bosons. In 2013, Peter Higgs and Francois Englert were awarded the Nobel Prize in physics for their work in developing this theory of EWSB now referred to as the Higgs mechanism. The explanation for EWSB is often referred to as the last piece of the puzzle required to build a consistent theory of particle physics known as the Standard Model. But does that mean that there are no new surprises to be found? Many EW processes have yet to be measured and are just starting to become accessible with the data collected at the LHC. Indeed, this unexplored region of EW physics may provide clues to as yet unknown new physics processes at higher energy scales. Using the 2012 LHC data recorded by the ATLAS experiment, we seek to make the first observation of one such EW process, the massive tri-boson final state: WWW. It represents one of the first searches to probe the Standard Model WWWW coupling directly at a collider. This search looks specifically at the channel where each W boson decays to a charged lepton and a neutrino, offering the best sensitivity for making such a measurement. In addition to testing the Standard Model directly, we also use an effective field theory approach to test for the existence of anomalous quartic gauge couplings which could offer evidence for new physics at higher energies than those produced by the LHC.

A search for the Standard Model Higgs Boson decaying to two muons in proton-proton collisions with the Compact Muon Solenoid experiment is performed. Building on top of the success of previous CMS analyses (CMS Run I campaign), results are presented using 35.9 fb−1 of data collected over the course of 2016 (CMS Run II campaign) at a center-of-mass energy of √s = 13 TeV. During the Long Shutdown 1 of the Large Hadron Collider, the CMS detector underwent substantial hardware changes. The second topic discusses the process of calibration of the CMS Hadron Forward Calorimeter in preparation for collisions after LS1. The final chapter discusses the process of building simulations of calorimeter systems. Walking through all the steps from geometry specification to readout definition the results for two standalone calorimeters are presented that have been proposed as potential replacements for respective CMS components.

No description available.

Détection et identification de la réaction quark + anti-quark -> e+ + e- à l'aide du détecteur CMS (Compact Muon Solenoid) auprès du Grand Collisionneur de Hadrons du CERN, le LHC. Cette réaction permet de tester avec précision le Modèle Standard et de rechercher d'éventuelles nouvelles particules (Z') prédites par les théories de grande unification (GUT) et par les modèles à dimensions spatiales supplémentaires.

No description available.

