The inaugural QCD and Hadron Structure in the EIC Era workshop, sponsored by Argonne National Laboratory, will take place in downtown Chicago from November 30 to December 2, 2026.
Thirty-seven years ago, in 1989, the EMC experiment reported a striking result on the spin structure of the nucleon. What came to be known as the “proton spin crisis” challenged the simple picture of how the proton’s spin is built from its quark and gluon constituents and opened a new chapter in the study of nucleon structure. Over the following decades, understanding the spin and internal structure of the proton became one of the major driving forces of hadron and nuclear physics. It motivated a broad experimental and theoretical program, from the RHIC spin program to the 12 GeV upgrade at Jefferson Lab, and now to the Electron-Ion Collider. After nearly four decades, many of the questions raised by the EMC results have become much clearer, while some of the most fundamental ones remain with us.
A second major development came about thirty years ago with the introduction of generalized parton distributions, or GPDs. GPDs brought a new dimension to the study of nucleon structure. Parton distributions had taught us how quarks and gluons share the momentum of a fast-moving proton, while elastic form factors provided information about their spatial distributions. GPDs established a framework in which these two aspects could be correlated, allowing us to ask not only how much momentum a parton carries, but also where it is located inside the nucleon. Equally importantly, GPDs emerged in the context of understanding nucleon spin through their connection to the total angular momentum carried by quarks and gluons. They thus opened the door from the traditional one-dimensional description of the proton toward a multidimensional picture of its internal structure.
A third important direction has been the continuing effort to understand nucleon structure through field-theoretical models and nonperturbative pictures of QCD. Approaches based on instantons, as well as more recent developments inspired by AdS/CFT and gauge-gravity duality, have provided remarkably different yet complementary ways of thinking about how quarks and gluons organize themselves inside a proton. Such approaches go beyond simply parametrizing experimental data: they seek to identify the underlying dynamical mechanisms responsible for confinement, mass generation, spin structure, and the spatial organization of strongly interacting matter. Together with increasingly precise experiments and first-principles numerical calculations, these theoretical perspectives have helped turn the proton from a seemingly simple three-quark bound state into one of the richest laboratories for understanding nonperturbative quantum field theory.
These three developments—the long journey that began with the proton spin puzzle, the emergence of GPDs and multidimensional imaging, and the development of increasingly sophisticated field-theoretical descriptions of nucleon structure—provide much of the intellectual background for this conference. They also remind us how much the field has changed over the past several decades. We now have experimental capabilities, theoretical tools, and computational methods that could hardly have been imagined when the EMC result first appeared. At the same time, the central question remains remarkably simple: how does QCD build the proton that we observe?
The QCD and Hadron Structure in the EIC Era workshop will address this question by bringing together experts in theory, phenomenology, and experiment. This two-and-a-half-day workshop will be held in person and feature both 30-minute and 20-minute plenary talks.