Constraining Higgs Boson Self-coupling with VHH Production and Combination, and Searching for Wgamma Resonance using the CMS Detector at the LHC

Abstract

Since the discovery of the Higgs boson (H) with a mass of 125 GeV by the ATLAS and CMS collaborations at the CERN LHC in 2012, the focus of the particle physics community has expanded to include precise measurements of its properties, and so far the measurements align with the Standard Model (SM) predictions. Of particular interest among these properties is the Higgs boson self-coupling, which can be directly probed by measuring the cross section for the production of Higgs boson pair (HH). This thesis presents three analyses using proton- proton collision data at \sqrt{s} = 13TeV with an integrated luminosity of 138 fb−1: a search for SM Higgs boson pair production with one associated vector boson (VHH), a combination of H measurements and HH searches, and a search for a new particle decaying to a W boson and a photon (\gamma). The VHH search focuses on Higgs bosons decaying to bottom quarks, and vector boson decaying to electrons, muons, neutrinos, or hadrons, with a novel background estimation approach. An observed (expected) upper limit on the VHH production cross section is set at 294 (124) times the SM predicted value. The combination of H measurements and HH searches aims to constrain the Higgs self-coupling with the best possible precision. The search for Wgamma resonance focuses on leptonic W boson decays, achieving the world’s best sensitivity for this resonance in the mass ranges considered.