E. Geis

-Measurement of the proton's electric to magnetic form factor ratio from 1H(over -->)(e(over -->),e'p).

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.

The Charge Form Factor of the Neutron at Low Momentum Transfer from the H-2-polarized (e-polarized, e-prime n) p Reaction

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.

The Charge Form Factor of the Neutron at Low Momentum Transfer from the

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.

^{2}\vec{\rm H}(\vec{\rm e},{\rm e}'{\rm n}){\rm p}

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.

Reaction

Measurement of the charge form factor of the neutron GnE presents a sensitive test of nucleon models and QCD-inspired theories. In particular, the pion cloud is expected to play a dominant role in the low-momentum transfer region of GnE . At the MIT-Bates Linear Accelerator Center, GnE has been measured by means of quasielastic scattering of polarized electrons from vector-polarized deuterium, 2~ H(~e,e’n). The experiment used the longitudinally polarized stored electron beam of the MIT-Bates South Hall Ring along with an isotopically pure, highly vector-polarized internal atomic deuterium target provided by an atomic beam source. The measurements have been carried out with the symmetric Bates Large Acceptance Spectrometer Toroid (BLAST) with enhanced neutron detection capability. From the beam-target double polarization asymmetry A ed with the target spin oriented perpendicular to the momentum transfer the form factor G E is extracted over a range of four-momentum transfer Q between 0.12 and 0.70 (GeV/c) with minimized model dependencies.

Role of mesons in the electromagnetic form factors of the nucleon

Measurement of the charge form factor of the neutron GEn presents a sensitive test of nucleon models and QCD‐inspired theories. In particular, the pion cloud is expected to play a dominant role in the low‐momentum transfer region of GEn. At the MIT‐Bates Linear Accelerator Center, GEn has been measured by means of (e,e’) quasielastic scattering of polarized electrons from vector‐polarized deuterium. The experiment used the longitudinally polarized stored electron beam of the MIT‐Bates South Hall Ring along with an isotopically pure, highly vector‐polarized internal atomic deuterium target provided by an atomic beam source. The measurements have been carried out with the symmetric Bates Large Acceptance Spectrometer Toroid (BLAST) with enhanced neutron detection capability. From the beam‐target double polarization asymmetry with the target spin oriented perpendicular to the momentum transfer the form factor GEn is extracted over a range of four‐momentum transfer Q2 between 0.12 and 0.70 (GeV/c)2 with minim...

The Charge Form Factor of the Neutron at Low Q2

Measurement of the neutron’s electric form factor, GE , by means of quasi-elastic electron scattering from polarized deuterium with polarized beam and target, 2 H( e, e′n)p, is in progress at the South Hall Ring of the MIT-Bates Linear Accelerator Center using the Bates Large Acceptance Spectrometer Toroid (BLAST). The spin-perpendicular vector-polarized beam-target asymmetry, Aed provides the ratio, GE/G n M over a range of momentum transfer Q 2 between 0.12 and 0.80 (GeV/c)2 . Preliminary results will be presented.