Higgs Spin Determination and Unitarity of Vector-boson Scattering at the LHC

Abstract

After the discovery of a new particle at the Large Hadron Collider (LHC), it is crucial to definitely verify or disprove whether this new 125 − 126 GeV resonance is the Higgs boson of the Standard Model (SM). Thus, its features, including its spin, have to be determined. In order to distinguish the two most likely spin hypotheses, spin-0 or spin-2, the phenomenology of light spin-2 resonances produced in different gluon-fusion and vectorboson-fusion processes at the LHC is studied. Starting from an effective model for the interaction of a spin-2 particle with SM gauge bosons, cross sections and differential distributions are calculated within the Monte Carlo program Vbfnlo. Whereas with specific model parameters, such a spin-2 resonance can mimic rates and transverse-momentum distributions of a SM Higgs boson in the main decay channels γγ, WW and ZZ, several distributions allow to separate spin-2 from spin-0, almost independently of model parameters. Since the SM Higgs boson ensures the unitarity of the S-matrix in vector-boson scattering, another topic of this thesis is to investigate if the capability of unitarizing vector-boson scattering is a unique feature of the spin-0 Higgs boson or if particles with a different spin, i.e. spin-1 or spin-2, are able to perform the same task. Furthermore, the characteristics of heavy spin-2 resonances in vector-boson-fusion processes are analyzed at NLO QCD accuracy in order to facilitate the spin determination of heavy particles that might be detected at the LHC.