Tests of the current understanding of physics at the highest energies achievable in man-made experiments are performed at CERN’s Large Hadron Collider. In the theory of the strong force within the Standard Model of particle physics - Quantum ChromoDynamics or QCD - confined quarks and gluons from the proton-proton scattering manifest themselves as groups of collimated particles. These particles are clustered into physically measurable objects called hadronic jets. As jets are widely produced at hadron colliders, they are the key physics objects for an early "rediscovery of QCD". This thesis presents the first jet measurement from the ATLAS Collaboration at the LHC and confronts the experimental challenges of precision measurements. Inclusive jet cross section data are then used to improve the knowledge of the momentum distribution of quarks and gluons within the proton and of the magnitude of the strong force.

This book describes research in two different areas of state-of-the-art hadron collider physics, both of which are of central importance in the field of particle physics. The first part of the book focuses on the search for supersymmetric particles called gluinos. The book subsequently presents a set of precision measurements of “multi-jet” collision events, which involve large numbers of newly created particles, and are among the dominant processes at the Large Hadron Collider (LHC). Now that a Higgs boson has been discovered at the LHC, the existence (or non-existence) of supersymmetric particles is of the utmost interest and significance, both theoretically and experimentally. In addition, multi-jet collision events are an important background process for a wide range of analyses, including searches for supersymmetry.

This book addresses one of the most intriguing mysteries of our universe: the nature of dark matter. The results presented here mark a significant and substantial contribution to the search for new physics, in particular for new particles that couple to dark matter. The first analysis presented is a search for heavy new particles that decay into pairs of hadronic jets (dijets). This pioneering analysis explores unprecedented dijet invariant masses, reaching nearly 7 TeV, and sets constraints on several important new physics models. The two subsequent analyses focus on the difficult low dijet mass region, down to 200 GeV, and employ a novel technique to efficiently gather low-mass dijet events. The results of these analyses transcend the long-standing constraints on dark matter mediator particles set by several existing experiments.

The Large Hadron Collider (LHC) is the highest energy collider ever built. It resides near Geneva in a tunnel 3.8m wide, with a circumference of 26.7km, which was excavated in 1983-1988 to initially house the electron-positron collider LEP. The LHC was approved in 1995, and it took until 2010 for reliable operation. By now, a larger set of larger integrated luminosities have been accumulated for physics analyses in the four collider experiments: ATLAS, CMS, LHCb and ALICE.The LHC operates with an extended cryogenic plant, using a multi-stage injection system comprising the PS and SPS accelerators (still in use for particle physics experiments at lower energies). The beams are guided by 1232 superconducting high field dipole magnets.Intense works are underway in preparation of the High Luminosity LHC, aimed at upgrading the LHC and detectors for collecting ten times more luminosity, and extending the collider life to the early 2040's. So far, the (HL-)LHC project represents a cumulation of around one hundred thousand person-years of innovative work by technicians, engineers, and physicists from all over the world; probably the largest scientific effort ever in the history of humanity. The book is driven by the realisation of the unique value of this accelerator complex and by the recognition of the status of high energy physics, described by a Standard Model — which still leaves too many questions unanswered to be the appropriate theory of elementary particles and their interactions.Following the Introduction are: three chapters which focus on the initial decade of operation, leading to the celebrated discovery of the Higgs Boson, on the techniques and physics of the luminosity upgrade, and finally on major options - of using the LHC in a concurrent, power economic, electron-hadron scattering mode, when upgraded to higher energies or eventually as an injector for the next big machine. The various technical and physics chapters, provided by 61 authors, characterise the fascinating opportunities the LHC offers for the next two decades ahead (possibly longer), with the goal to substantially advance our understanding of nature.

The first part of this thesis presents the measurement of the inclusive cross-section for electron production from heavy-flavour decays in the electron transverse momentum range 7 GeV

This text gives an introduction to particle physics at a level accessible to advanced undergraduate students. It is based on lectures given to 4th year physics students over a number of years, and reflects the feedback from the students. The aim is to explain the theoretical and experimental basis of the Standard Model (SM) of Particle Physics with the simplest mathematical treatment possible. All the experimental discoveries that led to the understanding of the SM relied on particle detectors and most of them required advanced particle accelerators. A unique feature of this book is that it gives a serious introduction to the fundamental accelerator and detector physics, which is currently only available in advanced graduate textbooks. The mathematical tools that are required such as group theory are covered in one chapter. A modern treatment of the Dirac equation is given in which the free particle Dirac equation is seen as being equivalent to the Lorentz transformation. The idea of generating the SM interactions from fundamental gauge symmetries is explained. The core of the book covers the SM. The tools developed are used to explain its theoretical basis and a clear discussion is given of the critical experimental evidence which underpins it. A thorough account is given of quark flavour and neutrino oscillations based on published experimental results, including some from running experiments. A simple introduction to the Higgs sector of the SM is given. This explains the key idea of how spontaneous symmetry breaking can generate particle masses without violating the underlying gauge symmetry. A key feature of this book is that it gives an accessible explanation of the discovery of the Higgs boson, including the advanced statistical techniques required. The final chapter gives an introduction to LHC physics beyond the standard model and the techniques used in searches for new physics. There is an outline of the shortcomings of the SM and a discussion of possible solutions and future experiments to resolve these outstanding questions. For updates, new results, useful links as well as corrections to errata in this book, please see the book website maintained by the authors: https://pplhcera.physics.ox.ac.uk/