"Synergy of High-Performance Computing and Nuclear Physics to resolve long-standing puzzles: the proton spin and mass decompositions"
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 interactions. Understanding hadron structure in terms of the constituent quark and gluons is among the frontiers of Nuclear and Particle Physics. The 2015 Nuclear Science Advisory Committee’s Long Range Plan for Nuclear Physics identifying a future US-based electron-ion collider (EIC) as the highest priority for new facility construction. In 2019, the National Academies of Sciences, Engineering, and Medicine (NAS) released an assessment report that strongly endorses the EIC science, and last year, the EIC has been approved by the DoE. The NAS report identified three high-priority science questions to understand the hadron structure: 1. How does the mass of the nucleon arise? 2. How does the spin of the nucleon arise? 3. What are the emergent properties of dense systems of gluons? The above questions are among the long-standing puzzles of Nuclear Physics, and progress in theory is equally important as the experimental efforts. While QCD is an exquisite theory, it is highly non-linear and cannot be solved analytically. This poses severe limitations on our knowledge of the hadrons' structure. 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 numerical simulations require large high-performance computing resources, and therefore, progress in lattice QCD cannot be achieved without access to supercomputing centers, state-of-the-art computer architecture, and improved algorithms. In this talk, I will discuss recent development in Lattice QCD related to aspects of the questions that the EIC will address, with the main focus being on the origin of the mass and the spin decomposition. I will show results for the proton, which provides an ideal system for studying QCD dynamics. I will discuss the strengths of lattice calculations and identify the challenges associated with eliminating systematic uncertainties.
