Role of mesons in the electromagnetic form factors of the nucleon

Prof. Gao's research focuses on understanding the structure of the nucleon in terms of quark and gluon degrees of freedom of Quantum Chromodynamics (QCD), search for QCD exotics, and fundamental symmetry studies at low energy to search for new physics beyond the Standard Model of electroweak interactions. Most recently, her group's studies of the structure of the nucleon have been focusing on a precision measurement of the proton (see her group's 2019 Nature paper on this topic) and deuteron charge radii to elucidate on the proton and the deuteron charge radius puzzles, and on imaging the three-dimensional structure of the nucleon in momentum space through the extraction of transverse momentum dependent parton distribution functions (TMDs), employing polarized semi-inclusive deep inelastic scattering processes. The nucleon tomography provided by TMDs will uncover the rich QCD dynamics, and provide quantitative information about the quark orbital angular momentum contribution to the proton spin. TMDs will also provide information on fundamental quantities such as the tensor charge of the nucleon, a quantity not only important for testing lattice QCD predictions, but also important for searches of new physics beyond the Standard Model together with the next generation of nucleon electric dipole moment experiments. Her group is playing leading roles in the Solenoidal Large Intensity Device (SoLID) project at Jefferson Lab, a high profile program which will make major impact on TMD physics, proton mass puzzle through precision measurement of J/psi production near threshold, and search for new physics beyond the Standard Model using parity-violating deep inelastic scattering. Most of her work utilizes the novel experimental technique of scattering polarized electrons or photons from polarized gas targets. Her group has built a number of state-of-the-art polarized gas targets including H/D internal gas target and a high-pressure polarized ³He target for photon experiments using the High Intensity Gamma Source (HIGS) facility at the Duke Free Electron Laser Laboratory (DFELL). Her research is being carried out mostly at the Thomas Jefferson National Accelerator Facility (JLab) in Newport News, Virginia, and the HIGS facility at DFELL.