Measurement of $W^{+}W^{-}$ production cross section in proton-proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

This thesis presents a measurement of $W^{+}W^{-}$ production cross section with the $\textit{pp}$ collision data collected at the ATLAS detector in the year of 2015. The dataset corresponds to a centre-of-mass collision energy of $\sqrt{s} = 13$ TeV with a total integrated luminosity of 3.16 $\rm fb^{-1}$. The $W^{+}W^{-}$ signal events are selected using a signature where one of the $W$ bosons decays into an electron and an electron neutrino while the other produces a muon with an associated muon neutrino. The measured cross section in the chosen fiducial phase space close to detector acceptance is \begin{equation} \sigma^{\mathrm{fiducial}}_{W^{+}W^{-}} = 529 \pm 20 \, (\rm stat.) \pm 50 \, (\rm syst.) \pm 11 \, (\rm lumi.) \,\rm fb. \end{equation} The result within the assigned uncertainties is compatible with the best available Standard Model prediction of $478 \pm 17$ fb. The observed kinematic spectrums of the produced leptons from the decay of the two $W$ bosons are further investigated to study the triple gauge boson couplings at the $WW\gamma$ and $WWZ$ vertices. The deviation of these couplings from the Standard Model can probe the existence of new physics. The confidence intervals have been calculated for the parameters representing these anomalous couplings. The observations are consistent with the Standard Model expectations.