57 research outputs found
Systematic study of Coulomb distortion effects in exclusive (e,e'p) reactions
A technique to deal with Coulomb electron distortions in the analysis of
(e,e'p) reactions is presented. Thereby, no approximations are made. The
suggested technique relies on a partial-wave expansion of the electron wave
functions and a multipole decomposition of the electron and nuclear current in
momentum space. In that way, we succeed in keeping the computational times
within reasonable limits. This theoretical framework is used to calculate the
quasielastic (e,e'p) reduced cross sections for proton knockout from the
valence shells in O, Ca, Zr and Pb. The
final-state interaction of the ejected proton with the residual nucleus is
treated within an optical potential model. The role of electron distortion on
the extracted spectroscopic factors is discussed.Comment: 45 pages, 10 encapsulated postscript figures, Revtex, uses epsfig.sty
and fancybox.sty, to be published in Physical Review
Analysis of Meson Exchange and Isobar Currents in (e,e'p) Reactions from O-16
An analysis of the effects of meson exchange and isobar currents in exclusive
(e,e'p) processes from O-16 under quasi-free kinematics is presented. A model
that has probed its feasibility for inclusive quasi-elastic (e,e') processes is
considered. Sensitivity to final state interactions between the outgoing proton
and the residual nucleus is discussed by comparing the results obtained with
phenomenological optical potentials and a continuum nuclear shell-model
calculation. The contribution of the meson-exchange and isobar currents to the
response functions is evaluated and compared to previous calculations, which
differ notably from our results. These two-body contributions cannot solve the
puzzle of the simultaneous description of the different responses
experimentally separated. Copyright 1999 by The American Physical SocietyComment: 5 pages, plus 3 PS figures. To be published in Phys. Rev. C Updated
figure
Overlap functions in correlation methods and quasifree nucleon knockout from O
The cross sections of the () and () reactions on O
are calculated, for the transitions to the ground state and the first
excited state of the residual nucleus, using single-particle overlap
functions obtained on the basis of one-body density matrices within different
correlation methods. The electron-induced one-nucleon knockout reaction is
treated within a nonrelativistic DWIA framework. The theoretical treatment of
the () reaction includes both contributions of the direct knockout
mechanism and of meson-exchange currents. The results are sensitive to details
of the different overlap functions. The consistent analysis of the reaction
cross sections and the comparison with the experimental data make it possible
to study the nucleon--nucleon correlation effects.Comment: 26 pages, LaTeX, 5 Postscript figures, submitted to PR
Meson exchange currents in electromagnetic one-nucleon emission
The role of meson exchange currents (MEC) in electron- and photon-induced
one-nucleon emission processes is studied in a nonrelativistic model including
correlations and final state interactions. The nuclear current is the sum of a
one-body and of a two-body part. The two-body current includes pion seagull,
pion-in-flight and the isobar current contributions. Numerical results are
presented for the exclusive 16O(e,e'p)15N and 16O(\gamma,p)15N reactions. MEC
effects are in general rather small in (e,e'p), while in (\gamma,p) they are
always large and important to obtain a consistent description of (e,e'p) and
(\gamma,p) data, with the same spectroscopic factors. The calculated (\gamma,p)
cross sections are sensitive to short-range correlations at high values of the
recoil momentum, where MEC effects are larger and overwhelm the contribution of
correlations.Comment: 9 pages, 6 figure
Meson Exchange Currents in (e,e'p) recoil polarization observables
A study of the effects of meson-exchange currents and isobar configurations
in reactions is presented. We use a distorted wave
impulse approximation (DWIA) model where final-state interactions are treated
through a phenomenological optical potential. The model includes relativistic
corrections in the kinematics and in the electromagnetic one- and two-body
currents. The full set of polarized response functions is analyzed, as well as
the transferred polarization asymmetry. Results are presented for proton
knock-out from closed-shell nuclei, for moderate to high momentum transfer.Comment: 44 pages, 18 figures. Added physical arguments explaining the
dominance of OB over MEC, and a summary of differences with previous MEC
calculations. To be published in PR
Measurement of Nuclear Transparency for the A(e,e' pi^+) Reaction
We have measured the nuclear transparency of the A(e,e' pi^+) process in
^{2}H,^{12}C, ^{27}Al, ^{63}Cu and ^{197}Au targets. These measurements were
performed at the Jefferson Laboratory over a four momentum transfer squared
range Q^2 = 1.1 - 4.7 (GeV/c)^2. The nuclear transparency was extracted as the
super-ratio of from data to a model of
pion-electroproduction from nuclei without pi-N final state interactions. The
Q^2 and atomic number dependence of the nuclear transparency both show
deviations from traditional nuclear physics expectations, and are consistent
with calculations that include the quantum chromodynamical phenomenon of color
transparency.Comment: 5 pages, 3 figs Changes to figure 2 and 3 (error band updated and
theory curves updated
Restoration of Overlap Functions and Spectroscopic Factors in Nuclei
An asymptotic restoration procedure is applied for analyzing bound--state
overlap functions, separation energies and single--nucleon spectroscopic
factors by means of a model one--body density matrix emerging from the Jastrow
correlation method in its lowest order approximation for and
nuclei . Comparison is made with available experimental data and mean--field
and natural orbital representation results.Comment: 5 pages, RevTeX style, to be published in Physical Review
Measurement of the 12C(e,e'p)11B Two-Body Breakup Reaction at High Missing Momentum Values
The five-fold differential cross section for the 12C(e,e'p)11B reaction was
determined over a missing momentum range of 200-400 MeV/c, in a kinematics
regime with Bjorken x > 1 and Q2 = 2.0 (GeV/c)2. A comparison of the results
and theoretical models and previous lower missing momentum data is shown. The
theoretical calculations agree well with the data up to a missing momentum
value of 325 MeV/c and then diverge for larger missing momenta. The extracted
distorted momentum distribution is shown to be consistent with previous data
and extends the range of available data up to 400 MeV/c.Comment: 12 pages, 1 table and 3 figures for submission to Journal Physics
Relativistic mean field approximation to the analysis of 16O(e,e'p)15N data at |Q^2|\leq 0.4 (GeV/c)^2
We use the relativistic distorted wave impulse approximation to analyze data
on 16O(e,e'p)15N at |Q^2|\leq 0.4 (GeV/c)^2 that were obtained by different
groups and seemed controversial. Results for differential cross-sections,
response functions and A_TL asymmetry are discussed and compared to different
sets of experimental data for proton knockout from p_{1/2} and p_{3/2} shells
in 16O. We compare with a nonrelativistic approach to better identify
relativistic effects. The present relativistic approach is found to accommodate
most of the discrepancy between data from different groups, smoothing a long
standing controversy.Comment: 28 pages, 7 figures (eps). Major revision made. New figures added. To
be published in Phys. Rev.
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