We report the measurement of the beam-vector and tensor asymmetries A_{ed}^{V} and A_{d}^{T} in quasielastic (e[over →],e^{'}p) electrodisintegration of the deuteron at the MIT-Bates Linear Accelerator Center up to missing momentum of 500  MeV/c. Data were collected simultaneously over a momentum transfer range 0.1<Q^{2}<0.5  (GeV/c)^{2} with the Bates Large Acceptance Spectrometer Toroid using an internal deuterium gas target polarized sequentially in both vector and tensor states. The data are compared with calculations. The beam-vector asymmetry A_{ed}^{V} is found to be directly sensitive to the D-wave component of the deuteron and has a zero crossing at a missing momentum of about 320  MeV/c, as predicted. The tensor asymmetry A_{d}^{T} at large missing momentum is found to be dominated by the influence of the tensor force in the neutron-proton final-state interaction. The new data provide a strong constraint on theoretical models.

We report a precision measurement of the deuteron tensor analyzing powers T(20) and T(21) at the MIT-Bates Linear Accelerator Center. Data were collected simultaneously over a momentum transfer range Q=2.15-4.50 fm(-1) with the Bates Large Acceptance Spectrometer Toroid using a highly polarized deuterium internal gas target. The data are in excellent agreement with calculations in a framework of effective field theory. The deuteron charge monopole and quadrupole form factors G(C) and G(Q) were separated with improved precision, and the location of the first node of G(C) was confirmed at Q=4.19±0.05 fm(-1). The new data provide a strong constraint on theoretical models in a momentum transfer range covering the minimum of T(20) and the first node of G(C).

The roles played by mesons in the electromagnetic form factors of the nucleon are explored using as a basis a model containing vector mesons with coupling to the continuum together with the asymptotic Q(2) behavior of perturbative QCD. Specifically, the vector dominance model (GKex) developed by E. L. Lomon is employed, as it is known to be very successful in representing the existing high-quality data published to date. An analysis is made of the experimental uncertainties present when the differences between the GKex model and the data are expanded in orthonormal basis functions. A main motivation for the present study is to provide insight into how the various ingredients in this model yield the measured behavior, including discussions of when dipole form factors are to be expected or not, of which mesons are the major contributors, for instance, at low Q(2) or large distances, and of what effects are predicted from coupling to the continuum. Such insights are first discussed in momentum space, followed by an analysis of how different and potentially useful information emerges when both the experimental and theoretical electric form factors are Fourier transformed to coordinate space. While these Fourier transforms should not be interpreted as "charge distributions," nevertheless the roles played by the various mesons, especially those which are dominant at large or small distance scales, can be explored via such experiment-theory comparisons.

The Bates large acceptance spectrometer toroid (BLAST) experiment was operated at the MIT-Bates Linear Accelerator Center from 2003 until 2005. The detector and experimental program were designed to study, in a systematic manner, the spin-dependent electromagnetic interaction in few-nucleon systems. As such the data will provide improved measurements for neutron, proton, and deuteron form factors. The data will also allow details of the reaction mechanism, such as the role of final state interactions, pion production, and resonances to be studied. The experiment used: a longitudinally polarized electron beam stored in the South Hall Storage Ring; a highly polarized, isotopically pure, internal gas target of hydrogen or deuterium provided by an atomic beam source: and a symmetric, general purpose detector based on a toroidal spectrometer with tracking. time-of-flight, Cherenkov, and neutron detectors. Details of the experiment and operation are presented. (C) 2009 Elsevier B.V. All rights reserved.

We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio G E n/G M n was extracted from the beam-target vector asymmetry A ed V at four-momentum transfers Q 2= 0.14, 0.20, 0.29, and 0.42 (GeV/c) 2.

We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio G(E)(n)/G(M)(n) was extracted from the beam-target vector asymmetry A(ed)(V) at four-momentum transfers Q(2) = 0.14, 0.20, 0.29, and 0.42 (GeV/c)(2).

