ForewordThe study of the fundamental structure of nuclear matter is a central thrust of physics research in the United States. As indicated in Frontiers of Nuclear Science, the 2007 Nuclear Science Advisory Committee long range plan, consideration of a future Electron-Ion Collider (EIC) is a priority and will likely be a significant focus of discussion at the next long range plan. We are therefore pleased to have supported the ten week program in fall 2010 at the Institute of Nuclear Theory which examined at length the science case for the EIC. This program was a major effort; it attracted the maximum allowable attendance over ten weeks.This report summarizes the current understanding of the physics and articulates important open questions that can be addressed by an EIC. It converges towards a set of "golden" experiments that illustrate both the science reach and the technical demands on such a facility, and thereby establishes a firm ground from which to launch the next phase in preparation for the upcoming long range plan discussions. We thank all the participants in this productive program. In particular, we would like to acknowledge the leadership and dedication of the five co-organizers of the program who are also the co-editors of this report.David Kaplan, Director, National Institute for Nuclear Theory Hugh Montgomery, Director, Thomas Jefferson National Accelerator Facility Steven Vigdor, Associate Lab Director, Brookhaven National Laboratory iii Preface This volume is based on a ten-week program on "Gluons and the quark sea at high energies", which took place at the Institute for Nuclear Theory (INT) in Seattle from September 13 to November 19, 2010. The principal aim of the program was to develop and sharpen the science case for an Electron-Ion Collider (EIC), a facility that will be able to collide electrons and positrons with polarized protons and with light to heavy nuclei at high energies, offering unprecedented possibilities for in-depth studies of quantum chromodynamics. Guiding questions were• What are the crucial science issues?• How do they fit within the overall goals for nuclear physics?• Why can't they be addressed adequately at existing facilities?• Will they still be interesting in the 2020's, when a suitable facility might be realized?The program started with a five-day workshop on "Perturbative and Non-Perturbative Aspects of QCD at Collider Energies", which was followed by eight weeks of regular program and a concluding four-day workshop on "The Science Case for an EIC".More than 120 theorists and experimentalists took part in the program over ten weeks. It was only possible to smoothly accommodate such a large number of participants because of the extraordinary efforts of the INT staff, to whom we extend our warm thanks and appreciation. We thank the INT Director, David Kaplan, for his strong support of the program and for covering a significant portion of the costs for printing this volume. We gratefully acknowledge additional financial support provided by BNL and JLab.The program w...

The Jefferson Laboratory's superconducting radiofrequency (srf) Continuous Electron Beam Accelerator Facility (CEBAF) provides multi-GeV continuouswave (cw) beams for experiments at the nuclear and particle physics interface. CEBAF comprises two antiparallel linacs linked by nine recirculation beam lines for up to five passes. By the early 1990s, accelerator installation was proceeding in parallel with commissioning. By the mid-1990s, CEBAF was providing simultaneous beams at different but correlated energies up to 4 GeV to three experimental halls. By 2000, with srf development having raised the average cavity gradient to 7.5 MV/m, energies up to nearly 6 GeV were routine, at 1-150 µA for two halls and 1-100 nA for the other. Also routine are beams of >75% polarization. Physics results have led to new questions about the quark structure of nuclei, and therefore to user demand for a planned 12 GeV upgrade. CEBAF's enabling srf technology is also being applied in other projects.

We present a novel and quite general analysis of the interaction of a high-field chirped laser pulse and a relativistic electron, in which exquisite control of the spectral brilliance of the upshifted Thomson-scattered photon is shown to be possible. Normally, when Thomson scattering occurs at high field strengths, there is ponderomotive line broadening in the scattered radiation. This effect makes the bandwidth too large for some applications and reduces the spectral brilliance. We show that such broadening can be corrected and eliminated by suitable frequency modulation of the incident laser pulse. Further, we suggest a practical realization of this compensation idea in terms of a chirped-beam driven free electron laser oscillator configuration and show that significant compensation can occur, even with the imperfect matching to be expected in these conditions. PACS numbers: 29.20.Ej, 29.25.Bx, 29.27.Bd, 07.85.Fv Sources of electromagnetic radiation relying upon Thomson scattering are increasingly being applied in fundamental physics research [1], and compact acceleratorbased sources specifically designed for potential user facilities have been built [2]. One remarkable feature of the radiation emerging from such sources, compared to bremsstrahlung sources, is the narrowband nature of the radiation produced. For example, applications to Xray structure determination [3], dark-field imaging [4,5], phase contrast imaging [6], and computed tomography [7] have been demonstrated experimentally and take full advantage of the narrow bandwidth of the Thomson source.Given that narrow bandwidth is desired, it is important to know and understand the sources of bandwidth of the scattered radiation and the limitations imposed on the performance of Thomson sources. For applications where the normalized vector potential of the incident laser pulse is much less than one (the low-field regime), the line width of the radiation from a scattering event reproduces the line width of the incident laser pulse. Unfortunately, when the normalized vector potential increases, as is desired for stronger sources, a detuning red-shift arises during the scattering events that tends to spread out the spectrum [8][9][10]. Physically, the scattering electron slows down, by a varying amount, as the incident pulse is traversed.In a recent paper, Ghebregziabher, Shadwick, and Umstadter (GSU) observed that frequency modulation (FM), or "chirping", of the scattering laser pulse can compensate for such ponderomotive line broadening, and suggested a form for this modulation [11]. Motivated by their observation, we present the exact analytic solution for optimal FM, recovering the low-field linewidth even in the high-field regime. The narrowing of the scattered pulse is Fourier-limited only by the duration of the incident pulse.The essence of laser pulse chirping is analogous to free electron laser (FEL) undulator tapering [12][13][14][15][16]. In tapering, as deceleration occurs due to the FEL emission, the field strength is adjusted to preserve the...

General formulas for the far-field spectral distribution of photons Thomson scattered by a single electron have been obtained. Effects due to the pulsed nature of the laser beam are explicitly allowed, simultaneously with intensity high enough that harmonic generation is possible. For realistic pulsed photon beams, the spectrum of backscattered radiation is considerably broadened because of changes in the longitudinal velocity of the electrons during the pulse. Such ponderomotive broadening is especially pronounced at higher harmonics, eventually leading to a continuous emission spectrum.