The (2)H(e,e'p)n cross section at a momentum transfer of 3.5 (GeV/c)(2) was measured over a kinematical range that made it possible to study this reaction for a set of fixed missing momenta as a ...function of the neutron recoil angle θ(nq) and to extract missing momentum distributions for fixed values of θ(nq) up to 0.55 GeV/c. In the region of 35°≤θ(nq)≤45° recent calculations, which predict that final-state interactions are small, agree reasonably well with the experimental data. Therefore, these experimental reduced cross sections provide direct access to the high momentum component of the deuteron momentum distribution in exclusive deuteron electrodisintegration.
We have extracted QCD matrix elements from our data on doubly polarized inelastic scattering of electrons on nuclei. We find the higher twist matrix element d˜2, which arises strictly from ...quark-gluon interactions, to be unambiguously nonzero. The data also reveal an isospin dependence of higher twist effects if we assume that the Burkhardt-Cottingham sum rule is valid. The fundamental Bjorken sum rule obtained from the a0 matrix element is satisfied at our low momentum transfer.
Precision measurements of the relative analyzing powers of five electron beam polarimeters, based on Compton, Møller, and Mott scattering, have been performed using the CEBAF accelerator at the ...Thomas Jefferson National Accelerator Facility (Jefferson Laboratory). A Wien filter in the 100 keV beam line of the injector was used to vary the electron spin orientation exiting the injector. High statistical precision measurements of the scattering asymmetry as a function of the spin orientation were made with each polarimeter. Since each polarimeter receives beam with the same magnitude of polarization, these asymmetry measurements permit a high statistical precision comparison of the relative analyzing powers of the five polarimeters. This is the first time a precise comparison of the analyzing powers of Compton, Møller, and Mott scattering polarimeters has been made. Statistically significant disagreements among the values of the beam polarization calculated from the asymmetry measurements made with each polarimeter reveal either errors in the values of the analyzing power or failure to correctly include all systematic effects. The measurements reported here represent a first step toward understanding the systematic effects of these electron polarimeters. Such studies are necessary to realize high absolute accuracy (ca. 1%) electron polarization measurements, as required for some parity violation measurements planned at Jefferson Laboratory. Finally, a comparison of the value of the spin orientation exiting the injector that provides maximum longitudinal polarization in each experimental hall leads to an independent and very precise (better than 10−4 ) absolute measurement of the final electron beam energy.
Theoretical calculations predict the modification of properties of vector mesons, such as a shift in their masses and/or broadening of their widths in dense nuclear matter. These effects can be ...related to partial restoration of chiral symmetry at high density or temperature. Photoproduction of vector mesons off nuclei were performed at Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS). The data were taken with a beam of tagged photons with energies up to 4 GeV on various nuclear targets. The properties of the r vector mesons were investigated via their rare leptonic decay to e+e-. This decay channel is preferred over hadronic modes in order to eliminate final state interactions in the nuclear matter. The combinatorial background in the mass spectrum was removed by a self-normalizing mixed-event technique. The r meson mass distributions were extracted for each of the targets. Statistically significant results regarding medium modification of the rho meson in the nuclear medium rule out large medium effects. Transparency studies of the o and p vector mesons allows a determination of their widths in the medium.
The {sup 2}H(e,e{sup '}p)n cross section at a momentum transfer of 3.5 (GeV/c){sup 2} was measured over a kinematical range that made it possible to study this reaction for a set of fixed missing ...momenta as a function of the neutron recoil angle {theta}{sub nq} and to extract missing momentum distributions for fixed values of {theta}{sub nq} up to 0.55 GeV/c. In the region of 35 deg. {<=}{theta}{sub nq}{<=}45 deg. recent calculations, which predict that final-state interactions are small, agree reasonably well with the experimental data. Therefore, these experimental reduced cross sections provide direct access to the high momentum component of the deuteron momentum distribution in exclusive deuteron electrodisintegration.
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