Nuclear physics theorists at the U.S. Department of Energy's Brookhaven National Laboratory have successfully demonstrated that supercomputers can predict the distribution of electric charges in mesons, which are particles composed of a quark and an antiquark. These predictions are crucial for future high-energy experiments at the Electron-Ion Collider (EIC), currently under construction at Brookhaven Lab.
Swagato Mukherjee, a theorist at Brookhaven Lab who led the research, stated, "The fundamental science goal of the EIC is to understand how the properties of hadrons, including mesons and more familiar protons and neutrons, arise from the distributions of their constituent quarks and gluons." The lightest meson, known as the pion, plays a significant role in binding protons and neutrons within atomic nuclei through nuclear strong force.
Recent predictions published in Physical Review Letters align with low-energy experiment measurements conducted at DOE’s Thomas Jefferson National Accelerator Facility. These predictions extend into higher energy levels anticipated for future EIC experiments. They will serve as a comparison basis when these experiments commence in the early 2030s.
Beyond establishing expectations for EIC measurements, scientists have used these predictions alongside additional supercomputer calculations to validate an approach called factorization. This method simplifies complex physical processes into two components or factors. Validating factorization will facilitate further EIC predictions and provide more reliable interpretations of experimental results.
The EIC will explore hadron composition by colliding high-energy electrons with protons or atomic nuclei. Virtual photons emitted from electrons act like microscopes revealing hadron properties. Scientists rely on factorization to convert precise collision measurements into detailed images of matter's building blocks within hadrons.
Factorization involves breaking down experimental measurements into two factors: one describing quark/gluon distribution inside hadrons and another detailing interactions between quarks/gluons with virtual photons emitted by colliding electrons. Solving quantum chromodynamics (QCD) equations requires simulating interactions on imaginary space-time lattices using powerful supercomputers.
To test factorization's validity, Qi Shi and Xiang Gao employed reverse calculations involving space-time lattice simulations for quark-antiquark distributions in mesons combined with simpler pen-on-paper calculations for photon interactions—resulting in predicted charge distribution values inside mesons matching previous independent supercomputer-calculated predictions perfectly.
Peter Petreczky emphasized that this work confirms factorization's effectiveness: "Scientists can now make use of future EIC data and factorization to infer other more complex quark and gluon distributions in hadrons that cannot be calculated—even using the most powerful computers."
This research received support from DOE Office Science (NP) along with computational resources provided by Argonne Leadership Computing Facility; Oak Ridge Leadership Computing Facility; National Energy Research Scientific Computing Center—all user facilities under DOE Office Science located respectively at Argonne National Laboratory; Oak Ridge National Laboratory; Lawrence Berkeley National Laboratory—and US Lattice Quantum Chromodynamics Collaboration facilities contributed partially towards computations involved therein.