Precision Higgs Coupling Measurements in $H \to W W^* \to \ell \nu \, \ell \nu$ Final State with the ATLAS Detector at the LHC

The Standard Model (SM) is a gauge theory that describes the fundamental particles of matter and the forces between these particles. It has been tested to a very high precision in the past several decades, except for observation of the Higgs particle, a ramification of the Higgs mechanism. After discovery of the Higgs particle in July 2012, at the Large Hadron Collider (LHC) at the European organization for Nuclear Research (CERN), subsequent studies have focused on confirming whether the newly discovered particle is consistent with the SM Higgs. In particular its spin and its couplings have been measured. In this thesis, the Higgs coupling properties are measured using H->WW*->lvlv; final state. The H->WW*->lvlv channel has a large branching ratio, thus, it provides a large amount of Higgs signal and more precise Higgs property measurements. The overall significance is 6.1 sigma while the expected significance is 5.8 sigma at the Higgs mass mH = 125.36 GeV. The overall signal strength is measured as mu = 1.09+0.23-0.21 while mu_ggF = 1.02+0.29-0.26 and mu_VBF = 1.02+0.53-0.45. The results of the signal strength are used mu to measure the Higgs coupling to fermions and to gauge bosons under the SM Higgs hypothesis. The measured Higgs coupling constant to fermions is kappa_F = 0.93+0.32-0.23 and to boson is kappa_V = 1.04 ±0.11. This study also measures the inclusive cross-sections for the gluon-gluon fusion (ggF) and the vector boson fusion (VBF) production modes as well as the fiducial cross-sections of a ggF signal region in H->WW*->lvlv events.