Multi-Hadron Interactions using Lattice QCD with the Stochastic LapH Method and QUDA

Protons and neutrons, which make up atomic nuclei, are comprised of fundamental particles known as quarks and gluons, whose interactions are described by quantum chromodynamics (QCD). QCD and the electroweak force should describe all nuclear processes, thereby explaining the inner workings of stars and the abundance of hydrogen versus helium and other elements in the universe. QCD also suggests that many other types of composite particles, known as hadrons, should exist in Nature as unstable resonances. Extracting such information from QCD is difficult, requiring large-scale computer simulations. QCD predictions of the structure of the proton and neutron, scattering involving one particular hadron known as a Delta baryon, and other heavier hadronic resonances will be investigated using supercomputing resources. The proposed research lends support to current experiments, such as the GlueX experiment in Hall D at the Thomas Jefferson National Accelerator Facility (JLab). The scattering information involving the Delta baryon will be crucial for current and future experiments studying neutrinos, an important elementary particle that permeates the universe. The PI will mentor a graduate student engaged in this research, and the graduate student will also receive training in the use of state-of-the-art parallel computing resources. The physics of hadron-hadron interactions will be studied by formulating QCD on a space-time lattice so that computer calculations of a variety of QCD correlation functions involving quark and gluon fields can be carried out. Nucleon-pion, nucleon-nucleon, and nucleon-hyperon scattering phase shifts will be investigated, yielding important information on hadron structure. Studies of three-meson systems will be continued to better understand certain nuclear reactions and meson resonances, such as the omega meson, which have significant three-body decay branching ratios. Scattering processes involving nucleon-pion-pion states will be considered in order to understand heavier baryon resonances, such as the Roper resonance. Form factors involving the nucleon and transitions through the Delta baryon will be a particular focus since they are crucial to accelerator-based neutrino experiments, such as the Deep Underground Neutrino Experiment (DUNE). Past work used a computational technique known as the stochastic Laplacian Heaviside (LapH) method, which made possible such computations in lattice QCD for the first time. Recent development of new software exploiting GPU accelerations has opened up the possibility of making exact LapH studies feasible, allowing unprecedented statistical precision of the results obtained. 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.