Measurement of the proton electric to magnetic form factor ratio from \vec ^1H(\vec e, 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 $Q^2$ 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 previous cross-section data on elastic electron-proton scattering in the same $Q^2$ region.Comment: 4 pages, 2 figures, submitted to PR

The BLAST Cherenkov detectors

We report on the design, construction, and operation of a large array of diffusely reflective aerogel Cherenkov detectors. They are part of the detector instrumentation of the Bates Large Acceptance Spectrometer Toroid (BLAST) at the MIT-Bates Linear Accelerator Center. The Cherenkov detectors are used for particle identification. They are able to discriminate between pions and electrons with momenta up to 700 MeV/c. (c) 2005 Elsevier B.V. All rights reserved

Precise Measurement of Deuteron Tensor Analyzing Powers with BLAST

We report a precision measurement of the deuteron tensor analyzing powers T[subscript 20] and T[subscript 21] at the MIT-Bates Linear Accelerator Center. Data were collected simultaneously over a momentum transfer range Q=2.15–4.50  fm[superscript -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[subscript C] and G[subscript Q] were separated with improved precision, and the location of the first node of G[subscript C] was confirmed at Q=4.19±0.05  fm[superscript -1]. The new data provide a strong constraint on theoretical models in a momentum transfer range covering the minimum of T[subscript 20] and the first node of G[subscript C].National Science Foundation (U.S.)United States. Dept. of Energ

Role of mesons in the electromagnetic form factors of the nucleon

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 Q2 [Q superscript 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 Q2 [Q superscript 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.United States. Dept. of Energy (Cooperative agreement DEFC02- 94ER40818)National Science Foundation (U.S.) (Grant no. PHY-0855584