Investigating the Quantum Properties of Jets and the Search for a Supersymmetric Top Quark Partner with the ATLAS Detector

Quarks and gluons are the fundamental building blocks of matter responsible for most of the visible energy density in the universe. However, they cannot be directly observed due to the confining nature of the strong force. The Large Hadron Collider (LHC) uses proton-proton collisions to probe the highest energy reactions involving quarks and gluons happening at the smallest distance scales ever studied in a terrestrial laboratory. The observable consequence of quark and gluon production in these reactions is the emergent phenomenon known as the jet: a collimated stream of particles traveling at nearly the speed of light. The quantum properties of the initiating quarks and gluons are encoded in the distribution of energy inside and around jets. These quantum properties of jets can be used to study the high energy nature of the strong force and provide a way to tag the hadronic decays of heavy boosted particles. The ATLAS detector at the LHC is well-suited to perform measurements of the internal structure of high energy jets. A variety of novel techniques utilizing the unique capabilities of the ATLAS calorimeter and tracking detectors are introduced in order to probe the experimental and theoretical limits of the quantum properties of jets. Studying quarks and gluons may also be the key to understanding the fundamental problems with the Standard Model (SM) of particle physics. In particular, the top quark has a unique relationship with the newly discovered Higgs boson and as such could be a portal to discovering new particles and new forces. In many extensions of the SM, the top quark has a partner with similar relationships to other SM particles. For example, a scalar top partner (stop) in Supersymmetry (SUSY) could solve the Higgs boson mass hierarchy problem. Miraculously, a SUSY neutralino could also account for the dark matter observed in the universe and may be copiously produced in stop decays. High-energy top quarks from stop decays result in jets with a rich structure that can be identified using the techniques developed in the study of the quantum properties of jets. While there is no significant evidence for stop production at the LHC, the stringent limits established by this search have important implications for SUSY and other models.