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 $WW^{(\ast)}\rightarrow\,\ell\nu\ell\nu$ 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.