Derivation of Improved K^0_L Response Uncertainty for use in the Jet Energy Scale Calibration at ATLAS

Sammanfattning: The Standard Model of particle physics (SM) attempts to describe the fundamental particles and how they interact with each other. This model is however incomplete, as shown by various experimental observations. ATLAS is one of the experiments currently in operation at the Large Hadron Collider, which aims to search for new physics beyond the SM. To perform these searches, many ATLAS analyses look at collimated sprays of particles, called jets, coming from proton-proton collisions. The calibration of these jets is a multi-step process that uses both simulation and data-driven methods to derive different corrections. Some of these corrections are based on a so-called response, which is a ratio between the energy of particles right after the simulated collision, and the energy of those same particles after they are simulated to interact with the detector material. The first aim of this thesis is to develop software tools that can closely investigate jet response after each step in the calibration. Furthermore, all jet analyses are dependent on the uncertainty of the jet calibration. A major contribution to this is the uncertainty of particles called kaons (K^0_L), which is currently conservatively estimated to 20% over the entire jet transverse momentum (pT) range. Therefore, the main aim of this thesis is to use the tools developed in order to derive a new improved K^0_L uncertainty. This is done by looking at how the K^0_L response changes depending on what models are used to simulate the particle interactions with the detector material. Based on the comparison of the K^0_L response from different interaction models, this thesis derives an improved K^0_L response uncertainty of 20% for pT<10 GeV, 10% for 10