Session 1WA: Nuclear Physics at the Energy-luminosity Frontier: From JLab 12 GeV to an Electron-Ion Collider

Opening: Nuclear Physics at the Energy-luminosity Frontier

Electron scattering is an essential tool for exploring Quantum Chromodynamics (QCD) and the short-range structure of hadrons and nuclei. Over the next two decades two new experimental facilities are expected to extend the combined energy-luminosity frontier: the Jefferson Lab 12 GeV Upgrade, and a future Electron-Ion Collider. Together they can provide qualitatively new insight into the 3-dimensional quark and gluon structure of the nucleon, the dynamics of color fields in nuclei, and the emergence of hadrons from the QCD color charge. This introduction briefly explains the context and plan of the workshop.   

Three-dimensional nucleon structure: Spin, spatial imaging, orbital motion

Recent theoretical advances in Quantum Chromodynamics make it possible to visualize hadrons as extended systems in relativistic space-time and describe their spin structure, spatial shape, and internal motion in terms of the basic quark and gluon degrees of freedom. Mapping these structures will require a dedicated experimental effort over the next two decades. The Jefferson Lab 12 GeV Upgrade will probe the valence quark component of the nucleon with unprecedented accuracy. A future high-luminosity Electron-Ion Collider (EIC) could open up the region of sea quarks and gluons and definitively determine their role in nucleon structure. In this talk I summarize our theoretical understanding and illustrate the impact of the future facilities on nucleon structure in QCD.   

Probing the QCD origin of Nuclear Forces at JLab12 \& EIC

We review several directions of studies of QCD origin of nuclear forces at EIC. The main emphasis is given to the studies that will be initiated within the 12 GeV fixed target program of the Jefferson Lab and will be continued at EIC energies and collider kinematics. Such studies include the probing QCD content of the NN repulsive core, the role of the gluons in the formation of nuclear forces at short distances, hidden-color component of the nuclear wave function, the dynamics of the quark - hadron transition and hadronization in deep-inelastic semi-inclusive processes involving nuclear targets. We demonstrate how the collider kinematics provide an unprecedented advantage in tagging high momentum components of the nuclear wave function at momenta that are currently considered inaccessible. Utilizing these kinematics we present the theoretical estimates of the several key processes and emphasize their discovery power in probing different aspects of the QCD dynamics of the nuclear forces at short distances.   

The Emergence of Hadrons from QCD Color

The propagation of colored quarks through strongly interacting systems, and their subsequent evolution into color-singlet hadrons, are phenomena that showcase unique facets of Quantum Chromodynamics (QCD). Medium-stimulated gluon bremsstrahlung, a fundamental QCD process, induces broadening of the transverse momentum of the parton, and creates partonic energy loss manifesting itself in experimental observables that are accessible in high energy interactions in hot and cold systems. The formation of hadrons, which is the dynamical enforcement of the QCD confinement principle, is very poorly understood on the basis of fundamental theory, although detailed models such as the Lund string model or cluster hadronization models can generally be tuned to capture the main features of hadronic final states. With the advent of the technical capability to study hadronic final states with good particle identification and at high luminosity, a new opportunity has appeared. Study of the characteristics of parton propagation and hadron formation as they unfold within atomic nuclei are now being used to understand the coherence and spatial features of these processes and to refine new experimental tools that will be used in future experiments. Fixed-target data on nuclei with lepton and hadron beams, and collider experiments involving nuclei, all make essential contact with these topics and they elucidate different aspects of these same themes. In this talk, a survey of the most relevant recent data and its potential interpretation will be followed by descriptions of feasible experiments at an electron-ion collider, in the context of existing measurements as well as the experiments performed following the upgrade of Jefferson Lab to 12 GeV.   

Electron Ion Collider: The next QCD frontier

While QCD is certainly the correct theory of Strong Interactions, our understanding of it remains far from complete. The precise role gluons and sea quarks play in QCD in terms of the internal structure and dynamics of hadrons and nuclei is not known. The Relativistic Heavy Ion Collider (RHIC) with its high-energy polarized proton and heavy ion beams, and the 12 GeV upgraded CEBAF with the fixed target experiments in Hall A, B, C and D at the Jefferson Lab will explore and advance many aspects of QCD studies in the valence quark region the next few years. A high-energy, high-luminosity polarized electron-ion collider (EIC) will be needed to explore the gluon dominated regions in the nuclei. Its high luminosity will be critical to study (a) the three dimensional position and momentum structure of the nucleons including its spin and (b) precision electro-weak physics resulting in sensitivity to phenomena beyond the Standard Model. Two proposals for the EIC are being considered in the US: one each at BNL and at Jefferson Laboratory. Preliminary ideas are being developed in China for a polarized electron-proton/light ion collider. I will review these proposals of the EIC, and comment on the physics opportunities they present to the nuclear science communities around the world in the next decade.   

eRHIC: The BNL vision of an electron-ion collider

An electron-ion collider (EIC) will be the ``QCD Laboratory'' of the future. Combining high luminosity and polarization with the flexibility to collide electrons with ions ranging from protons to uranium nuclei will enable experimental investigations of the structure of the quarks sea and gluon ocean in nucleons and nuclei with unprecedented precision and kinematic leverage. The EIC will also enable femtoscopic studies of the dynamics of QCD processes from the perturbative to the confinement regime. I will describe how RHIC can be converted into an EIC serving a world-wide community of scientists interested in exploring the many remaining mysteries of how quarks and gluons conspire to build nucleons and nuclei.   

EIC: The View from Jefferson Lab

The prospect of an EIC for advancing our knowledge of QCD, nucleon structure, and nuclear physics has been of increasing interest around the world during the last few years. The perspective for realization of an EIC in the US will be examined from the viewpoint of Jefferson Lab, its user community, and the US nuclear physics community.