Three-Dimensional Imaging of the Nucleon Transverse Spin Structure

PI Yong Zhao, Argonne National Laboratory
Co-PI Dennis Bollweg, Brookhaven National Laboratory
Peter Boyle, Brookhaven National Laboratory
Xiang Gao, Brookhaven National Laboratory
Jinchen He, University of Maryland, College Park
Swagato Mukherjee, Brookhaven National Laboratory
Qi Shi, Brookhaven National Laboratory
Fei Yao, Brookhaven National Laboratory
Rui Zhang, Argonne National Laboratory
Award INCITE
Hours 1,000,000 Aurora Node-Hours
Year
Domain Physics
A green sphere representing a quark sits inside of a halved concave orange sphere representing a proton. A large yellow arrow piercing through the orange shell denotes the motion of the proton, and corkscrewing yellow commets to the right of the proton represent its spin.

Graphic showing the transverse motion of a quark (green sphere) inside a proton whose spin is aligned to its direction of motion (large yellow arrow). Credit: Valerie Lentz/Brookhaven National Laboratory

Project Summary

This project performs the first lattice QCD calculation of transverse-momentum–dependent parton distributions for a transversely polarized nucleon, enabling 3D imaging of its transverse spin structure. The results will provide essential theoretical input for hadron physics experiments.

Project Description

Quarks and gluons are the building blocks of protons and neutrons, collectively called nucleons. They are bound inside nucleons by the strong nuclear force, or quantum chromodynamics (QCD), which is also responsible for the formation of atomic nuclei and, as such, over 99% of visible matter in our universe. Central questions in QCD include uncovering the origin of the proton's mass and spin and understanding how QCD governs the confined motion and spatial distribution of quarks and gluons within the nucleon. These fundamental questions can all be profoundly informed by precise multi-dimensional imaging— tomography—of the proton. This endeavor lies at the heart of the scientific missions of the United States' flagship hadron physics facilities: Jefferson Lab and the forthcoming Electron- Ion Collider, which is to be constructed at Brookhaven National Laboratory. 

This project will carry out the first lattice QCD calculation of the transverse-momentum- dependent partonic structure of a nucleon transversely polarized relative to its direction of motion. Specifically, this project will compute the quark transversity, worm-gear, and pretzelosity transverse-momentum parton distributions in 3D momentum space–key observables for imaging the transverse spin structure of the nucleon. To date, phenomenological knowledge of these distributions remains limited; thus, the calculations will provide critical theoretical input and predictive guidance for experiments at the Jefferson Lab 12 GeV upgrade and the future Electron-Ion Collider. These results will significantly advance our understanding of the origin of transverse proton spin and contribute to a comprehensive 3D tomography of the nucleon.

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