A Global View of Jets with the ATLAS Detector: From Hardware Triggers to Precision Measurements and Beyond

This thesis presents substantial work done on the ATLAS calorimeter hardware trigger upgrades and the results of two analyses. These all show the importance of understanding the hadronic final state in ATLAS at a global level. This is relevant from an experimental perspective which contributes to our ability to take data, and also helps to enable a thorough understanding of the Standard Model and searches of physics beyond the Standard Model. My work on the ATLAS hardware trigger encompasses significant contributions to the commissioning of the new module the global Feature Extractor (gFEX). This includes the full development of the gFEX Detector Control Systems, contributions to the custom operating system used in gFEX, and additional significant contributions to custom software written to interface with the gFEX firmware. The gFEX is now installed in ATLAS and triggering on real physics data in the ongoing Run 3. The two analyses documented in this thesis were performed using 139 inverse femtobarns of 13 TeV data taken with the ATLAS detector during Run 2. A search for supersymmetric partners of the Standard Model electroweak gauge bosons is presented first, and shows the significant gains in sensitivity possible by utilizing the high branching fractions of the fully hadronic final state. The precision measurement of Lund multiplicities in dijet events can help to constrain Monte Carlo models, and highlight important higher order effects missing from our current Monte Carlo models.