Bridging grant application for ATLAS-Canada: Electroweak multi-boson interactions at the Large Hadron Collider

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The Standard Model (SM) of particle physics provides the current best description of elementary particles and their interactions. However, there are many phenomena that are outside the scope of the SM. Particle interactions are mediated by four forces: strong, weak, electromagnetic, and gravitational. The strong, weak, and electromagnetic forces are mediated by so-called gauge bosons: gluons, W and Z bosons, and photons, respectively. At the high energies probed in proton-proton collisions at the Large Hadron Collider (LHC) at CERN, the weak and electromagnetic forces are unified into the electroweak force. The LHC allows us to probe the intricate details of electroweak interactions at the highest-ever energy scales with unprecedented precision. Furthermore, the required extensions to the SM to explain dark matter and the matter-antimatter asymmetry of the universe are intimately tied to modifications of SM electroweak interactions, and the LHC provides the richest environment in which to probe these interactions. This grant will enable me to lead a new research programme at the LHC to answer fundamental questions about electroweak interactions. The production of multiple gauge bosons in electroweak interactions in pp collisions is extremely rare but precisely predicted by the SM. As such, any existing multi-boson measurements are currently limited in experimental precision, and our understanding of these processes is markedly limited. It is therefore possible that new physics phenomena that couple to these particles could be revealed through the study of such processes. New particles at the TeV energy scale, out of reach from direct searches at the LHC, can alter the rate or kinematics of multi-boson processes. I will spearhead the effort to perform a combined effective field theory fit of the three measurements that are sensitive to the interaction between two W bosons and two photons. This combination will provide optimal sensitivity to any as-of-yet undiscovered particles, as well as showing any areas where such particles could be hidden from our searches. Identifying these uncovered areas will help inform our future measurements - and preparations for Run 3. Additionally, I will contribute to the ATLAS Trigger software for Run 3 and beyond. I have worked on the trigger since January 2017, and have made significant contributions towards increasing the breadth of signal topologies we recorded in Run 2. In Run 3, the high-level trigger software will run multithreaded, and a significant amount of work is necessary to complete and commission the software. I will work on designing and optimizing the overall event selection for Run 3 to ensure we can maintain the overall high quality of data ATLAS recorded in Runs 1 and 2.