Evidence of Higgs Boson Production through Vector Boson Fusion

The discovery of the Higgs boson in 2012 provided confirmation of the proposed mechanism for preserving the electroweak $SU(2) \times U(1)$ gauge symmetry of the Standard Model of particle physics. It also heralded in a new era of precision Higgs physics. This thesis presents a measurement of the rate at which the Higgs boson is produced by vector boson fusion in the \wwlnln decay channel. With gauge boson couplings in both the production and decay vertices, a VBF measurement in this channel is a powerful probe of the $VVH$ vertex strength. Using $4.5$~fb$^{-1}$ and $20.3$~fb$^{-1}$ of $pp$ collision data collected at respective center-of-mass energies of 7 and $8 \tev$ in the ATLAS detector, measurements of the statistical significance and the signal strength are carried out in the Higgs mass range $100 \leq m_H \leq 200 \gev$. These measurements are enhanced with a boosted decision tree that exploits the correlations between eight kinematic inputs in order to separate signal and background processes. At the benchmark Higgs mass of $125.36 \gev$, the significance of the data assuming the background-only hypothesis to be true has been observed to be $3.2\sigma$ ($2.7\sigma$ expected), constituting evidence of VBF Higgs boson production. The measured signal strength (ratio of observed cross section times branching ratio to that predicted by the SM) is $1.27^{+0.53}_{-0.45}$. The inclusive cross section times branching ratio is found to be $0.51^{+0.22}_{-0.17}$~pb at $\sqrts = 8 \tev$, consistent with the SM prediction of $0.34$~pb. No significant deviations from the SM predictions for VBF Higgs boson production are observed.