This thesis focuses on searches for squarks with the ATLAS detector in "compressed" scenarios where the scalar top is very close in mass to the lightest supersymmetric particle. These models are theoretically appealing because the presence of a quasi-degenerate scalar top enhances the self-annihilation cross-section of the lightest supersymmetric particle, acting therefore as a regulator of the dark matter relic density. Two main analyses are presented: the first is a search for scalar tops decaying to charm quarks. The identification of jets originating from the charm quark is very challenging due to its short lifetime. The calibration of tools for charm-tagging has paved the way to measuring the decay of the Higgs boson to pairs of charm quarks. The second analysis presented is the development of a novel technique for reconstructing low momentum b-hadrons. This tool has enabled the ATLAS collaboration to explore topologies that were previously inaccessible.

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.

Supersymmetry (SUSY) is a new symmetry that relates bosons and fermions, which has strong support at both the mathematical and the physical level. This book offers a comprehensive review, following the development of SUSY from its very early days up to present. The order of the contributions should provide the reader with the historical development as well as the latest theoretical updates and interpretations, and experimental constraints from particle accelerators and dark matter searches. It is a great pleasure to bring together here contributions from authors who initiated or have contributed significantly to the development of this theory over so many years. To present a balanced point of view, the book also includes a closing contribution that attempts to describe the physics beyond the Standard Model in the absence of SUSY. The contributions to this book have been previously published in The European Physical Journal C - Particles and Fields.

What is the dark matter that fills the Universe and binds together galaxies? How was it produced? What are its interactions and particle properties?The paradigm of dark matter is one of the key developments at the interface of cosmology and elementary particle physics. It is also one of the foundations of the standard cosmological model. This book presents the state of the art in building and testing particle models for dark matter. Each chapter gives an analysis of questions, research directions, and methods within the field. More than 200 problems are included to challenge and stimulate the reader's knowledge and provide guidance in the practical implementation of the numerous 'tools of the trade' presented. Appendices summarize the basics of cosmology and particle physics needed for any quantitative understanding of particle models for dark matter.This interdisciplinary textbook is essential reading for anyone interested in the microscopic nature of dark matter as it manifests itself in particle physics experiments, cosmological observations, and high-energy astrophysical phenomena: from graduate students and advanced undergraduates to cosmologists and astrophysicists interested in particle models for dark matter and particle physicists interested in early-universe cosmology and high-energy astrophysics.

This volume is a compilation of the lectures at TASI 2012, held in Boulder, Colorado, June 2012. The program comprises two parallel lecture series on particle physics and on cosmology. The particle physics lectures covers LHC related experimental techniques, phenomenology, as well as basics in physics beyond the standard model. The cosmology series give a general introduction to modern cosmology with special attention to the topics of dark matter, the microwave background and alternatives to the standard model of cosmology. The lectures are accessible to graduate students at the initial stages of their research careers.

The traditional purpose of the Adriatic Meeting is to present most advanced scienti?c research conducted by the lecturers who take part in the development of their ?elds and, in addition, to provide a school-like atmosphere for young scientists. Dubrovnik, as a geographical centre of this region of Europe, provided a most adequate location for this conference. Having very agreeable surroundings, the conference site nevertheless gave a focus for very strong scienti?c interaction. The subjects chosen for the 8th meeting, in September 2001, were gauge theories, particle phenomenology, string theories and cosmology. We were able to bring together a very good cross section of outstanding scientists who gave extraorinarily good presentations. Certainely one reason for this success is that most of us feel obliged to help the scienti?c life in South East Europe return to its former level. However, there are very exciting new scienti?c developments as well. Part of the meeting was dominated by neutrino physics which has just seen exciting progress by establishing neutrino masses experimentally. This was d- cussed within neutrino masses and grand uni?ed theories (GUTs). General - pects of neutrino physics and CP violation, neutrino mixing and the bayron asymmetry were presented along the same lines. On the theoretical side the idea of the construction of gauge theories on non-commutative spaces and their phenomenological implications is accepted worldwide within the particle physics community.

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.

This proceedings volume contains pedagogical lectures on theoretical and experimental particle physics, cosmology and atomic trap physics. It also includes additional contributions that provide up-to-date information on new experimental results from accelerators, underground laboratories, and nuclear astrophysics. This combination of pedagogical talks and topical short talks provides comprehensive information to researchers in the fields of particle physics, cosmology and atomic trap physics. Sample Chapter(s). Chapter 1: New Physics in B and K Decays (1,704 KB). Contents: Cosmic Ray Velocity and Electric Charge Measurements in the AMS Experiment (L Arruda); Flavor and Chiral Oscillations with Dirac Spinors (A E Bernardini); Modification of the Casimir Effect Due to a Minimal Length Scale (U Harbach); Parton Energy Loss, Saturation, and Recombination at BRAHMS (E-J Kim); Spatial Confinement and Thermal Deconfinement in the Compactified Gross-Neveu Model (J M C Malbouisson); Currents on Superconducting Strings in an Unusual Environment (M A Metlitski); QCD Results at CDF (O Norniella); Quantization of Galilean Covariant Fields (E S Santos); Physics of Heavy Flavour at CDF (S Torre); Resonance Production at STAR (H Zhang); and other papers. Readership: Graduate students, researchers and academics in high energy physics, particle physics and astrophysics.

The proceedings of DIS 2001 present the most updated status of deep inelastic scattering (DIS) physics. Topics like structure function measurements and phenomenology, QCD studies in DIS and photoproduction, spin physics and diffractive interactions are reviewed in detail, with emphasis on those studies that push the test of QCD and the Standard Model to the limits of their present range of validity, towards both the very high and the very low four-momentum transfers in the lepton-proton scattering. Moreover, this workshop coincided with the transition between the first period of experimentation at the HERA ep collider at DESY and the start of the updated HERA II operation — allowing a review of what has been learned up to now and a discussion on the main future directions of research in this field.