Tau lepton reconstruction with energy flow and the search for <em>R</em>-parity violating supersymmetry at the ATLAS experiment

Abstract

The ATLAS experiment at the Large Hadron Collider (LHC) is measuring proton-proton collisions at a centre-of-mass energy of √s=7 TeV since 2010, an energy never reached before in collider experiments. A wide variety of measurements within and beyond the framework of the Standard Model of Particle Physics are performed. Supersymmetry (SUSY) is a widely studied extension of the Standard Model. In order to keep the parameter space of the minimal supersymmetric extension of the Standard Model (MSSM) phenomenologically manageable one often uses simplifying assumptions like minimal supergravity (mSUGRA). Additionally, almost all SUSY studies of the ATLAS collaboration assume the conservation of R-parity, which leads to a stable, weakly interacting lightest supersymmetric particle (LSP).<br /> This thesis investigates the discovery potential of the ATLAS experiment for R-parity violating (RPV) SUSY models in the framework of mSUGRA, where the stau is the LSP. Hence, the LSP is charged and decays in contrast to R-parity conserving models.<br /> Monte Carlo simulations of the detector are essential for all studies in the ATLAS experiment. The ATLAS fast track simulation FATRAS is a new approach for the Monte Carlo simulation of particles in the tracking systems. Its results are compared to first data at √s=900 GeV. Additionally, two generic detector simulations are compared to the full simulation of the ATLAS detector.<br /> The reconstruction of hadronic decays of tau leptons is crucial for the reconstruction of the stau mass in the considered model, but also of general interest for many searches for new physics with ATLAS. In this thesis the reconstruction of tracks for particles from tau decays is studied. A novel method, PanTau, is presented for the tau reconstruction in ATLAS. It is fully based on results of the energy flow algorithm eflowRec. Its performance is evaluated in Monte Carlo simulations. The dependency of the identification variables on the jet energy are studied in detail. Finally, the energy flow quantities and the identification variables are compared between Monte Carlo simulations and measured QCD jet events with first ATLAS data at √s=7 TeV.<br /> For the first time in the framework of this RPV model a detailed signal to background analysis is performed for a specific benchmark scenario using a full Monte Carlo simulation of the ATLAS detector. The parameter space in the neighbourhood of this benchmark scenario is investigated in a parameter scan. The discovery reach with the first data of the ATLAS experiment is estimated. Furthermore a feasibility study for an estimate of the stau LSP mass is given.