The Electron Ion Collider
To understand the fundamental structure of matter has been an elusive goal of physicists through
the ages. With the development of the Standard Model in the 1970's, there finally existed a theoretical
framework with the possibility to explain strongly interacting matter in terms of fundamental, irreducible
constituents. The strong interaction and its manifestations in atomic nuclei, i.e. in the dynamical structure
and behavior of nucleons, mesons, and nuclei, are at the core of nuclear physics research. The Electron-
Ion Collider (EIC) is proposed as an essential tool for research into the fundamental structure of matter.
To build upon the insights gained from present research, EIC will be necessary by the end of this decade.
Some of the crucial questions to be addressed by EIC include:
What is the structure of hadrons in terms of their quark and gluon constituents?
How do quarks and gluons evolve into hadrons?
How do quarks and gluons reveal themselves in the structure of atomic nuclei?
Can nuclei be used to study partonic matter under extreme conditions?
EIC is a next-generation facility for electromagnetic and hadronic physics with a CM energy in
the range of about 30 to 100 GeV with a luminosity of at least 1033 A cm-2s-1. The collider has its origins
in two sources: an effort focussed on hadron structure involving the proton and light nuclei, known as
EPIC; an effort to use the existing polarized proton and nuclear beams of the RHIC collider with an
electron beam to study partonic effects in nuclei, known as eRHIC. Workshops at IUCF, BNL, Yale and
MIT over the last year have culminated in one non-site specific initiative, EIC, to develop the scientific
case and machine options.
MIT-Bates role in EIC
For the last year, MIT-Bates has played a leadership role in EIC. With the support of the MIT
Dean of Science, a feasibility study of the ring-ring machine option was carried out in collaboration with
physicists from the Budker Institute for Nuclear Physics, Novosibirsk, Russia. In this design (see page 2-
23 of MIT-Bates Linear Accelerator Report 2000), 7 GeV electrons collide with 32 GeV protons in a 1.4 km circumference ring configuration.
Polarization of the electrons is an important question. One approach is to use wigglers to drive the
Sokolov-Ternov self-polarization mechanism. With this scheme, electrons can be injected at relatively
low energy, removing the necessity for a high energy, expensive linac, ramped to 7 GeV and self-
polarized, as at HERA. It is highly desirable to pursue this avenue and the Bates SHR can be an
important test-bench to experimentally study self-polarization at low energies.
In addition, physics simulations and detector design are underway involving physicists at Bates
and in the MIT Medium Energy Group. Of particular interest are spin-dependent charm production to
study the spin structure of the proton and exclusive process such as DVCS to access generalized parton
distributions. A major area of study is to produce an optimized detector design which will be consistent
with the high luminosity constraints in the interaction region.
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