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 quality and intensity of gamma rays at the High Intensity gamma-ray Source are shown to make nuclear resonance fluorescence studies possible at a new level of precision and efficiency. First experiments have been carried out using an intense (10(7) gamma/s) beam of 100% linearly polarized, nearly monoenergetic, gamma rays on the semimagic nucleus (138)Ba. Negative parity quantum numbers have been assigned to 18 dipole excitations of (138)Ba between 5.5 MeV and 6.5 MeV from azimuthal gamma-intensity asymmetries.

We report first results from our effort to couple a high resolution photoemission electron microscope (PEEM) to the OK-4 ultraviolet free electron laser at Duke University (OK-4/Duke UV FEL). The OK-4/Duke UV FEL is a high intensity source of tunable monochromatic photons in the 3–10 eV energy range. This tunability is unique and allows us to operate near the photoemission threshold of any samples and thus maximize sample contrast while keeping chromatic berrations in the PEEM minimal. We have recorded first images from a variety of samples using spontaneous radiation from the OK-4/ Duke UV FEL in the photon energy range of 4.0–6.5 eV. Due to different photothreshold emission from different sample areas, emission from these areas could be turned on (or off) selectively. We have also observed relative intensity reversal with changes in photon energy which are interpreted as density-of-state contrast. Usable image quality has been achieved, even though the output power of the FEL in spontaneous emission mode was several orders of magnitude lower than the anticipated full laser power. The PEEM has achieved a spatial resolution of 12 nm.

The photon analyzing power for the photodisintegration of the deuteron was measured for seven gamma-ray energies between 2.39 and 4.05 MeV using the linearly polarized gamma-ray beam of the High-Intensity Gamma-ray Source at the Duke Free-Electron Laser Laboratory. The data provide a stringent test of theoretical calculations for the inverse reaction, the neutron-proton radiative capture reaction at energies important for Big-Bang Nucleosynthesis. Our data are in excellent agreement with potential model and effective field theory calculations. Therefore, the uncertainty in the baryon density ΩBh 2 obtained from Big-Bang Nucleosynthesis can be reduced at least by 20%. 24.70.+s, 27.10.+h, 21.45.+v Big-Bang Nucleosynthesis (BBN) is an observational cornerstone of the hot Big-Bang (BB) cosmology. According to [1] the neutron(n)-proton(p) capture reaction p(n, γ)d with a deuteron (d) and a 2.225 MeV γ ray in the exit channel is of special interest, because the BB abundance of deuterium provides direct information on the baryon density in the early universe at times between about 0.01 and 200 seconds after the BB. Knowing accurately the n-p capture cross section in the energy range from 25 to 200 keV in the center-of-mass (c.m.) system and using the experimental value for the primeval deuterium number density (D/H) p [2, 3], would allow for an accurate determination of the baryon density Ω B h 2 (h is the Hubble constant in units of 100 km/s/Mpc). From Ω B h 2 one can predict the abundances of the three light elements 3 He, 4 He, and 7 Li. According to [1], the 10% uncertainty in the deuterium-inferred baryon density Ω B h 2 = 0.019 ± 0.002 comes in almost equal parts from the (D/H) measurements and theoretical uncertainties in predicting the deuterium abundance. For the latter, the knowledge of the n-p capture cross section is of crucial importance. Unfortunately, there is a near-complete lack of data at energies relevant to BBN. Aside from thermal energies, data exist only at n-p c.m. energies of 275 keV and above. As a consequence, the ENDF-B/VI [4] evaluation has been used [1] in the BBN energy range. This evaluation is normalized to the high-precision thermal n-p capture cross-section measurements. The 5% uncertainty that is assigned in this approach contributes a significant fraction to the uncertainty in the baryon density and consequently in the abundances of the light elements produced in BBN.Very recently, with the precision results from WMAP (Wilkinson Microwave Anisotropy Probe) for the Cosmic Microwave Background (CMB) and its anisotropies an independent and even more accurate result became available: Ω B h 2 = 0.0224 ± 0.0009 [5,6]. The comparison of the baryon density predictions from BBN and the CMB is a fundamental test of BB cosmology [7]. Any deviation points to either unknown systematics or the need for new physics. Therefore, it is of crucial importance to reduce the uncertainty in Ω B h 2 obtained from BBN. As stated above, 50% of the uncertainty is due to the uncertainty in the n-p capture cr...

Radiotherapy utilizes photons for treating cancer. Historically these photons have been produced by the bremsstrahlung process. In this paper we introduce Compton backscattering as an alternate method of photon production for cancer treatment. Compton backscattering is a well-established method to produce high-energy photons (gamma rays) for nuclear physics experiments. Compton backscattering involves the collision of a low-energy (eV) photon with a high-energy (hundreds of MeV) electron. It is shown that the photons scattered in the direction opposite to the direction of the initial photon (backscattered) will have the energy desired for photon beam therapy. The output of Compton backscattering is a high-energy photon beam (gamma-ray beam), which is well collimated and has minimal low-energy components. Such gamma beams may be used for conventional high-energy photon treatments, production of radionuclides, and generation of positrons and neutrons. The theoretical basis for this process is reviewed and Monte Carlo calculations of dose profiles for peak energies of 7, 15, and 30 MeV are presented. The potential advantages of the Compton process and its future role in radiotherapy will be discussed.