Observation of the electroweak production of two $W$ bosons with the same electric charge in association with two jets in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

This dissertation presents the observation of $W^{\pm}W^{\pm}$ electroweak production in proton-proton collisions with a center-of-mass energy of 13 TeV at the Large Hadron Collider using the ATLAS detector. The $W$ bosons are required to decay leptonically, giving a signature of two leptons (electrons or muons) with the same electric charge, two jets with a large invariant mass and rapidity separation, and missing transverse energy. The $W^{\pm}W^{\pm}$ electroweak fiducial cross section is measured using $36.1 ~\textrm{fb}^{-1}$ of data recorded in 2015 and 2016. A total of $122$ candidate events are observed with a fitted background of $69\pm7$ events, corresponding to an observed signal significance of 6.5 standard deviations. The measured fiducial cross section is $\sigma_{\textrm{fid}}=2.89^{+0.51}_{-0.48}(\textrm{stat})^{+0.29}_{-0.28}(\textrm{syst})$ fb and is in agreement with Standard Model predictions.