Overview

This 7-week INT workshop was dedicated to the physics of the Electron Ion Collider (EIC), the world's first polarized electron-nucleon (ep) and electron-nucleus (eA) collider to be constructed in the USA following the 2015 NSAC recommendation as the highest priority long range plan. The primary goal of the EIC is to establish the precise multidimensional imaging of quarks and gluons inside nucleons and nuclei. This includes (i) understanding the spatial and momentum space structure of the nucleon through the studies of TMDs (transverse momentum dependent distributions), GPD (generalized parton distributions) and the Wigner distribution; (ii) determining the partonic origin of the nucleon spin; (iii) exploring a new quantum chromodynamics (QCD) frontier of ultradense gluon fields, with the potential to discover a new form of gluon matter predicted to be common to all nuclei.

The program brought together both theorists and experimentalists from Jefferson Lab (JLab), Brookhaven National Laboratory (BNL) along with the national and international nuclear physics communities to assess and advance the EIC physics. It summarized the progress in the field since the last INT workshop on EIC in 2010, outlined important new directions for theoretical research in the coming years and proposed new experimental measurements to be performed at the EIC.

Physics Questions Discussed

The key physics questions addressed by the program were as follows:

• How are the sea quarks and gluons, and their spins, distributed in space and momentum inside the nucleon?
  
  GPDs, TMDs and the Wigner distribution allow us to reveal the multi-dimensional nucleon structure in impact parameter and momentum space. The transverse spin polarization of the nucleon can be used as a crucial tool helping us understand nontrivial spin-orbital partonic correlations in the proton. Longitudinal spin structure of the nucleon will be definitely explored and the EIC will allow to constrain the gluon spin contribution to the spin of the nucleon.
  
  
• Where does the saturation of gluon densities set in?
  
  The large number of partons in a nucleus may result in strong gluon fields leading to the phenomenon of gluon saturation, known as the Color Glass Condensate. This universal regime of high-energy QCD is described by non-linear evolution equations. The program addressed the theoretical and phenomenological progress in our understanding of gluon saturation in ep, eA, along with proton-nucleus (pA) and nucleus-nucleus (AA) collisions.
  
  
• How does the nuclear environment affect the distribution of quarks and gluons and their interactions in nuclei?
  
  Nuclear PDFs, TMDs, and GPDs are interesting and important beyond small-x: the large-x structure of nuclei reflects important non-perturbative QCD dynamics in a cold nuclear matter environment, possibly providing essential information for our understanding of confinement. Cold nuclear matter can serve as a testing ground for the energy loss calculations describing propagation of an energetic quark or gluon in quark-gluon plasma (QGP) created in heavy ion collisions.