The CEBAF II/ELIC Upgrade of CEBAF

Abstract

A strong physics case has been established for constructing an extremely high luminosity ({approx} 10{sup 38} cm{sup -2} sec{sup -1}), CEBAF-like accelerator with energies in the 20-30 GeV range. There have also been a series of studies investigating the scientific potential of an electron-light ion collider (ELIC) operating in the 20-65 GeV center-of-mass energy range. The facility at Jefferson Lab can be upgraded to provide either (or both) of these options in a straightforward manner. An energy upgrade of CEBAF to 25 GeV would support extensions of the CEBAF 12 GeV program to smaller x and higher Q{sup 2}, and, in particular, support a program of deeply virtual meson production that would permit the flavor separation of the Generalized Parton Distributions that characterize the nucleon's properties. A high-luminosity electron light ion collider (ELIC) in the center-of-mass energy range {radical}s of 20-65 GeV, would build on the physics insights obtained from the CEBAF 12 GeV upgrade, and expand on our understanding of the structure of the nucleon and nuclear binding. While questions remain on the details of the science program and on technical aspects of the facility design, we expect that the facility's research program will be absolutely central to themore » field of nuclear physics. In particular, such a facility will provide a unique tool to: (1) Complete our quantitative understanding of how quarks and gluons provide the binding and the spin of the nucleon; (2) Understand how quarks and gluons evolve into hadrons via the dynamics of confinement; and (3) Refine our understanding of how the nuclear binding arises from QCD. The April 2002 Long-Range Plan for the Next Decade, developed by the 2001-2002 Nuclear Sciences Advisory Committee (NSAC) Long Range Planning Process, noted that a 'ring-linac option where a linear electron beam is incident on a stored ion beam' is one of two classes of machine design for an electron-ion collider (the other is a ring-ring design). Since then, conceptual design studies for the facility have continued, and our latest results indicate that luminosities of up to 10{sup 35} cm{sup -2} sec{sup -1} are within reach, with a combination of a high-intensity, energy-recovered linac and a ring that has been optimized for this physics. A number of technical challenges remain, and several RD the design of an interaction region and detector that, taken together, support the combination of the very high luminosity and very high detector acceptance and resolution essential to carry out this physics program; and the demonstration of the feasibility of energy recovery at high current and high energy. For the latter, an early test on the GeV scale will occur at JLab in March, 2003. Given the level of R&D remaining to be done, the readiness of this project should be categorized as 'scientific and engineering issues still need to be resolved'.« less