Image Credit: This work was a collaborative effort of Rolf Ent (Physicist, Jefferson Lab) and Richard Milner (Physicist, MIT). Proton animations by James LaPlante (Animator, Sputnik Animation). Edited by Alexander Higginbottom (MIT Video Productions). Film consultants Christopher Boebel and Joe McMaster (Film Producers, MIT).

Event ID: INT-25-1

OVERVIEW

The Electron-Ion Collider (EIC) to be constructed at Brookhaven National Laboratory over the coming decade will be the most powerful tool thus far for exploring the inner structure of matter and the forces that hold matter together. It will provide images of protons and nuclei at their deepest level, and with unprecedented precision. EIC construction and planning for the project detector ePIC are now well underway. For the EIC to succeed, advances in the precision of the theoretical description of the relevant ep and eA reactions will be vital. The goal of our program is to identify the outstanding problems and the progress to be made, to facilitate work toward advancing EIC theory, and to forge new collaborations and alliances that will tackle the challenges. We expect that the program will also serve to generate additional new ideas for further measurements at the EIC.

To achieve these goals, we plan to engage the community at large and bring together the leading theorists and experimentalists interested in QCD precision studies at the EIC. In this way, work on addressing the challenges for theory will go hand in hand with a careful assessment of the experimental plans and realities.

Key topics at our program will be: discussion of NNLO techniques and preparations of high-order perturbative-QCD calculations; novel state-of-the-art resummation techniques and phenomenology for the EIC; development of high-order frameworks for analysis of nucleon structure and its tomography; comparisons of phenomenological and lattice determinations; jet production studies for the EIC; identification of signature observables for saturated gluons; assessment of the importance of AI techniques for EIC studies.

PROGRAM FORMAT

Each program week has a particular physics topic as will be described below. We expect to have around 20 participants in residence at INT in each week. We plan to have about two organized sessions per day. We are very glad to have assembled a group of additional co-organizers who will work with us on setting up and running the program:

Miguel Arratia (UC Riverside, US)
Daniel de Florian (Univ. of San Martin, Argentina)
Thomas Gehrmann (Univ. of Zürich, Switzerland)
Zhong-Bo Kang (UC Los Angeles, US)

For each program week, at least two of our full organizational team will be present and lead the discussions. We plan to have about two organized sessions per day: one will be in the morning and will typically bring together all participants of the week. This session can have up to three 30-45 minute presentations, along with ample time for discussion. Another session will take place in the afternoon. It will usually be more informal and involve perhaps only a subset of the participants who are interested in a specific topic. There can also be two or more of such sessions in parallel. The program will provide sufficient time for the participants to collaborate and work.

The structure of the program will be as follows:

Week 1 (May 12-16; de Florian, Gehrmann): Precision theory for hard scattering at the EIC, factorization and resummation

Precision will play a fundamental role in the analysis of the data generated by the EIC and it will be necessary that the most advanced theoretical calculations are available. A similar situation was observed at the LHC, where next-to-next-to leading order (NNLO) perturbative QCD calculations became the state-of-the-art for all benchmark processes, allowing predictions at a precision level of a few percent. Each of the precision observables at the EIC poses novel types of challenges to precision theory, and the combination of experts from different subfields we hope to assemble for our program will provide a forum to identify these challenges and to devise strategies to address them.

Week 2 (May 19-23; Fatemi, Lin, Vogelsang): Parton distributions and the interplay of EIC and LHC: Lattice QCD meets phenomenology

The EIC will enhance all the information about parton distributions obtained from previous facilities. We will assess how EIC, JLab, RHIC and LHC data could complement each other in global precision analysis of parton densities. We also expect collaboration among the leaders of the most advanced analyses of the spin structure of the nucleon towards comparisons of analysis techniques and codes. On EIC time scales, first-principles calculations of the x-dependence of PDFs on the lattice will have matured and will provide unique complementary insights that are perhaps not accessible in experiment. Discussion of the new opportunities provided by the lattice is therefore an important component of the program we envisage, including steps towards a framework for inclusion of lattice data in global PDF analyses. Comparison of various methods proposed for the computation of the x-dependence of PDFs on the lattice and perturbative matching calculations will also be focal points.

