Gluons dominate QCD • QCD is the fundamental theory that describes structure and interactions in nuclear matter. • Without gluons there are no protons, no neutrons, and no atomic nuclei • Facts: • The essential features of QCD (e.g. asymptotic freedom, chiral symmetry breaking, and color confinement) are all driven by the gluons! • Unique aspect of QCD is the self interaction of the gluons • 98% of mass of the visible universe arises from glue • Half of the nucleon momentum is carried by gluons • However, gluons are dark: they do not interact directly with light high-energy collider!
Exposing the high-energy (dark) side of the nuclei The High Energy View of Nuclear Matter The visible Universe is generated by quarks, but dominated by the dark glue! • The Low Energy View of Nuclear Matter • nucleus = protons + neutrons • nucleon quark model • quark model QCD Remove factor 20
Explore the new QCD frontier: strong color fields in nuclei Precisely image the sea-quarks and gluons in the nucleon
EIC science has evolved from new insights and technical accomplishments over the last decade • ~1996 development of GPDs • ~1999 high-power energy recovery linac technology • ~2000 universal properties of strongly interacting glue • ~2000 emergence of transverse-spin phenomenon • ~2001 world’s first high energy polarized proton collider • ~2003 RHIC sees tantalizing hints of saturation • ~2006 electron cooling for high-energy beams
Why HERA did not do EIC physics? • eA physics: • Up to Ca beams considered • Low luminosity (1000 compared to EIC) • Would have needed ~$100M to upgrade the source to have more ions, but still the low luminosity • Polarized e-p physics • HERA-p ring is not planar • No. of Siberian snake magnets required to polarize beam estimated to be 6-8: Not enough straight sections for Siberian snakes and not enough space in the tunnel for their cryogenics • Technically difficult • DESY was a HEP laboratory focused on the high energy frontier.
Mapping and understanding the role of glue in the nucleon: • The fundamental properties of the nucleon are dominated by gluons! • Without the gluons, the nucleon mass would be just 10 MeV (98% of mass of the visible universe arises from glue) • Half of the nucleon momentum is carried by gluons. • We expect significant contribution to the proton spin from glue • A full exploration of gluons in the nucleon: gluon-tomography at EIC! • Mapping out the gluon helicity contribution to the nucleon spin at the highest energy. • Mapping out the space and momentum distributions of the gluons through novel hard exclusive processes.
Draft Sidebar: The Glue at the Heart of Matter • Gluons are majority “silent partners” in ordinary matter • A. Gluon self-interactions responsible for novel features of QCD B. Not apparent in quantum #’s, but dominate mass of visible universe C. Apparent untamed growth in gluon density at low x, high Q2 (HERA) • Do gluons play an important role in proton spin? • A. “Missing spin” problem B. Launch of RHIC spin program + early constraints on gluon pol’n C. Direct sensitivity via photon-gluon fusion processes D. Ultimate determination by scaling violations in DIS @ EIC • What QCD giveth, QCD taketh away • A. Competition between gluon splitting and recombination saturation B. Do all protons and nuclei look the same when viewed at high energy? C. Search for universal saturated gluonic matter at EIC • Gluons made manifest? • A. Are there excited states of hadrons where gluons contribute directly to exotic quantum #’s? B. Photo-excitation as the way to excite gluonic vibrations C. GLUEx experiment at upgraded CEBAF