Identifying fake leptons in ATLAS while hunting SUSY in 8 TeV proton-proton collisions

For several theoretically and experimentally motivated reasons, super- symmetry (SUSY) has for some time been identified as an interesting candidate for a theory of fundamental particle physics beyond the Stan- dard Model. The ATLAS collaboration, of which I am a member, possess a detector emplaced in the Large Hadron Collider experiment at CERN. If SUSY does in fact describe our universe, then it is hoped that evidence of it will be visible in data collected in the ATLAS detector. I present an analysis looking for a particular signature that could indicate the presence of SUSY; events containing two like-charge leptons (e or μ). This signature benefits from having both low Standard Model backgrounds as well as potential to observe several SUSY scenarios, par- ticularly those involving strong production processes. These include pair production of squarks and gluinos. The latter of these are particularly relevant for the analysis presented herein since gluinos are Majorana fermions; hence they can decay to produce like-charge leptons. The analysis considers several SUSY production topologies determined from a variety of simplified and phenomenological models. One of the core pieces of any ATLAS analysis is estimating the expected backgrounds in the signal regions. These backgrounds arise both from known Standard Model production processes that can produce the same final state as the SUSY models being targeted, as well as detector mismeasurement effects. One important background in the like-charge analysis is that of “fake” leptons; these are jets that have been misclassified as either electrons or muons by the reconstruction algorithms. A large portion of this thesis is dedicated to introducing novel techniques for robustly estimating these backgrounds, and evaluating their relative performance.