Week 3 (May 26-30; Kang, Vogelsang): Small-x physics in the EIC era

At high energies gluon densities in hadrons grow quickly, resulting in a novel high-density regime of nuclear matter controlled by non-linear QCD effects. Hadrons in this small-x regime are characterized by saturated, classical gluon fields, rather than the usual partonic description. Because these highdensity effects are enhanced in nuclei, the EIC presents an ideal opportunity to search for signals of this novel regime of QCD. The experimental discovery and in-depth quantification of gluon saturation will require a new era of theoretical developments aiming to push the precision of the CGC framework to the standards of collinear perturbative QCD. We plan to address the critical measurements for the discovery of a gluon saturated state: structure functions, exclusive reactions, and semi-inclusive reactions. Our program will connect the theoretical studies to the EIC machine and detector capabilities. An ideal outcome would be to establish a set of “smoking-gun” signatures of saturated gluons at the EIC.

Week 4 (June 9-13; Arratia, Lin): Artificial intelligence and enhanced design

The EIC community has embraced Artificial intelligence (AI) algorithms and techniques and is incorporating them into all aspects of design and development, ranging from accelerator and detector optimization, to streaming data acquisition and the advancement of simulation and reconstruction tools. The upcoming two years will be an intense period of EIC detector design, and the INT program is well timed to bring together experts to discuss novel AI techniques employed in this process. Simulation and reconstruction tools will develop in parallel as they are an integral part of the design evaluation. Our program will take stock of the landscape of AI techniques being used in the EIC design process and define new areas of opportunity as the community transitions from the design to the construction and commissioning phase.

Week 5 (June 16-20; Arratia, Fatemi, Kang): Jets and semi-inclusive reactions: Nucleon and nuclear tomography

Imaging of nucleons and nuclei is a key focus of the EIC physics program and is realized by measurements of TMDs and GPDs, which both may be viewed as descendants of Wigner functions. GPDs provide access to the spatial structure of hadrons and may be probed in novel off-forward scattering processes. We will address the recent progress and future prospects, which includes the QCD analysis of off-forward reactions, lattice calculations of GPDs, and the use of advanced mathematical methods and AI/ML for GPD extraction in global analyses.

TMDs transcend virtually all aspects of our program: (1) their study and phenomenology involve a deep understanding of factorization issues; (2) scale evolution of TMDs is a direct counterpart to transverse-momentum resummation in perturbative QCD; (3) when the transverse momentum of the observed hadron increases, TMDs need to be “matched” to fixed-order collinear-factorized cross sections; (4) at small x, TMDs must be similarly “matched” onto the semi-classical degrees of freedom of the CGC; (5) the recent progress on the lattice mentioned earlier also allows for computations of TMDs. For each of these topics just mentioned, open theoretical issues remain which we will discuss at our program.

Semi-inclusive observables involving produced hadrons or jets are key for TMD studies at the EIC, but equally so for the study of the formation of QCD final states, a topic that is so central to our knowledge and understanding of QCD. Jet studies at the EIC, especially when compared with precision jet physics at the LHC, have the promise to provide new clues on the hadronization of QCD partons exiting from a hard collision. A number of new ideas were also presented in recent years regarding the interplay between the production of jets and heavy quarks. These include the flavor-tagging of jets, the use of charmed jets as a probe for strangeness in both unpolarized and polarized scattering and the study of lepton-jet correlations for nuclear tomography at the EIC. We intend to address all these exciting applications of EIC jet physics at our program.

We note that the separate workshop 25-93W, “Bridging Theory and Experiment at the Electron-Ion Collider” organized by A. Bacchetta, W. Cosyn, F. Ringer, A. Stasto will take place between weeks 3 and 4 of our program. See link on https://www.int.washington.edu/programs-and-workshops for further information.