Well motivated theoretical models predict the annihilation of dark matter (DM) into standard model particles, a phenomenon which could be a significant source of photons in the gamma-ray sky. With its unprecedented sensitivity and its broad energy range (20 MeV to more than 300 GeV) the main instrument on board the Fermi satellite, the Large Area Telescope (LAT), might be able to detect an indirect signature of DM annihilations. In this work we revisit several interesting claims of extended dark matter emission made from analyses of Fermi-LAT data: First, based on three years of Fermi Large Area Telescope (LAT) gamma-ray data of the Virgo cluster, evidence for an extended emission associated with dark matter pair annihilation in the bb̄ channel has been reported by Han et al. (arxiv:1201.1003). After an in depth spatial and temporal analysis, we argue that the tentative evidence for a gamma-ray excess from the Virgo cluster is mainly due to the appearance of a population of previously unresolved gamma-ray point sources in the region of interest. These point sources are not part of the LAT second source catalogue (2FGL), but are found to be above the standard detection significance threshold when three or more years of LAT data is included. Second, we confirm the detection of a spatially extended excess of 2-5 GeV gamma rays from the Galactic Center (GC), consistent with the emission expected from annihilating dark matter or an unresolved population of about 10³ milisecond pulsars. However, there are significant uncertainties in the diffuse galactic background at the GC. We have performed a revaluation of these two models for the extended gamma ray source at the GC by accounting for the systematic uncertainties of the Galactic diffuse emission model. We also marginalize over point source and diffuse background parameters in the region of interest. We show that the excess emission is significantly more extended than a point source. We find that the DM (or pulsars population) signal is larger than the systematic errors and therefore proceed to determine the sectors of parameter space that provide an acceptable fit to the data. We found that a population of order a 10³ MSPs with parameters consistent with the average spectral shape of Fermi-LAT measured MSPs was able to fit the GC excess emission. For DM, we found that a pure τ⁺τ⁻ annihilation channel is not a good fit to the data. But a mixture of τ⁻τ⁻ and bb̄ with a (σν) of order the thermal relic value and a DM mass of around 20 to 60 GeV provides an adequate fit. We also consider the possibility that the GeV excess is due to nonthermal bremsstrahlung produced by a population of electrons interacting with neutral gas in molecular clouds. The millisecond pulsars and dark matter alternatives have spatial templates well fitted by the square of a generalized Navarro-Frenk-White (NFW) profile with inner slope γ = 1.2. We model the third option with a 20-cm continuum emission Galactic Ridge template. A template based on the HESS residuals is shown to give similar results. The gamma-ray excess is found to be best fit by a combination of the generalized NFW squared template and a Galactic Ridge template. We also find the spectra of each template is not significantly affected in the combined fit and is consistent with previous single template fits. That is, the generalized NFW squared spectrum can be fit by either of order 10³ unresolved MSPs or DM with mass around 30 GeV, a thermal cross section, and mainly annihilating to bb̄ quarks. While the Galactic Ridge continues to have a spectrum consistent with a population of nonthermal electrons whose spectrum also provides a good fit to synchrotron emission measurements. We also show that the current DM fit may be hard to test, even with 10 years of Fermi-LAT data, especially if there is a mixture of DM and MSPs contributing to the signal, in which case the implied DM cross section will be suppressed.

This thesis outlines the prospects for top quark mass measurement through the Fully Hadronic decay of top-antitop events with the ATLAS detector. Methods with and without b-tagging were explored. Without b-tagging the signal was hidden beneath the QCD multi-jet background and prospects for a mass measurement do not appear to be good. A standard and a pessimistic b-tagging likelihood significance value were explored. The standard value gives a S/B of 0.88 and the more pessimistic value gives a S/B of 0.79. For 1 fb−1 a significance of 36.8 and 32.0 can be obtained for the standard and pessimistic scenarios respectively. A selection efficiency of 1.4% and 1.1% can be achieved for the standard and pessimistic values respectively. Assuming a top mass of 174 GeV, a mass peak can clearly be seen for both b-tagging values. For the standard scenario, a top mass of 168.94 GeV with a statistical error of 0.33 GeV can be extracted. With the pessimistic scenario, the extracted mass is 169.11 GeV with a statistical error of 0.36 GeV. This is the first attempt with fully simulated events and therefore there are possibilities for improvement. This analysis did not include b-jet energy scale correction.

Using a measure of the jet energy resolution that relies on momentum balance in direct photon events, a correction to the modelled detector resolution is developed. The correction is produced by iteratively unfolding the model from the measured data. Jets in the model are then smeared using this correction, and the result is compared to the data using a χ2 test. This method is shown to be effective at improving the agreement between the data and the model, even when the model initially shows poor agreement to the data. / Graduate / 0798 / bmoir@ualberta.net

First, we review the basics of baryogenesis and models for baryogenesis in the early literature. Then, we discuss the main theme in this thesis, electroweak baryogenesis, which utilizes the electroweak phase transition. We present how the phase transition can be used to achieve baryogenesis. Next, we develop our model, which is the Standard Model with a singlet field coupled to the Higgs doublet negatively and to the right-handed neutrinos. It is a simple extension of the singlet Majoron model. We focus on numerical analysis of the model. Parameter space satisfying all the conditions are found and relevant quantities, such as the critical temperature, the Higgs mass, and the mixing angle are found as well. It turns out that LEP bound on the Higgs mass and the mixing angle is a strong constraint, and only a small fraction of parameter space is acceptable for attaining a strong enough phase transition for baryogenesis.