Exploring Hadron Structure Through Monte-Carlo Fits and Model Calculations

Abstract

Since the discovery in the 1960's that the proton is not a fundamental particle but instead composed of even smaller particles known as quarks and gluons, there has been a concerted effort to understand the proton's internal structure. There still remain many mysteries about the proton and the theory that describes the interactions within: Quantum Chromodynamics (QCD). The distributions of quarks and gluons are encoded in objects known as parton correlation functions. Physicists use high-energy scattering experiments to access these functions by means of QCD factorization. This process of extracting information is known as a global QCD analysis. Further insight can be gained through first-principles calculations in lattice QCD as well as models for the strong interaction. In this thesis, we will use global QCD analyses to provide information on the one-dimensional (1D) structure of the proton using the latest experimental data available. Among the mysteries that remain within the proton, we provide insight on the non-perturbative nature of the proton's sea quarks, for both cases where the proton is unpolarized and longitudinally polarized. We also bring new information on the "proton spin puzzle," which concerns the delegation of the proton's spin into its constituent quarks and gluons. We shed light on the proton's transversely polarized structure, where current results from global QCD analyses and lattice QCD fail to paint a consistent picture. Our analyses also reveal a new feature of nuclear effects within light, highly asymmetric nuclei such as helium and tritium. Finally, we perform derivations in a spectator diquark model to glean information on the proton's 3D structure, and calculate moments that can be used in future lattice QCD studies.