We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio GEn/GMn was extracted from the beam-target vector asymmetry AedV at four-momentum transfers Q2=0.14, 0.20, 0.29, and 0.42 (GeV/c)2.

We report the first precision measurement of the proton electric to magnetic form factor ratio from spin-dependent elastic scattering of longitudinally polarized electrons from a polarized hydrogen internal gas target. The measurement was performed at the MIT-Bates South Hall Ring over a range of four-momentum transfer squared Q2 from 0.15 to 0.65 (GeV/c)(2). Significantly improved results on the proton electric and magnetic form factors are obtained in combination with existing cross-section data on elastic electron-proton scattering in the same Q2 region.

We report the first precision measurement of the proton electric to magnetic form factor ratio from spin-dependent elastic scattering of longitudinally polarized electrons from a polarized hydrogen internal gas target. The measurement was performed at the MIT-Bates South Hall Ring over a range of four-momentum transfer squared Q 2 from 0.15 to 0.65 (GeV/c) 2. Significantly improved results on the proton electric and magnetic form factors are obtained in combination with existing cross-section data on elastic electron-proton scattering in the same Q 2 region.

C. Crawford,1, 2 A. Sindile,3 T. Akdogan,1, 2 R. Alarcon,4 J. Althouse,5 W. Bertozzi,1, 2 E. Booth,6 T. Botto,1, 2 H.J. Bulten,7 J. Calarco,3 B. Clasie,1, 2 C. D’Andrea,5 A. deGrush,1, 2 K. Dow,1, 2 D. Dutta,8 M. Farkhondeh,1, 2 O. Filoti,3 W. Franklin,1, 2 H. Gao,1, 2, 8 E. Geis,4 S. Gilad,1, 2 A. Goodhue,5 W. Haeberli,9 D. Hasell,1, 2 W. Hersman,3 M. Holtrop,3 E. Ilhoff,1, 2 P. Karpius,3 J. Kelsey,1, 2 M. Kohl,1, 2 H. Kolster,1, 2 S. Krause,1, 2 T. Lee,3 A. Maschinot,1, 2 J. Matthews,1, 2 K. McIlhany,10 N. Meitanis,1, 2 R. Milner,1, 2 A. Mosser,10 J. Pavel,5 H.R. Poolman,7 J. Prince,4 J. Rapaport,11 R.P. Redwine,1, 2 J. Seely,1, 2 A. Shinozaki,1, 2 S. Širca,1, 2 T. Smith,5 S. Sobczynski,1, 2 B. Tonguc,4 C. Tschalaer,1, 2 E. Tsentalovich,1, 2 W. Turchinetz,1, 2 J.F.J. van den Brand,7 J. van der Laan,1, 2 T. Wise,9 Y. Xiao,1, 2 W. Xu,8 C. Zhang,1, 2 Z. Zhou,1, 2 V. Ziskin,1, 2 and T. Zwart1, 2 Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, MA 02139 MIT-Bates Linear Accelerator Laboratory, Middleton, MA 01949 University of New Hampshire, Durham, NH 03824 Arizona State University, Tempe, AZ 85287 Dartmouth College, Hanover, NH 03755 Boston University, Boston, MA 02215 Vrije Universitaet and NIKHEF, Amsterdam, The Netherlands Duke University, Durham, NC 27708-0305 University of Wisconsin, Madison, WI 53706 United States Naval Academy, Annapolis, MD 21402 Ohio University, Athens, OH 45701 (Dated: December 28, 2005)

The polarization dependence of Compton scattering in magnetized iron can be used to determine the polarization of an incident photon beam. This can in turn be related to the polarization of the electron beam which radiated the photons. It is difficult to calculate the analyzing power of these devices absolutely, however they are of great utility for rapid, relative measurements of electron beam polarization. These devices have been used at Bates as relative electron polarization monitors at 20 and 200 MeV. Efforts are now being made to use the device at 850 MeV as an online measure of the beam polarization in the South Hall Ring. A technique to calibrate these devices and build an affordable, absolute polarimeter is also being explored.

