Electroweak production of Z boson with two jets and determination of heavy boson densities

Abstract

In this thesis the electroweak production of the Z boson in association with two jets is investigated focusing on its topology via the Vector Boson Fusion (VBF) mechanism and the determination of heavy boson parton densities.

The first part presents a theoretical study of the Drell–Yan and electroweak~$Zjj$ production mechanisms and their particle-level comparison, demonstrating the dominance of the former and motivating the definition of a VBF-enhanced phase space to isolate electroweak contributions. The impact of electroweak corrections is discussed as a motivation for introducing electroweak (heavy boson) densities. These densities, derived from extended DGLAP evolution equations, are successfully validated using HERA DIS data and applied to VBF Z production to assess their relevance for t-channel boson dynamics and future collider studies.

The second part reports fiducial and differential cross-section measurements of Z-boson production with dijets in the \(Z \rightarrow e^+e^-\), \(Z \rightarrow \mu^+\mu^-\) channels and the combination of both, analysed within a common phase space. Both inclusive (QCD~$Zjj$ + EW~$Zjj$) and electroweak (EW~$Zjj$) components are measured as functions of the dilepton transverse momentum, \(p_T^{ll}\). The inclusive measurement uses 59.83~fb\(^{-1}\) of 13~TeV CMS data from 2018, while the main result, the electroweak~$Zjj$, exploits the full Run~2 dataset of 138~fb\(^{-1}\) at \(\sqrt{s}=13\)~TeV. The Run~2 electroweak~$Zjj$ measurement achieves a total precision of about \(6\%\), establishing a new benchmark for EW~$Zjj$ studies.