541 research outputs found
Clustering aspects in nuclear structure functions
For understanding an anomalous nuclear effect experimentally observed for the
beryllium-9 nucleus at the Thomas Jefferson National Accelerator Facility
(JLab), clustering aspects are studied in structure functions of deep inelastic
lepton-nucleus scattering by using momentum distributions calculated in
antisymmetrized (or fermionic) molecular dynamics (AMD) and also in a simple
shell model for comparison. According to the AMD, the Be-9 nucleus consists of
two alpha-like clusters with a surrounding neutron. The clustering produces
high-momentum components in nuclear wave functions, which affects nuclear
modifications of the structure functions. We investigated whether clustering
features could appear in the structure function F_2 of Be-9 along with studies
for other light nuclei. We found that nuclear modifications of F_2 are similar
in both AMD and shell models within our simple convolution description although
there are slight differences in Be-9. It indicates that the anomalous Be-9
result should be explained by a different mechanism from the nuclear binding
and Fermi motion. If nuclear-modification slopes d(F_2^A/F_2^D)/dx are shown by
the maximum local densities, the Be-9 anomaly can be explained by the AMD
picture, namely by the clustering structure, whereas it certainly cannot be
described in the simple shell model. This fact suggests that the large nuclear
modification in Be-9 should be explained by large densities in the clusters.
For example, internal nucleon structure could be modified in the high-density
clusters. The clustering aspect of nuclear structure functions is an unexplored
topic which is interesting for future investigations.Comment: 11 pages, LaTeX, 10 eps files, Physical Review C in pres
Polarization Asymmetry In The Photodisintegration Of The Deuteron
The reaction Ā²(Ī³,p)n has been studied using a monochromatic and polarized gamma ray beam at energies E(Ī³)=19.8, 29.0, 38.6, and 60.8 MeV. The beam of an intensity ā¼4Ć10āµ Ī³/sec was obtained by Compton back scattering of mode-locked laser light off electron bunches in the Adone storage ring. Photoneutron yields were measured at nine neutron angles thetanā15, 30, 45, 60, 90, 120, 135, 150, and 165 deg in the center of mass (c.m.) for E(Ī³)=19.8, 29.0, and 38.6 MeV, and at thetanā30, 60, 90, 120, and 150 deg c.m. for E(Ī³)=60.8 MeV. The polarization independent component Iā(theta) of the differential cross section and the polarization dependent component PIā(theta) were deduced and the angular distribution of the azimuthal asymmetry factor Ī£(theta)=Iā(theta)/Iā(theta) was obtained. An extensive comparison with theory has been carried out and the inclusion of corrections due to meson exchange currents and to Ī-isobar configurations have been shown to be mandatory at energies E(Ī³)ā³40 MeV. Theoretical and experimental implications of intermediate energy deuteron photo- disintegration studies are discussed in some detail
Electron-induced proton knockout from neutron rich nuclei
We study the evolution of the \eep cross section on nuclei with increasing
asymmetry between the number of neutrons and protons. The calculations are done
within the framework of the nonrelativistic and relativistic distorted-wave
impulse approximation. In the nonrelativistic model phenomenological
Woods-Saxon and Hartree-Fock wave functions are used for the proton bound-state
wave functions, in the relativistic model the wave functions are solutions of
Dirac-Hartree equations. The models are first tested against experimental data
on Ca and Ca nuclei, and then they are applied to a set of
spherical calcium isotopes.Comment: 5 pages, 2 figures. contribution to the XIX International School on
Nuclear Physics, Neutron Physics and Applications, Varna (Bulgaria) September
19-25, 201
Nonlocal extension of the dispersive-optical-model to describe data below the Fermi energy
Present applications of the dispersive-optical-model analysis are restricted
by the use of a local but energy-dependent version of the generalized
Hartree-Fock potential. This restriction is lifted by the introduction of a
corresponding nonlocal potential without explicit energy dependence. Such a
strategy allows for a complete determination of the nucleon propagator below
the Fermi energy with access to the expectation value of one-body operators
(like the charge density), the one-body density matrix with associated natural
orbits, and complete spectral functions for removal strength. The present
formulation of the dispersive optical model (DOM) therefore allows the use of
elastic electron-scattering data in determining its parameters. Application to
Ca demonstrates that a fit to the charge radius leads to too much
charge near the origin using the conventional assumptions of the functional
form of the DOM. A corresponding incomplete description of high-momentum
components is identified, suggesting that the DOM formulation must be extended
in the future to accommodate such correlations properly. Unlike the local
version, the present nonlocal DOM limits the location of the deeply-bound hole
states to energies that are consistent with (\textit{e,e}\textit{p})
and (\textit{p,2p}) data.Comment: 14 pages, 10 figures, submitted to Physical Review
Nuclear transparencies for nucleons, knocked-out under various semi-inclusive conditions
Using hadron dynamics we calculate nuclear transparencies for protons,
knocked-out in high-, semi-inclusive reactions. Predicted transparencies
are, roughly half a standard deviation above the NE18 data. The latter contain
the effects of binned proton missing momenta and mass, and of finite detector
acceptances. In order to test sensitivity we compare computed transparencies
without restrictions and the same with maximal cuts for missing momenta and the
electron energy loss. We find hardly any variation, enabling a meaningful
comparison with data and predictions based on hadron dynamics. Should
discrepancies persist in high-statistics data, the above may with greater
confidence be attributed to exotic components in the description of the
outgoing proton.Comment: 13 pages + 3 figsin appended PS file, report # WIS-94/43/Oct-P
Radiative Corrections to Polarized Inelastic Scattering in Coincidence
The coplete analysis of the model-independent leading radiative corrections
to cross-section and polarization observables in semi-inclusive deep-inelastic
electron-nucleus scattering with detection of a proton and scattered electron
in coincidence has been performed. The basis of the calculations consists of
the Drell-Yan like representation in electrodynamics for both spin-independent
and spin-dependent parts of the cross-section in terms of the electron
structure functions. The applications to the polarization transfer effect from
longitudinally polarized electron beam to detected proton as well as to
scattering by the polarized target are considered.Comment: 18p, to be published in JET
Polarization asymmetry in the photodisintegration of the deuteron
The reaction Ā²(Ī³,p)n has been studied using a monochromatic and polarized gamma ray beam at energies E(Ī³)=19.8, 29.0, 38.6, and 60.8 MeV. The beam of an intensity ā¼4Ć10āµ Ī³/sec was obtained by Compton back scattering of mode-locked laser light off electron bunches in the Adone storage ring. Photoneutron yields were measured at nine neutron angles thetanā15, 30, 45, 60, 90, 120, 135, 150, and 165 deg in the center of mass (c.m.) for E(Ī³)=19.8, 29.0, and 38.6 MeV, and at thetanā30, 60, 90, 120, and 150 deg c.m. for E(Ī³)=60.8 MeV. The polarization independent component Iā(theta) of the differential cross section and the polarization dependent component PIā(theta) were deduced and the angular distribution of the azimuthal asymmetry factor Ī£(theta)=Iā(theta)/Iā(theta) was obtained. An extensive comparison with theory has been carried out and the inclusion of corrections due to meson exchange currents and to Ī-isobar configurations have been shown to be mandatory at energies E(Ī³)ā³40 MeV. Theoretical and experimental implications of intermediate energy deuteron photo- disintegration studies are discussed in some detail
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