Session EQ: Mini-Symposium: Electromagnetic FF of N*'s II

Ground and excited nucleon structure within continuum QCD approaches

The task of mapping and explaining the spectrum of nucleon and delta resonances, and the structure of these states in terms of quarks and gluons is a longstanding challenge in hadron physics, which is likely to persist for another decade or more. We review the progress made in this topic using a Schwinger functional method which combines Dyson-Schwinger equations with covariant bound-state equations for conventional hadrons, namely Bethe-Salpeter and Faddeev equations. This framework provides a non-perturbative, Poincaré-covariant continuum formulation of Quantum Chromodynamics (QCD) which is able to extract novel insight on baryon properties since the physics at the hadron level is directly related with the underlying quark-gluon substructure, via convolution of Green functions. Since the approach provides access to all momentum scales, it is particularly suited to study N* elastic and transition form factors as well as their associated generalized parton distributions; therefore, examples of the calculation of this kind of observables shall be discussed.   

3D Ground Nucleon Structure from SIDIS

Nucleon is the basic building block of the visible universe, yet our knowledge about its structure at large space-time scales, where the perturbative QCD is not applicable, is still rudimentary. The Wigner distribution is a five-dimensional quantum phase space distribution that provides a unified framework describing the nucleon structure in terms of the parton distributions inside the nucleon. Integrating the Wigner distribution over its intrinsic transverse coordinate leads to the transverse-momentum-dependent (TMD) parton distribution function. TMD depicts a three-dimensional imaging of the nucleon, and plays an important role in understanding its spin structure. This three-dimensional distribution is experimentally accessible via the Drell-Yan process and the Semi-Inclusive Deep Inelastic (SIDIS) process. In this talk, I will discuss about the SoLID SIDIS program at JLab, and its projections on the 3D imaging of the nucleon will be presented.   

Nucleon Elastic Form Factors from the 6 GeV and 12 GeV eras at CEBAF

The electromagnetic form factors (EMFFs) of the nucleon, measured in elastic lepton-nucleon scattering, are of central importance to hadronic physics, and continue to be a highly active area of experimental and theoretical investigation, both at low and high energies and momentum transfers. They serve as a first benchmark for testing state-of-the-art theoretical models of the nucleon and \textit{ab initio} predictions of nucleon ground- and excited-state properties and dynamical behavior in lattice QCD. Through their model-independent connections to moments of Generalized Parton Distributions, the form factors can also be used to construct realistic images of the nucleon charge and magnetization densities in impact parameter space. Finally, precise knowledge of the ground state EMFFs of the nucleon over a wide range of $Q^2$ is required for the interpretation of a diverse array of experiments across nuclear, particle, and hadronic physics. In this talk I will review the experimental status of nucleon electromagnetic form factors, with an emphasis on the legacy of the 6 GeV era of CEBAF, and the near-future program of precision high-$Q^2$ form factor measurements in the 12 GeV era, including the upcoming Super BigBite Spectrometer (SBS) program, slated to begin in 2021.   

Regge approaches for semi-inclusive electron scattering

I will discuss the role of Regge theory in studies of hadron structure and spectroscopy.   

Measurements of the Inclusive Electron Scattering off Protons with CLAS12

Electron scattering data off protons from the CLAS12 detector in Hall B at Jefferson Laboratory have become available and cover a wide kinematic range in W up to 4 GeV and Q$^{\mathrm{2}}$ up to 10 GeV$^{\mathrm{2}}$, offering new opportunities to explore inclusive, semi-inclusive, and fully exclusive reactions. A study that aims to extract the inclusive electroproduction cross sections from the CLAS12 data collected at a beam energy of 10.6 GeV from an unpolarized liquid-hydrogen target is now in progress and preliminary results will be presented. Because of the large acceptance of CLAS12, these data offer a unique opportunity to measure inclusive cross sections at W from the N\textunderscore threshold to W from 2.0 GeV to 3.0 GeV within any given Q$^{\mathrm{2}}$-bin. This unique W-coverage at fixed Q2-values is of particular importance for the extension of our knowledge on the nucleon parton distribution function~from the data on F2 structure function in the resonance region by employing the existing CLAS results on the \textunderscore $_{\mathrm{v}}$pN* electroexcitation amplitudes. These studies also offer valuable input for the exploration of quark-hadron duality.   

Exploring nucleon PDFs and quark-hadron duality from inclusive electron scattering data in the resonance region

We present our study of proton structure functions in view of the new CLAS12 experiments, which are to study inclusive electron scattering at a wide $Q^2$ range and with a broad coverage over Bjorken variable $x$ ($N^*$ region and above) at any given $Q^2$. So far, CLAS experiments have achieved major advances in the extraction of electrocouplings of most nucleon resonances in the mass range up to 1.8 GeV, showing consistency between the results from different meson electroproduction channels. We evaluate the contributions from the resonances to inclusive electron scattering $F_2$ and $F_L$ functions using the electrocoupling data as input, for the first time. Similarly, the contributions to the polarized structure functions $g_1$ and $g_2$ can be readily obtained as well. These studies are important for a future precise extraction of proton PDFs in the resonance region and for tests on quark-hadron duality.   

Advances in the PDF description from QCD

Over the last 30 years, significant work has been devoted to understand the structure of the nucleon in terms of its quarks and gluon degrees of freedom using QCD factorization theorems. In this talk I will give an overview of the subject and comment on existing challenges that can be addressed at the Jefferson Lab 12 GeV and the future EIC.