Multiparton Interaction Models and Parton Shower Studies

University dissertation from Department of Astronomy and Theoretical Physics, Lund University

Abstract: Popular Abstract in English Experiments, such as the Large Hadron Collider (LHC) in CERN, Switzerland, collide particles together at high energies, in the hope of probing the fundamental constituents and forces of nature. On the theoretical side, the Standard Model (SM) is currently the best description we have. It is a theory that encompasses the strong, weak and electromagnetic forces, although excludes gravity. This thesis deals with topics related to Monte Carlo event generators; tools which, based on the theory, simulate these particle collisions, and give us an idea of what to expect at particle physics experiments. When protons are made to collide, as at the LHC, much of the physics will be dominated by the strong force. The part of the SM that describes this is known as Quantum Chromo Dynamics (QCD). It is not currently possible to solve this theory exactly, and many approximate methods are used. This thesis, in part, relates to parton showers, which describe the phenomenon that quarks and gluons (collectively known as partons, and the constituents of hadrons, such as the proton), can radiate other quarks and gluons, and in fact do so copiously under certain conditions. The other part of this thesis deals with multiparton interaction (MPI) models. MPI is a consequence of the composite nature of hadrons. For example, a proton is made up from three quarks, and will also contain many gluons which in turn can split into further quark-antiquark pairs. When two protons collide, it is hoped that one parton from each will interact together, but it is also possible for more than one pair to do so. These MPI affect the results from collider experiments, and so it is vital to have good models for them, such that their effect can be understood and disentangled from the data.