Search For Heavy Neutral Resonances In Vector Boson Fusion In Proton-proton Collisions At (?)?13 TeV With The ATLAS Detector At The LHC

The vector boson fusion (VBF) is an important class of processes in the standard model (SM), and the studies of this process have an especially important physical mean-ing. First of all, the VBF process can be used to directly examine the electoweak sym-metry breaking (EWSB) mechanism of the SM. In the SM, without the existence of Higgs boson, the scattering amplitude of longitudinally polarized W or Z boson in-creases unboundedly with energy and violates the unitarity at TeV scale. Thus the VBF process could provide a unique means to directly test the EWSB mechanism. Secondly,the VBF process is very sensitive to new physics. Although a Higgs boson with a mass of around 125 GeV has been discovered at the Large Hadron Collider (LHC), it is still unknown whether this discovered particle fully or only partially unitarizes the amplitude of the VBF process, and new resonances may be needed to help restore the unitarity.Last but not the least, if the new resonances have no or weak coupling to fermions, the VBF process would be a leading channel for these resonances search.This thesis presents two searches for heavy neutral resonances produced through vector boson fusion using the proton-proton (pp) collision data collected at (?) = 13 TeV with the ATLAS detector at the LHC. The first search for heavy neutral reso-nances (R) produced through qq?Rqq?e+ve-vqq(e = e,?)is performed us-ing pp collision data corresponding to an integrated luminosity of 3.2 fb-1 recorded in 2015. No significant data excess above the SM background prediction is observed.The upper limits at the 95% confidence level (CL) are set on ?R × B(R?evev) for five types of new resonances predicted by a benchmark model of an electroweak chi-ral Lagrangian (EWChL). The other search for heavy neutral resonances (X) produced through qq? Xqq? WWqq ? ev?vqq is performed using pp collision data corre-sponding to an integrated luminosity of 36.1 fb-1 collected in full 2015 and 2016. No evidence of such heavy neutral resonances is found in the mass range between 200 GeV and up to 3 TeV. The 95% CL upper limits are set on ?x × B(X?WW) for several signal models predicting the scalar, vector and tensor resonances.For these works presented in this thesis, the VBF productions in fully-leptonic decay channels (ee, ??, e?) are first used in the ATLAS experiment to search for new scalar, vector and tensor resonances predicted by several theoretical models. The first sets of 95% CL upper limits are obtained on the production cross section times branching ratio of these new resonances produced through vector boson fusion.