A workshop on The Next Generation Gamma-Ray Sources sponsored by the Office of Nuclear Physics at the Department of Energy, was held November 17--19, 2016 in Bethesda, Maryland. The goals of the workshop were to identify basic and applied research opportunities at the frontiers of nuclear physics that would be made possible by the beam capabilities of an advanced laser Compton beam facility. To anchor the scientific vision to realistically achievable beam specifications using proven technologies, the workshop brought together experts in the fields of electron accelerators, lasers, and optics to examine the technical options for achieving the beam specifications required by the most compelling parts of the proposed research programs. An international assembly of participants included current and prospective $\gamma$-ray beam users, accelerator and light-source physicists, and federal agency program managers. Sessions were organized to foster interactions between the beam users and facility developers, allowing for information sharing and mutual feedback between the two groups. The workshop findings and recommendations are summarized in this whitepaper.

Quadrupole amplitudes in the $\gamma^{*}N\to\Delta$ transition are associated with the issue of nucleon deformation. A search for these small amplitudes has been the focus of a series of measurements undertaken at Bates/MIT by the OOPS collaboration. We report on results from H$(e,e^\prime p)\pi^0$ data obtained at $Q^2= 0.070$ (GeV/c)$^2$ and invariant mass of W=1155 MeV using the out-of-plane detection technique with the OOPS spectrometers. The $\sigma_{LT}$ and $\sigma_{T}+\epsilon\cdot$ $\sigma_{L}$ response functions were isolated. These results, along with those of previous measurements at $W$=1172 MeV and $Q^2= 0.127$ (GeV/c)$^2$, aim in elucidating the interplay between resonant and non resonant amplitudes.

We report on the design and performance of compact detector packages currently installed in the four magnetic out-of-plane spectrometers for electron scattering experiments at the MIT-Bates Linear Accelerator Center. The detector packages have been designed to meet the mechanical requirements arising from out-of-plane particle detection. They offer good trajectory and momentum reconstruction, particle identification and time-of-flight measurements for electrons, pions, protons, and deuterons with large momentum bites and in broad kinematical ranges and high luminosities. The detectors have so far been used with great success in out-of-plane measurements of 12C(e→,e′p), 2H(e→,e′p), virtual Compton scattering below pion threshold and in studies of the N→Δ transition in both exclusive reaction channels 1H(e→,e′p)π0 and 1H(e→,e′π+)n.

Measurements of the (2)H((-->)e,e(')p)n reaction were performed with the out-of-plane magnetic spectrometers (OOPS) at the MIT-Bates Linear Accelerator. The longitudinal-transverse, f(LT) and f(')(LT), and the transverse-transverse, f(TT), interference responses at a missing momentum of 210 MeV/c were simultaneously extracted in the dip region at Q2 = 0.15 (GeV/c)(2). In comparison to models of deuteron electrodisintegration, the data clearly reveal strong effects of relativity and final-state interactions and the importance of two-body meson-exchange currents and isobar configurations. We demonstrate that such effects can be disentangled by extracting these responses using the novel out-of-plane technique.

We have measured the coincidence d(e→,e′p) reaction in quasielastic scattering, detecting the proton in a noncoplanar geometry. The electron helicity asymmetry Ae and the imaginary part of the longitudinal-transverse interference structure function f′LT have been determined at a four-momentum transfer Q2=3.3 fm−2. The results are compared with theoretical calculations which use realistic potentials for the NN interaction.Received 1 September 1994DOI:https://doi.org/10.1103/PhysRevC.51.3479©1995 American Physical Society

We report the results of measurements of the properties of a prototype out-of-plane magnetic spectrometer (OOPS). This spectrometer is one of four identical modules which, together with a support structure, comprise the OOPS cluster. The performance of the spectrometer was found to closely match its design characteristics.

We have measured a new electron scattering observable, the ''fifth'' structure function, f01', which is the imaginary part of the transverse-longitudinal interference response. Its observation requires a longitudinally polarized beam and coincident, out-of-plane particle detection. f01' arises from interference between reaction channels and provides an additional means for their disentanglement. In the quasielastic C-12(e over arrow pointing right, e'p) measurements reported here, f01' is driven by the interference of the direct knockout and rescattering amplitudes.

The H3 and He3 charge and magnetic form factors have been extracted from cross-section measurements in the region 0.3≲Q≲2.9 fm−1. The measurements have random uncertainties of about 2% and systematic uncertainties of about 2% for H3 and 1.5% for He3. The small systematic uncertainties allow accurate determination of the isoscalar and isovector trinucleon form factors. The isoscalar charge and isovector magnetic form factors are in reasonable agreement with current theoretical models, whereas the isovector charge and isoscalar magnetic form factors show significant deviations from the models.Received 27 May 1987DOI:https://doi.org/10.1103/PhysRevLett.59.1537©1987 American Physical Society