Our primary research interests lie in perturbative Quantum Chromodynamics (QCD) and strong interactions, and their applications in high energy nuclear and particle physics. According to arXiv.org research category, our research falls under [hep-ph], or high energy physics - phenomenology, a branch of theoretical physics that explores the observable consequences of the fundamental particles, their interactions, and their emerging phenomena. Recently, we have also expanded our research into quantum computing applications for QCD-related problems. Our current research activities encompass four key areas:

Hadron Physics

Our main focus along this direction is the quantum tomography of nucleons, specifically understanding the QCD structure of the nucleon and spin physics. QCD, the theory of strong interactions, describes how elementary particles like quarks and gluons interact with each other and is responsible for how quarks and gluons make up of hadrons. While the fundamental laws of QCD are elegantly concise, decoding the structural complexity of protons and neutrons in terms of quarks and gluons governed by those laws remains one of the greatest challenges in physics today. This challenge drives the development of cutting-edge experimental facilities.

Through QCD factorization theorems, theorists can extract the low-energy properties of nucleon structure from the experimental data. In recent years, a multidimensional view of nucleon structure has emerged, offering profound new insights into the internal dynamics of QCD. These theoretical advancements address long-standing questions about the confined motion of quarks and gluons inside the nucleon: How do they move in both transverse and longitudinal planes? Do they exhibit orbital motion, contributing to orbital angular momentum? What are the quantum correlations between the motion of partons, their spin and the spin of the nucleon? These correlations have revolutionized our understanding of nucleon structure, providing new perspectives on how it manifests across various experimental measurements. 

The research is closely connected to experimental programs at Jefferson Lab, COMPASS, Belle, RHIC and the future Electron Ion Collider (EIC) at Brookhaven National Laboratory, which will further advance our understanding of hadron physics. 

QCD Collider Physics

Our main focus along this direction is the application of perturbative QCD and effective field theory techniques in high energy physics. Specifically, we leverage perturbative QCD and effective field theory, such as soft collinear effective theory (SCET), to study jets, jet substructure, and heavy flavor production - including both open heavy flavor mesons and heavy quarkonia. This research is closely aligned with experimental program at the LHC and RHIC.

Collimated jets of hadrons are a dominant feature in high energy particle interactions. These jets originate from the fragmentation of accelerated quarks and gluons, providing critical insights into their behavior at high energies. In recent years, jet and jet substructure measurements have become a powerful tool for studying the fundamental properties of QCD, probing the partonic structure of the proton, and extracting the strong coupling constant. Moreover, jets and their substructure offer promising new observables in the search for physics beyond the Standard Model (BSM).

At the same time, the research on heavy flavor production - including open heavy flavor meson, heavy flavor jet, and heavy quarkonium - remains one of the most active and fascinating areas of strong interaction physics. For example, heavy quarkonium production offers vital information about hadronization and fragmentation processes. Yet, despite more than forty years since the discovery of the J/ψ, the production mechanisms of heavy quarkonia are still not fully understood. Theoretical calculations in jets, jet substructure, and heavy flavor, with precision comparable to experimental results, are critical. A comprehensive understanding of these processes provides deeper insights into QCD dynamics is essential for advancing searches for new physics. Additionally, such understanding is a prerequisite for accurate interpretation of experimental data and progress in the field of BSM physics. 

Gluon Saturation and Heavy Ion Physics

Our main focus along this direction is gluon saturation, hard scattering in nucleus and heavy ion collisions. Ordinary nuclear matter is predicted to undergo a phase transition into a novel state under extreme temperature and density. This new state, known as the quark-gluon plasma (QGP), is composed of deconfined quarks and gluons. The QGP is believed to have existed a few microseconds after the Big Bang, and has been recreated in ultra-relativistic heavy ion collisions at both RHIC and LHC. Our targets hard probes of this dense matter, typically referring to high transverse momentum partons or jets (or electromagnetic emission) and their hadronic fragments. Due to the hard scale involved, these processes occur in the early stage of the collision, providing a window into the space-time evolution of the transient hot and dense nuclear medium. Both the initial production of hard probes and their subsequent interactions with the medium can be effectively treated using perturbative QCD, offering insights into the QGP's properties.

In additional to hot nuclear matter, we also focus on cold nuclear matter effects, which arise from parton multiple scatterings within cold nuclear matter. These scatterings can be incoherent or coherent, depending on the parton density, and are essential for understanding QCD dynamics in the nucleus, particularly in the nonlinear kinematic regime. At high parton densities, coherent multiple scatterings lead to the phenomenon of gluon saturation, where the growth of gluon density at small momentum fractions is tamed. This saturation is described within the framework of Color Glass Condensate (CGC), a critical tool for understanding QCD at high energies and exploring the behavior of fundamental particles in high-density environments. 

The research is closely connected to the experiments performed at RHIC, LHC, and the future EIC. 

Quantum Computing for Quantum Chromodynamics

The strong force, one of the four fundamental forces, is the most powerful among them. For instance, the interaction strength of the strong force, as described by Quantum Chromodynamics, is 100 times stronger than the electromagnetic force and a million times stronger than the weak force. This immense strength makes solving problems related to the strong interaction particularly challenging.

The fundamental structures of protons, neutrons, and atomic nuclei, as well as quantum phase transitions in QCD, involve quantum many-body systems of strongly interacting quarks and gluons. Accurately predicting the properties and dynamics of these systems requires vast classical computational resources - often exceeding the capabilities of even exascale computing.

As highlighted by Feynman and others, these quantum many-body systems may be more efficiently simulated using quantum computing, which scales polynomially with the system size. Although the application of quantum computing to QCD is still in its infancy, early models have demonstrated promising results. Our “Quantum Computing for QCD” (QC for QCD) initiative is in its early stages but has already made notable progress. The goal is to apply quantum computing to tackle QCD-related problems, aligning with the core mission of high-energy nuclear physics programs at Jefferson Lab, RHIC, LHC, and the future EIC.