Deuteron electrodisintegration cross sections near 180$\sp\circ$ have been measured in the break-up threshold region for the squared four-momentum transfer $Q\sp2$ range 1.21 to 2.77 (GeV/c)$\sp2$. These measurements constitute part of Experiment NE4, performed at the Standford Linear Accelerator Center during the years 1985 and 1986. The data have relatively coarse energy resolution, 12 to 20 MeV in relative neutron-proton energy $E\sb{np}$, and predictions are examined using two methods: Various non-relativistic predictions are folded with Monte-Carlo determined resolution functions, and a model-dependent resolution-unfolding procedure was employed, yielding results averaged over $E\sb{np}$ from 0 to 10 MeV. Systematic errors arose predominantly from a $\pm$0.25% uncertainty in the scattered electron energy $E\sp1$. These results are compared with theoretical predictions averaged over similar ranges of $E\sb{np}$. The comparisons indicate that meson exchange currents (MEC) have a strong influence on the measured cross section up to $E\sb{np}$ = 20 MeV. However, the calculations have great sensitivity to the choice of form factor for the meson-nucleon coupling. Evidence for a possible change in slope of the cross section has been obtained for the first time. This feature is predicted to arise from interference effects between the IA, $\pi$ and $\rho$ exchange, $\Delta$ resonance interactions, and, perhaps, a quark exchange effect. No existing model lies in complete agreement with the data over the entire measured range of $Q\sp2$. The inelastic structure functions $W\sb1$($E\sb{np}$, $Q\sp2$), and $W\sb2$($E\sb{np}$, $Q\sp2$) are obtained from the present results and previous forward angle data. The deduced ratios, $W\sb1$/$W\sb2$ $\approx$ 1 for $E\sb{np}$ $>$ 50 MeV, but decrease as $E\sb{np}$ $\to$ 0, in accord with earlier results at lower $Q\sp2$. All non-relativistic predictions are in agreement above $E\sb{np}$ = 50 MeV, indicating that the IA interaction dominates in this region. In contrast, no prediction is in good agreement at small $E\sb{np}$. The present results expose the inadequacies of non-relativistic treatments of MEC, and should stimulate the development of relativistic theories employing nucleons with MEC, and more formally sound quark-inspired models.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-7916 |
| Date | 01 January 1990 |
| Creators | Frodyma, Marc B |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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