High-momentum Protons and the
(e,e'p) Cross Section
The presence of high-momentum nucleons in the nuclear ground state
remains an issue of great interest. The possible experimental
demonstration of such high-momentum components has been explored in a
theoretical calculation of the cross section for the (e,e'p)
reaction. The spectral function of
16O was obtained earlier in
publ.59 by solving the Dyson equation in the finite nucleus using
a realistic nucleon-nucleon (NN) interaction. A meaningful
theoretical determination of the coincidence cross section for the
(e,e'p) reaction involves both the nucleon spectral function and a
realistic description of the wave function of the ultimately detected
proton inside the nucleus. In order to proceed to a more complete
theoretical treatment of the coincidence cross section and to
establish the possible detectability of removal processes involving
protons with high initial momentum, our group, in collaboration with
the Pavia group, has used the theoretical spectral functions obtained
in publ.53 and
publ.59 to determine the coincidence cross section for the
(e,e'p) reaction on 16O. The
results of this collaboration have been published in
publ.71 and publ.72. At low missing
energy the removal of protons from
p3/2 quasihole states has been
studied. The comparison of the missing momentum dependence of these
transitions with experimental data from NIKHEF
ref.1 and Mainz ref.2 is very favorable.
The slight difference between theory and experiment at high missing
momenta can at most account for a very tiny fraction of the
single-particle (sp) strength. This strength is predicted to be
present at these momenta publ.53,
publ.59 based on information of the
momentum distribution. A comparison for the
p3/2 quasihole state with the
results of ref.3 using the Argonne v14 NN
interaction ref.4 suggests that the Green's
function result yields a slightly better description of the momentum
dependence of the cross section. While the shape of the cross section
is nicely described by these new results, the associated
spectroscopic factors are overestimated substantially. A substantial
fraction of this discrepancy can be ascribed to the influence of
long-range correlations publ.69. A
nonnegligible discrepancy remains, however, since a correct treatment
of the center-of-mass motion cannot explain the remaining difference
ref.5. Our results
publ.71, publ.72 clearly support the
notion that the presence of high-momentum components in the nuclear
ground state can only be explored by considering high missing
energies in the (e,e'p) reaction. Although other processes may
contribute at these energies, our results demonstrate that detectable
cross sections can be expected, indicating the presence of
high-momentum nucleons in the nucleus. On the other hand, we obtain
negligible cross sections for high-momentum nucleons at low missing
energy, further supporting the results obtained in
publ.53, publ.59. Experimental work at JLab has recently confirmed the presence of high-momentum components at high missing energy ref.6.
M. Leuschner et al., Phys. Rev. C49, 955
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