Studies of R-parity violating supersymmetry with the ATLAS detector

This thesis investigates signatures of R-parity violating (RPV) supersymmetry (SUSY) in the context of the ATLAS detector at the LHC. SUSY models in which R-parity is violated through the lepton-number violating $\lambda^{\prime}_{221}$ coupling are studied, focusing on two cases; in the first case the lightest supersymmetric particle (LSP) is a neutralino, and in the second case the LSP is a stau. Monte Carlo studies using the full ATLAS detector simulation are shown. It is predicted that RPV SUSY models with a stau LSP will often be characterised by a high $\tau$-lepton multiplicity in SUSY events. This thesis presents an investigation into the expected $\tau$-reconstruction performance in such models using simulated ATLAS data. The impact of the event topology associated with a non-zero $\lambda^{\prime}_{221}$ coupling on the $\tau$-reconstruction performance is discussed. The measurement of the neutralino mass is demonstrated for models with a neutralino LSP and non-zero $\lambda^{\prime}_{221}$ coupling. An exclusive method focusing on the reconstruction of $\tilde{\chi}^{0}_{1} \rightarrow \mu qq$ decays is demonstrated, using a data-driven method for estimating the combinatoric background. The extension of these methods to the case of a stau LSP with $\tilde{\tau}_{1} \rightarrow \mu qq \tau$ decays is also discussed. In addition, this thesis presents work involving aspects of both the experimental hardware and simulation software that are essential to physics analysis in ATLAS. Firstly, results from the analysis of some of the initial DAQ test data taken during the macro-assembly phase of the Semiconductor Tracker are shown. Secondly, the development of software tools for the fast simulation of $\tau$-reconstruction algorithms is described. Here, performance studies of the track-based $\tau$-reconstruction algorithm (tau1p3p) are presented with the results incorporated into the ATLFAST fast simulation package.