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122 Chapter 10. Conclusion and Outlook
beyond the limits which were observed in the consistent approach (CEA). In fact,
we have found no evidence that the applicability of the optical potential model in the
eikonal approximation (OMEA) is restricted to a certain angular range.
At higher Q 2 [Q 2 > 1 (GeV/c) 2 ] nucleon-nucleus scattering becomes increasingly
diffractive, and descriptions of the reaction dynamics that rely on a potential
approach for the ejectile can no longer be justified. For that reason we have also
introduced a relativistic generalization of the Glauber approximation (RMSGA). In
such an approach the final state interactions in the nuclear medium are calculated
from pp and pn scattering data. The question arises whether the transition between
the low-energy regime, where optical potentials are used to calculate the scattering
states, and the high-energy regime, where the Glauber method is adopted, is
smooth.
To address this question, we have studied a large number of observables for the
12 C(e, e ′ p) and 16 O(e, e ′ p) reactions, and compared them with experimental results.
Although both methods treat final state interactions in a rather different manner,
it was shown that they produce comparable results for the differential cross sections,
structure functions and polarization observables. We consider the fact that both
methods produce similar spectroscopic strengths one of the major findings of this
work. In this comparison, special attention was paid to the R T L structure function.
It has been extensively discussed in literature that the contribution stemming
from the interference R T L structure function is very sensitive to slight changes in
the theoretical modelling of the reaction process, including the construction of the
scattering wave function. We have shown that the largest differences between the
optical model approach and the Glauber approach are indeed observed in the R T L
structure function. The left-right asymmetry A LT that is heavily influenced by the
R T L structure function, proved to be a very efficient tool to express these differences.
However, although both methods exhibit a very different p m dependence for large
missing momenta, they both reproduce the experimental trend, thereby illustrating
the necessity of including final state interactions at high missing momenta.
A major concern in any relativistic approach are the uncertainties that arise from
the choice of the electromagnetic electron-proton coupling. We have quantified the
effects of the ambiguities on the observables by comparing results obtained with a
number of current operators and methods to restore current conservation. In line
with other investigations we have found that the off-shell ambiguities grow with
increasing missing momenta. Further, it was demonstrated that a modification
of the longitudinal component of the vector current according to J z → (ω/q)J 0 ,
which restores current conservation, produces the smallest off-shell ambiguities in
the calculated results. Also, the current operator CC2 was put forward as the
most favorable choice for the electron-proton coupling as calculations employing this
operator proved to be rather insensitive to the chosen gauge restoration scheme.
A key issue in the considerations of off-shell ambiguities was the Q 2 dependence
of the induced uncertainties on the reaction observables. It is often claimed that