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

Abstract

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 LHC uses pp collisions to probe the highest energy reactions involving quarks and gluons happening at the smallest distance scales ever studied in a terrestrial laboratory. The quantum properties of the initiating partons are encoded in the distribution of energy inside and around jets. These quantum properties of jets (QPJ) 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 is well-suited to perform measurements of the 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 QPJ. Quarks and gluons may also be the key to understanding fundamental problems with the SM. 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. In many extensions of the SM, the top quark has a partner with similar properties. For example, a SUSY stop could solve The Hierarchy Problem. Miraculously, a SUSY neutralino could also account for the DM observed in the universe and may be copiously produced in stop decays. High-energy top quarks from stops result in jets with a rich structure that can be identified using the techniques developed in the study of the QPJ. 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. (adapted from the original to save characters)