UC Santa Cruz

Supersymmetric extensions of the Standard Model of particle physics are theoretically motivated by their ability to potentially address some of the biggest unresolved questions in physics. However thus far there has been no conclusive evidence to support the idea that supersymmetry exists at the energy scales currently being probed by the experiments at the Large Hadron Collider. If supersymmetry does exist in nature, one reason that it may be evading experimental detection is that the production of supersymmetric particles is rare and difficult to distinguish from background processes. To overcome this challenge, thoughtful design of the analysis strategy is required.

This dissertation presents a search for the production of electroweak supersymmetric particles with compressed mass spectra utilizing a vector boson fusion topology. The search was conducted using 140 $\text{fb}^{-1}$ of data recorded with the ATLAS detector from proton-proton collisions at $\sqrt{s}$ = 13 TeV. The general search strategy involves selecting events characterized by significant missing transverse momentum, the presence of two forward jets that are consistent with a vector boson fusion signature, and a lepton veto to target models with compressed mass spectra. Additionally, a boosted decision tree algorithm is used to further improve the signal to background separation.

The results of the search show no evidence for supersymmetry, and no significant deviations are found between the prediction based on the Standard Model and the observed data. This search probes models that have yet to be excluded by previous searches and is able to extend existing limits for these compressed supersymmetric scenarios.