An EIC slams electrons into protons or heavier ions to investigate the quarks and gluons inside the nucleons. A collider with high energy and luminosity—a measure of the rate at which particle collisions occur—would have the fine resolution needed to answer some of the big-picture questions cited by the committee. Those include elucidating the origin of the mass and spin of nucleons, learning how gluons hold nuclei together, and determining whether emergent forms of matter made of dense gluons exist.
Beyond nuclear science, an EIC would benefit astrophysics, high-energy physics, accelerator physics, and theoretical and computational modeling, the committee writes. Further, it is the only high-energy accelerator (excluding light sources) being considered for construction in the nation, and building it would help to maintain US expertise in accelerator and collider science. “An EIC would be a unique facility in the world and would maintain US leadership in nuclear physics,” the report states. Although there is no existing EIC, China is also considering building one.
While this facility has the word "collider" attached to it, this is not a high-energy physics facility nor will it be funded out of the high-energy physics directorate of the DOE and NSF. It will be a nuclear physics facility, just like RHIC, CEBAF, and the upcoming FRIB.
Now, if only the politicians in Washington can be convinced of the need to build such a thing... y'know, make America "great" again, even though we no longer have any high-energy physics collider on US soil.