First search for electroweak supersymmetry in final states with hadronic decays of WW, WZ, or WH boson pair and missing transverse momentum

This dissertation presents a new search for particle physics beyond the standard model in the form of electroweak production of supersymmetric particles, specifically charginos and neutralinos. The novel search is performed using Run~2 data from the CMS experiment at the LHC with a total integrated luminosity of 137 fb$^{-1}$. The targeted final states include a pair of bosons (WW, WZ, or WH) with large missing transverse momentum arising from the lightest neutralinos ($\widetilde{\chi}$$_{1}^{0}$). Deep neural network large-radius jet taggers are used to identify hadronic decays of the bosons. The standard model backgrounds are estimated using data-driven techniques. No significant excess of events is observed relative to expectations from the standard model. Results are presented in terms of constraints on the cross sections for production of mass-degenerate wino-like superpartners of SU(2) gauge bosons, $\widetilde{\chi}$$_{1}^{\pm}$/$\widetilde{\chi}$$_{2}^{0}$, and higgsino-like supersymmetric particles, $\widetilde{\chi}$$_{1}^{\pm}$/$\widetilde{\chi}$$_{2}^{0}$/$\widetilde{\chi}$$_{3}^{0}$, in both cases with the bino-like superpartner of U(1) gauge boson as the lightest supersymmetric particle. In the wino-bino scenario, wino masses are excluded up to 960 GeV. In the higgsino-bino scenario, the search excludes higgsino masses from 300 to 650 GeV. These exclusions are most stringent to date set by the CMS experiment. Sensitivity projections with future high-luminosity LHC data are also presented.