An Assessment of U.S.-Based Electron-Ion Collider Science

Understanding of protons and neutrons, or "nucleons"?the building blocks of atomic nuclei?has advanced dramatically, both theoretically and experimentally, in the past half century. A central goal of modern nuclear physics is to understand the structure of the proton and neutron directly from the dynamics of their quarks and gluons governed by the theory of their interactions, quantum chromodynamics (QCD), and how nuclear interactions between protons and neutrons emerge from these dynamics. With deeper understanding of the quark-gluon structure of matter, scientists are poised to reach a deeper picture of these building blocks, and atomic nuclei themselves, as collective many-body systems with new emergent behavior.The development of a U.S. domestic electron-ion collider (EIC) facility has the potential to answer questions that are central to completing an understanding of atoms and integral to the agenda of nuclear physics today. This study assesses the merits and significance of the science that could be addressed by an EIC, and its importance to nuclear physics in particular and to the physical sciences in general. It evaluates the significance of the science that would be enabled by the construction of an EIC, its benefits to U.S. leadership in nuclear physics, and the benefits to other fields of science of a U.S.-based EIC.Table of ContentsFront MatterSummary1 Introduction2 The Scientific Case for an Electron-Ion Collider3 Role of an EIC Within the Context of Nuclear Physics in theUnited States and Internationally4 Accelerator Science, Technology, and Detectors Needed for aU.S.-Based Electron-Ion Collider5 Comparison of a U.S.-Based Electron-Ion Collider to Current andFuture Facilities6 Impact of an Electron-Ion Collider on Other Fields7 Conclusions and FindingsAppendix A Statement of TaskAppendix B Committee and Staff Biographical InformationAppendix C Acronyms