CAREER: The Three-Dimensional Structure of the Proton

This award is funded in whole or in part under the America Rescue Plan Act of 2021 (Public Law 117-2).

Protons and neutrons are the basic building blocks of almost all visible matter, and account for 95% of the mass of the visible universe. Protons and neutrons are composed of smaller particles, quarks, bound together by the strong nuclear force, which is carried by gluons and is responsible for all nuclear matter, from hydrogen ions to neutron stars.

The exact arrangement of quarks and gluons inside protons and neutrons is not well known. This project helps understand the three-dimensional arrangement of gluons within protons and neutrons. The PI uses large-scale supercomputing facilities to calculate the distribution of gluons inside protons and neutrons.

These calculations complement data on proton and neutron structure obtained from experiments performed at Thomas Jefferson National Accelerator Facility and the future Electron-Ion Collider at Brookhaven National Laboratory. The PI mentors students carrying out this research, is developing a graduate level course on computational methods for the strong nuclear force, and works with undergraduate students to create interactive physics simulations for a broad audience.

This project calculates the three-dimensional structure of gluons within protons and neutrons, by using first principles calculations of quantum chromodynamics (QCD), the theory of the strong nuclear force. At energies relevant to proton and neutron structure, QCD is strongly coupled and cannot be solved analytically. Lattice QCD, in which QCD is formulated on a discrete lattice and correlation functions are computed stochastically using Monte Carlo methods, provides a systematic approach to determining the properties of protons, neutrons, and other strongly-bound particles.

The project determines the gluon generalized distribution functions (GPDs) of the proton, which quantify the three-dimensional arrangement of gluons within the proton, using lattice QCD calculations. In addition, the project will calculate correlations between gluon and quark structure. These calculations complement experimental data on proton and neutron structure obtained from experiments at Thomas Jefferson National Accelerator Facility and at the future Electron-Ion Collider at Brookhaven National Laboratory, and provide a basis for combining experimental and theoretical data in a consistent framework.

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.