Double Parton Scattering Contribution to the Same-Sign $W$ Boson Pair Production at ATLAS

This thesis investigates the feasibility of the double parton scattering measurement in high-energy proton-proton collisions using the ATLAS detector. In these processes, two or more distinct parton interactions proceed simultaneously in a single proton-proton collision at hard scales. The multiple parton interaction phenomenon is especially important for the exploration of the transverse structure of the colliding protons. The process under study is the production of a pair of $W$ bosons with the same electric charge, where both gauge bosons decay to a muon and an appropriate neutrino. Since the cross section is expected to be very small, this thesis focus on the description of the kinematic differences between the signal and background processes using the Monte Carlo simulations of proton-proton collisions at $\sqrt{s}$ = 14 TeV. The fiducial region found is considered to be the most suitable for the signal measurement. This thesis concludes that the LO cross section for the production of same-sign muon pairs in the studied ducial region is 8.7 fb, which also includes 1.1 fb of the signal process cross section. Therefore, the fraction of the double parton scattering events is expected to be around 13$\%$. This implies that the integrated luminosity necessary for the signal signicance of 5 standard deviations above the physics background is about 150 fb$^{-1}$.