Search for a Heavy-philic W' Boson using Proton-Proton Collisions at Center-of-Mass Energy of 13 TeV Using the ATLAS Detector

Abstract

This thesis presents a search for a new, hypothetical particle predicted by theories extending the Standard Model of particle physics. This heavy $W'$ boson interacts only with the heaviest known quarks, top and bottom (heavy-philic). Such a particle could provide insight into the fundamental forces of nature and be the first hint at extra dimensions or a composite Higgs. The $W'$ boson is produced in high-energy proton-proton collisions, mainly through gluon fusion. Its decay leads to a distinctive final state: $tbW'\rightarrow tbtb$. This search uses data collected by the ATLAS detector during Run 2 at the Large Hadron Collider, focusing on events with a single charged lepton, at least five jets, and at least three jets identified as originating from bottom quarks. To improve sensitivity to this rare process, advanced machine learning techniques are applied. A profile likelihood fit to the machine learning output is used to evaluate the data. No significant excess above the Standard Model background is observed, and exclusion limits are set at the 95\% confidence level on the production cross-section of the heavy-philic $W'$ boson.