A New Era for Lattice QCD: Unveiling the Mysteries of a Proton

Temple University, Philadelphia PA

Investigators

Abstract

More than 99% of the mass in the visible Universe resides in hadrons (neutrons and protons), which are bound states of quarks and gluons, the fundamental constituents of Quantum Chromodynamics (QCD). QCD is the theory governing the strong force responsible for the binding of protons and neutrons into atomic nuclei. QCD describes successfully a wide range of complex processes, from sub-nuclear interactions to macroscopic phenomena, such as the state of matter in the early Universe. In this context, the proton, one of components of the atomic nucleus, represents an ideal laboratory for studying the dynamical properties of QCD. This project will investigate theoretically non-perturbative quantities that encapsulate the dynamics of quarks and gluons within the proton. Ab initio calculations will be performed in Lattice QCD (LQCD), a rigorous framework for studying the proton structure that requires numerical solutions of the QCD equations on supercomputers. A graduate student will be engaged in cutting-edge fundamental research, ensuring his/her emergence as an independent researcher. The project will also support outreach activities promoting science to K-12 students. This research program will undertake calculations within LQCD using state-of-the-art simulations and modern techniques. The simulations will be performed with quark masses fixed to their physical values, the latest achievement of the field. The class of observables that will be computed are the scalar, axial and tensor charges for both valence and sea quarks, as well as the axial and electromagnetic form factors. The scientific objectives are two-fold: Reproduce observables that are well-known experimentally, as a benchmark of the formalism, which will then allow for predictions of lesser-known or difficult to measure quantities; the latter is expected to impact New Physics searches. Quantities of the former kind are the axial and electromagnetic form factors, while quantities of the latter kind are the scalar and tensor interactions that could signal Physics beyond the Standard Model. The project aims at high-precision results and quantifiable systematics, so that the outcome of these computations yield high-credibility predictions of observables. This project will result in a better understanding of the proton structure, will be valuable for the interpretation and guidance of experiments, and may shed light on long-standing puzzles in nuclear physics, such as the proton spin.