# Research

The group has broad research interests across nuclear physics, with a particular speciality being applications of lattice QCD to contemporary problems.

Dudek's research interests lie principally in understanding the spectrum of excited hadrons within QCD. While the traditional picture of hadrons has mesons as $q\bar{q}$ bound-states and baryons as $qqq$, QCD in principle allows for a much richer spectrum, which might include states constructed from larger numbers of quarks, or hadrons featuring only glue (glueballs) or quarks and glue (hybrids).
Complicating matters is the fact that excited hadrons are unstable states, resonances, which can decay into lighter, stable hadrons, and the dynamics which binds quarks and gluons into hadrons is the same dynamics which controls their decay — both must be studied simultaneously.
Dudek is interested in application of lattice QCD to problems in hadron spectroscopy, and past calculations by Dudek and his collaborators appear to show, as well as the expected $q\bar{q}$-like mesons and $qqq$-like baryons, also the presence of hybrid mesons and baryons. The resonant nature of excited states can be studied through their appearance in scattering amplitudes, which can be extracted from lattice QCD calculations by utilizing the dependence of the lattice spectrum on the size of the 'box' defined by the lattice boundary. Dudek performs research on these topics within the hadspec collaboration.

Monahan's work uses lattice QCD to study the internal structure of hadrons, their weak interactions and in searches for new physics at the precision frontier. One strand of his research focuses on how quarks and gluons are arranged inside protons and neutrons, information that can be used at the LHC to reduce background uncertainties in searches for new particles.
A second strand focuses on determining the interactions of heavy hadrons, containing b quarks, with the weak nuclear force. These interactions are central to constraining the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix, which describes how quarks mix under the weak interaction. The CKM matrix is unitary in the Standard Model of particle physics, so any signs of non-unitarity could hint at the presence of unknown physics at high energies.
In addition, Monahan's research interests include the close interplay between the quantum field theory techniques used in lattice QCD and statistical physics, which describes the behavior of large systems of particles. In particular, Monahan studies thermal Casimir effects in fluids, which are the statistical analog of the famous electromagnetic Casimir force between two conducting plates.

Orginos's research focuses on understanding the physics of hadrons, whose dynamics is governed by the strong interactions. Quantum Chromodynamics (QCD), the theory of strong interactions, has a remarkably rich phenomenology. Because the interaction becomes strong at low energies, Lattice QCD is the only known way to compute rigorously the properties and interactions of hadrons directly from QCD. In recent years, substantial progress has been made in the field, providing us with the opportunity to compute many observables of central importance in subatomic physics. Using Lattice QCD Orginos is currently studying low energy hadronic phenomenology, including the structure and interactions of hadrons, weak interactions, and fundamental symmetries. In addition, he works on developing new computational techniques that make possible the study of phenomena currently inaccessible to available computational resources. Orginos's current research interests include hadron interactions, hadron structure, algorithms for lattice field theory and other topics in computational physics.

Emeritus Professor Carlson works on a variety of topics, mainly on the theme on using precision nuclear or particle physics to find discrepancies from standard-model physics, with a significant subinterest in optics and atomic physics, currently targeted on phenomena related to twisted photon states. Nuclear physics topics include two-photon physics to explain discrepancies between different ways of measuring the proton charge form factor, early-on-neglected corrections to the proton weak charge measurement that turned out to be larger than the anticipated experimental uncertainty, and corrections relevant to and possible beyond the standard model explanations of the proton radius puzzle. Regarding twisted photons, they are photon states of large intrinsic angular momentum, which can on atomic or nuclear targets induce quantum number changes impossible for plane wave photons. Far future applications include using energetic twisted photons to isolate high spin baryon or nuclear excited states. Currently we are successfully testing ideas by studying twisted photon phenomena in an atomic context.

The determination of the three-dimensional structure of hadrons in terms of the fundamental quark and gluon (or parton) degrees of freedom of QCD is one of the outstanding challenges of the Standard Model and a central mission of the Jefferson Lab science program. The Jefferson Lab Theory Center plays a leading role in the development of new formalisms and techniques to quantify this structure through various quantum correlation functions, such as parton distribution functions (PDFs), fragmentation functions (FFs), transverse momentum dependent distributions (TMDs), generalized parton distributions (GPDs), and multi-parton correlation functions. Opportunities for Ph.D. research in these areas are available at Jefferson Lab through Governor’s Distinguished CEBAF Professor Qiu and Adjunct Professors Melnitchouk and Richards.

In particular, the research of Qiu focuses on the theory and phenomenology of QCD to identify and develop factorization formalisms to match experimentally measured cross sections at Jefferson Lab and worldwide, as well as what can be calculated in lattice QCD, to the quantum correlation functions of quarks and gluons, and to extract these correlation functions from experimentally measured and lattice QCD calculated data.

The research of Melnitchouk, through the Jefferson Lab Angular Momentum (JAM) and CTEQ-JLab (CJ) collaborations, utilizes state-of-the-art analysis techniques, including Bayesian inference, Monte Carlo sampling, and machine learning, to extract the quantum correlation functions from experimental high-energy scattering data.