EIC — Bring the Glue to Light

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!

3 The Low Energy View of Nuclear Matter nucleus = protons + neutrons nucleon  quark model quark model  QCD The High Energy View of Nuclear Matter The visible Universe is generated by quarks, but dominated by the dark glue! Remove factor 20 Exposing the high-energy (dark) side of the nuclei

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

6 EIC in Context

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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 I.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 Q 2 (HERA) II.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 EIC III.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 IV.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