First Observation of Associated Production of J/$\psi$ meson and W boson

Particle physics concerns the understanding of the fundamental building blocks of nature, the production of particles and their interactions. The experimental study of high energy collisions allows us to probe the theoretical predictions pertaining to particles. The Large Hadron Collider was built on the outskirts of Geneva, to accelerate and collide protons at the highest energies ever, and allow for the study of the products of these collisions. The ATLAS detector is designed to detect the particles resulting from the proton–proton collisions and collect the data for further study. The discovery of the $J/\psi$ meson in 1974 paved the way for the presence of three families of quarks in the Standard Model of Particle Physics. The production mechanism of $J/\psi$ at the LHC is not well understood, and several models have been proposed to explain it, such as the Color Singlet and Color Octet models. The associated production of $J/\psi$ meson with a W boson offers an additional insight on the production of $J/\psi$. In this thesis, we report the first observation of the $W^{\pm} + J/\psi$ production using 4.5 fb$^{-1}$ of ATLAS data from proton–proton collisions at center of mass energy of 7 TeV at the Large Hadron Collider. In addition, we measure the cross-section ratio of the $W^{\pm} +J/\psi$ production to the inclusive $W$ production. The results are dominated by statistical uncertainties and suggest that a combination of the different models for J/$\psi$ production is needed to explain $J/\psi$ production.