The MIT Bates 1 GeV electron scattering facility has recently completed a demanding set of parity violating experiments on the proton and the deuteron. These experiments required a polarized electron beam of unprecedented quality and high average currents. The facility has invested heavily in infrastructure for producing polarized beams and measuring beam polarization. This infrastructure includes a test beam set-up, a transmission polarimeter at 20 MeV, a laser back-scattering Compton polarimeter and a Siberian Snake. The polarized source group is also actively pursuing laser systems and photocathodes that could deliver high polarization, high peak current and moderate average current beams to meet the needs of the physics programs at Bates in the coming years.

A Compton polarimeter is being developed for the MIT/Bates South Hall Storage Ring. This polarimeter will be used to make measurements of the polarization of stored electron beams with energies below 1 GeV during internal target experiments.

The cross section for the reaction {sup 1}H({gamma},{pi}{sup 0}) has been measured using tagged photons in the threshold region (144.7{endash}169.3 MeV). The total cross section, augmented by angular distribution information, is used to deduce the {ital S}-wave multipole {ital E}{sub 0+}. Extrapolation to threshold yields {ital E}{sub 0+}=({minus}1.32{plus_minus}0.05{plus_minus}0.06){times}10{sup {minus}3}/{ital m}{sub {pi}}, in disagreement with earlier estimates. Suppression of {ital E}{sub 0+} near the {pi}{sup +} threshold is confirmed, in approximate agreement with recent calculations. {copyright} {ital 1996 The American Physical Society.}

An accurate calibration of the MIT-Bates electron beam energy has been achieved. The electron beam was injected into the MIT-Bates South Hall Ring and the spin-precession frequency, Ωs, was measured. From the spin-precession frequency the equilibrium energy of the ring was determined to be 370.3115±0.0021±0.0004 MeV, where the first error is statistical and the second is systematic. The energy of the beam delivered by the linac was determined to be 369.954±0.023±0.300 MeV. This provides a rigorous check on the accuracy of the facility's energy analyzing magnets. The first moment of the energy distribution was also measured. By observing the time constant of the spin diffusion with zero power in the South Hall Ring RF cavity, we obtained a value of σγγ = (3.7±0.5) × 10−4. We provide a lower limit to the polarization lifetime. At a beam energy of 370 MeV no measurable decrease in the polarization was observed up to 2 ms after injection.

Angular distributions for photon scattering from C-12 and He-4 have been measured using continuous wave bremsstrahlung from the Saskatchewan Accelerator Laboratory pulse stretcher ring. Data for carbon were taken at 158.8, 195.2, 197.2, 247.2, and 290.2 MeV end-point energies, and for helium were taken at an end-point energy of 158.8 MeV. A large NaI(Tl) gamma ray spectrometer with 1.7% resolution was used to detect the scattered photons at laboratory scattering angles, ranging from 20 degrees to 150 degrees. The excellent energy resolution of the NaI detector allowed a separation of elastic from inelastic photon scattering for the first time at these energies. The angular distributions for elastic scattering are in only fair agreement with delta-hole theory and theory based on the optical theorem at forward angles, and completely disagree with theory at backward angles. Measured cross sections for inelastic scattering leading to the 4.43 MeV state in carbon are small compared to the elastic scattering at forward angles, but are dominant at backward angles. This experiment is the first to separate elastic from inelastic photon scattering at these energies.

Impact parameter selected excited state populations were measured for [sup 36]Ar+[sup 197]Au reactions at [ital E]/[ital A]=35 MeV in order to better understand population inversions observed in a previous measurement of [sup 14]N+Ag reactions at [ital E]/[ital A]=35 MeV. The present impact parameter selected measurements revealed such population inversions to be most prominent in low multiplicity peripheral reactions. The excited state population for central collisions approach statistical model predictions for [ital T][approx]4 MeV.