RUI: The 3D Momentum and Spin Structure of the Nucleon in QCD

The visible universe is made up of nucleons (protons and neutrons) and electrons. Nucleons themselves are interacting dynamical systems of partons, quarks, and gluons—the degrees of freedom of the theory of strong interactions, Quantum Chromo Dynamics (QCD). Unfolding the QCD quark and gluon structure of nucleons is a crucial area of study in modern nuclear physics. The main objective of this project is to advance theoretical and phenomenological studies of the three-dimensional (3D) momentum and spin structure of the nucleon in QCD. By doing this, the project aims to discover the internal landscape of the nucleon. This project expands the impact of the future program at the Electron-Ion Collider (EIC), a powerful new facility to be built in the United States, as well as of the existing programs at Jefferson Lab and Brookhaven National Laboratory, by performing phenomenological and theoretical studies, providing analysis, explanation of present data, and predictions for future measurements. The project contributes to the education of a diverse, globally engaged workforce with world-class skills by providing and developing courses on modern statistics and nuclear physics, organizing and teaching summer schools for graduate students, and running annual workshops on the 3D structure of the nucleon. The main objective of this project is to advance the theoretical and phenomenological studies of the 3D momentum and spin structure of the nucleon, and to map its internal landscape encoded in the Transverse Momentum Dependent parton distribution and fragmentation functions (TMDs). TMDs are crucial in understanding the correlations between the intrinsic motion and spin of partons and the nucleon, which generate Spin Asymmetries measured in various scattering processes. The project aims to extract the unpolarized 3D structure of the nucleon with high perturbative precision by performing a global QCD analysis of data from experiments from world facilities, including HERMES (DESY), COMPASS (CERN), Jefferson Lab, BELLE (KEK), BaBar (SLAC), BESIII (Beijing), RHIC (BNL), and LHC (CERN). The study involves a global QCD analysis of the data, unifying collinear and TMD physics. The project also focuses on studying the spin structure of the nucleon using all available world data, and extracting polarized TMDs such as Sivers functions, transversity, Collins Fragmentation Functions, and others. In addition, the project will combine TMD-related measurements and the polarized proton-proton scattering data from the Relativistic Heavy Ion Collider (RHIC, BNL) related to twist-3 factorization.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.