A Measurement of $\boldsymbol{W}$ Boson Pair Production in $\boldsymbol{pp}$ Collisions at $\sqrt{s}=8$ TeV with the ATLAS Experiment

In this thesis, measurements of the $W$ boson pair production cross section in proton-proton collisions at a centre-of-mass energy of 8 TeV are presented. A dataset corresponding to an integrated luminosity of $22.3~\mathrm{fb}^{-1}$ recorded by the ATLAS experiment in the year 2012 is used. The $W$ bosons are identified by their decay products of exactly two leptons with opposite electrical charge, electrons or muons, and missing transverse momentum induced by their corresponding neutrinos. First, a measurement restricted to final states without hadronic jets is presented and differential fiducial cross sections, total cross sections and limits on anomalous triple gauge boson couplings are obtained. A second measurement of the fiducial cross section in association with exactly one hadronic jet is presented. The ratio of fiducial cross sections for different jet multiplicities is reported and the combined fiducial cross section is extrapolated to the total phase space. The total cross section is found to be $68.2 \pm 1.2 \text{(stat)} \pm 3.4 \text{(syst)} \pm 2.8 \text{(theo)} \pm 1.4 \text{(lumi)}~\text{pb}$, in agreement with the corresponding theoretical calculation of $65.0 \pm 1.2~\text{pb}$.