Search Results (10 total)

Electroproduction of the ω meson was investigated in the ¹H(e,e^′p)ω reaction. The measurement was performed at a four-momentum transfer Q²≈0.5  GeV². Angular distributions of the virtual photon-proton center-of-momentum cross sections have been extracted over the full angular range. These distributions exhibit a strong enhancement over t-channel parity exchange processes in the backward direction. According to a newly developed electroproduction model, this enhancement provides significant evidence of resonance formation in the γ*p→ωp reaction channel.

We report the results from a systematic study of the quasielastic (e,e^′p) reaction on ¹²C,  ⁵⁶Fe, and ¹⁹⁷Au performed at Jefferson Lab. We have measured nuclear transparency and extracted spectral functions (corrected for radiation) over a Q² range of 0.64–3.25  (GeV∕c)² for all three nuclei. In addition, we have extracted separated longitudinal and transverse spectral functions at Q² of 0.64 and 1.8  (GeV∕c)² for these three nuclei (except for ¹⁹⁷Au at the higher Q²). The spectral functions are compared to a number of theoretical calculations. The measured spectral functions differ in detail but not in overall shape from most of the theoretical models. In all three targets the measured spectral functions show considerable excess transverse strength at Q²=0.64  (GeV∕c)², which is much reduced at 1.8  (GeV∕c)².

Inclusive electron scattering data are presented for ²H, C, Fe, and Au targets at an incident electron energy of 4.045 GeV for a range of momentum transfers from Q²=1 to 7 (GeV/c)². Data were taken at Jefferson Laboratory for low values of energy loss, corresponding to values of Bjorken x≳1. The structure functions do not show scaling in x in this range, where inelastic scattering is not expected to dominate the cross section. The data do show scaling, however, in the Nachtmann variable ξ. This scaling appears to be the result of Bloom- Gilman duality in the nucleon structure function combined with the Fermi motion of the nucleons in the nucleus. The resulting extension of scaling to larger values of ξ opens up the possibility of accessing nuclear structure functions in the high-x region at lower values of Q² than previously believed.

A newly obtained sample of inclusive electron-nucleon scattering data has been analyzed for precision tests of quark-hadron duality. The data are in the nucleon resonance region, and span the range 0.3<Q²<5.0 (GeV/c)². Duality is observed both in limited and extended regions around the prominent resonance enhancements. Higher twist contributions to the F₂ structure function are found to be small on average, even in the low Q² regime of ≈0.5 (GeV/c)². Using duality, an average scaling curve is obtained. In all cases, duality appears to be a nontrivial property of the nucleon structure function.

A newly obtained data sample of inclusive electron-nucleon scattering from both hydrogen and deuterium targets is analyzed. These JLab data span the nucleon resonance region up to four-momentum transfers of 5 (GeV/c)². The data are found to follow an average scaling curve. The inclusion of low-momentum transfer data yields a scaling curve resembling deep inelastic neutrino-nucleus scattering data, suggesting a sensitivity to valencelike structure only.

A separation of the longitudinal and transverse ¹²C(e,e^′p) cross sections in the quasifree region has been performed in parallel kinematics at Q² of 0.64 and 1.8 GeV² for initial proton momentum <80 MeV. The separated transverse and longitudinal spectral functions at Q²=0.64 GeV² show significant differences for missing energy between 25 and 60 MeV indicating a breakdown in the single nucleon knockout picture. The transverse spectral functions exhibit definite momentum transfer dependence.

The differential cross section for ²H(γ,d)π⁰ has been measured at deuteron center-of-mass angles of 90° and 136°. This work reports the first data for this reaction above a photon energy of 1 GeV, and permits a test of the apparent constituent counting rule and reduced nuclear amplitude behavior as observed in elastic ed scattering. Measurements were performed up to a photon energy of 4.0 GeV, and are in good agreement with previous lower energy measurements. Overall, the data are inconsistent with both constituent-counting rule and reduced nuclear amplitude predictions.

Inclusive electron scattering is measured with 4.045 GeV incident beam energy from C, Fe, and Au targets. The measured energy transfers and angles correspond to a kinematic range for Bjorken x>1 and momentum transfers from Q²  =  1–7 (GeV/c)². When analyzed in terms of the y-scaling function the data show for the first time an approach to scaling for values of the initial nucleon momenta significantly greater than the nuclear matter Fermi momentum (i.e., >0.3 GeV/c).

The first measurements of the differential cross section for the d(γ,p)n reaction up to 4.0 GeV were performed at the Continuous Electron Beam Accelerator Facility (CEBAF) at Thomas Jefferson Laboratory. We report the cross sections at the proton center-of-mass angles of 36°, 52°, 69°, and 89°. These results are in reasonable agreement with previous measurements at lower energy. The 89° and 69° data show constituent-counting-rule behavior up to 4.0 GeV photon energy. The 52° and 36° data disagree with the counting-rule behavior. The quantum chromodynamics (QCD) model of nuclear reactions involving reduced amplitudes disagrees with the present data.

The ( e,e^′p) reaction was studied on targets of C, Fe, and Au at momentum transfers squared Q² of 0.6, 1.3, 1.8, and 3.3 GeV² in a region of kinematics dominated by quasifree electron-proton scattering. Missing energy and missing momentum distributions are reasonably well described by plane wave impulse approximation calculations with Q² and A dependent corrections that measure the attenuation of the final state protons.