Y. Hatta
Kyoto University

Y. Kovchegov
The Ohio State University

C. Marquet
CPHT - Ecole Polytechnique

A. Prokudin
Penn State University Berks

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Kimberlee Choe
(206) 685-3509

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INT Program INT-18-3

Probing Nucleons and Nuclei in High Energy Collisions

October 1 - November 16, 2018


This 7-week INT program is 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 United States. The 2015 NSAC Long Range Plan recommended EIC as the "highest priority for new facility construction following the completion of FRIB". The primary goal of the EIC is to establish precise multi-dimensional 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 parton distributions), GPD (generalized parton distributions) and the Wigner distribution; (ii) determining the partonic origin of the nucleon spin; (iii) exploring the new quantum chromodynamics (QCD) frontier of ultra-strong gluon fields, with the potential to seal the discovery of a new form of dense gluon matter predicted to exist in all nuclei and nucleons at small Bjorken x - the parton saturation.

The program will bring 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 will summarize the progress in the field since the last INT workshop on EIC in 2010, outline important new directions for theoretical research in the coming years, and propose new experimental measurements to be performed at the EIC.

Physics Questions

The key physics questions to be addressed by the program are 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 would address the theoretical and phenomenological progress in our understanding of gluon saturation in ep, eA, along with the proton-proton (pp), 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 energetic quarks and gluons in quark-gluon plasma (QGP) created in heavy ion collisions.

Program Structure

Except for the symposium week, each day of the program will usually consist of about two seminars in the morning with free discussions and informal seminars in the afternoon. The participants are encouraged to stay for several weeks in order to facilitate cross-disciplinary discussions and research. The topics organized week-by-week are as follows:

Week 1 (October 1-5) : Generalized parton distributions
Conveners: Tanja Horn, Andreas Metz, Christian Weiss

The first week will focus on various aspects of GPDs: theory, phenomenology, lattice QCD computations, models. The recent progress and efforts towards the EIC will be discussed.

Week 2 (October 8-12) : Transverse spin and TMDs
Conveners: Harut Avakian, Alessandro Bacchetta, Daniel Boer, Zhongbo Kang

The focus will be shifted to the physics of TMDs such as TMD factorization and evolution, phenomenological implementations, relation to jet physics, and lattice results.

Week 3 (October 15-19) : Longitudinal spin
Conveners: Elke Aschenauer, Keh-Fei Liu, Cedric Lorce, Marco Stratmann

A week devoted to the longitudinal spin structure of the proton including the unpolarized/ polarized PDFs, spin sum rules, the orbital angular momentum of the proton (OAM) and lattice results.

Week 4 (October 22-26) : Symposium week
A five-day symposium will be held during the central week, covering all the major topics related to the EIC.

Weeks 5 & 6 (October 29-November 9) : eA collisions
Conveners: Giovanni Chirilli, Charles Hyde, Anna Stasto, Thomas Ullrich, Bowen Xiao

These two weeks will focus on the physics of electron-ion collisions. Topics such as nuclear PDF/TMD/GPD, non-linear small-x evolution equations, diffraction, particle production and correlations will be discussed.

Week 7 (November 12-16) : pA and AA collisions
Conveners: Adrian Dimitru, Francois Gelis, Tuomas Lappi, Yacine Mehtar-Tani

The final week will be devoted to studying implications of what we would learn in eA collisions at EIC for our understanding of pA and heavy ion collisions at RHIC and LHC (and vice versa).