HET Seminar

Abstract:

More than 99% of the mass of the visible matter resides in hadrons which are bound states of quarks and gluons, collectively called partons. These are the fundamental constituents of Quantum Chromodynamics (QCD), the theory of strong interaction. While QCD is a very elegant theory, it is highly non-linear and cannot be solved analytically, posing severe limitations on our knowledge for the structure of the hadrons. Lattice QCD is a powerful first-principle formulation that enables the study of hadrons numerically, which is done by defining the continuous equations on a discrete Euclidean four-dimensional lattice.

The proton structure is among the frontiers of Nuclear and Particle Physics both experimentally and theoretically. From the theory side, lattice QCD is a vital component for the physics program of the future Electron-Ion-Collider to be built at Brookhaven National Laboratory. Parton distribution functions (PDFs) and their generalizations (GPDs, TMDs) have a central role in understanding the hadron structure and have been under investigation both experimentally and theoretically for several decades. Their direct calculation in lattice QCD poses challenges; information is accessible through their Mellin moments. However, novel approaches to extract their x-dependence using matrix elements of non-local operators have been proposed and extensively investigated in recent years.

In this talk, we will demonstrate the advances in extracting PDFs and GPDs from lattice QCD using novel approaches, in an effort to map the three-dimensional structure of the proton. We will discuss the strengths of lattice calculations, but also identify the challenges associated with the elimination of systematic uncertainties.