330 research outputs found
Polarization transfer observables for quasielastic proton-nucleus scattering in terms of a complete Lorentz invariant representation of the NN scattering matrix
For the calculation of polarization transfer observables for quasielastic
scattering of protons on nuclei, a formalism in the context of the Relativistic
Plane Wave Impulse Approximation is developed, in which the interaction matrix
is expanded in terms of a complete set of 44 independent invariant amplitudes.
A boson-exchange model is used to predict the 39 amplitudes which were omitted
in the formerly used five-term parameterization(the SPVAT form) of the
nucleon-nucleon scattering matrix. Use of the complete set of amplitudes
eliminates the arbitrariness of the five-term representation.Comment: 29 pages, 2 figure
Form Factors from a Relativistic Dynamical Model of Pion Electroproduction
We obtain the electromagnetic form factors of the transition
by analyzing recent pion-electroproduction data using a fully relativistic
dynamical model. Special care is taken to satisfy Ward-Takahashi identities for
the Born term in the presence of form factors thereby allowing the use of
realistic electromagnetic form factors of the nucleon and pion. We parametrize
the dependence of the {\it bare} form factors by a
three-parameter form which is consistent with the asymptotic behavior inferred
from QCD. The parameters of the bare form factors are the
only free parameters of the model and are fitted to the differential
cross-section and multipole-analysis data up to (GeV/c) in the
-resonance region. This analysis emphasizes the significance of
the pion-cloud effects in the extraction of the resonance parameters.Comment: 9 pages, 5 figures, several small corrections, to be published in
Phys. Rev.
Off shell pi N amplitude and the p p->p p pi0 reaction
We have used a conventional model for the
reaction consisting of the Born term plus the -wave rescattering term. As a
novelty we have introduced the off shell dependence of the -wave
isoscalar amplitude. This amplitude is appreciably enhanced when one moves to
the off shell situations met in the problem and, as a consequence, the cross section becomes considerably larger than with the
use of the on shell amplitudes. Two different models for the off shell
extrapolation found in the literature have been used and the cross sections
obtained are large enough to account for the experimental data, although
uncertainties remain due to the incomplete knowledge of the off shell
extrapolation.Comment: 9 pages, LATEX version 3.14
The Axial Charge Renormalization in a Relativistic Description of Finite Nuclei
Starting from a realistic One-Boson-Exchange model of the nucleon nucleon interaction the relativistic mean field for nucleons is determined within the Dirac Brueckner Hartree Fock approach for finite nuclei. The matrix elements of the axial charge operator evaluated for the solutions of the Dirac equation with this selfenergy are investigated. These matrix elements are enhanced with respect to the equivalent non relativistic ones obtained from the solutions of the Schr\'odinger equation with the non relativistic equivalent potential. The present results confirm at a qualitative level the results for the axial charge renormalization obtained with perturbative approaches. However, the results obtained differ in size from those of the perturbative approach and are nucleus and state dependent
Deep Inelastic Lepton Scattering in Nuclei at x > 1 and the Nucleon Spectral Function
The nuclear structure function F_2A(x) has been studied in the Bjorken limit
for (l, l') scattering on nuclei in the region of x > 1 and was found to be
very sensitive to the information contained in the nucleon spectral function in
nuclei, particularly the correlations between momenta and energies in the
region of large momenta. Calculations were done in a local density
approximation using two different spectral functions for nuclear matter.
Results are compared to those obtained for a spectral function which has been
evaluated directly for the finite nucleus, ^{16}O, under consideration. For
values of x around 1.5 and larger the quasiparticle contribution is negligible,
thus stressing the sensitivity of the present reaction to the dynamical
properties of nuclei beyond the shell model approach. Several approximations
which are usually employed in studies of the EMC effect have been analyzed and
their inaccuracy in this region is demonstrated. The results stress the fact
that the nuclear structure function contains important information on nuclear
dynamical correlations. Therefore further measurements of F_2A(x) in that
region and for many nuclei would be most welcome.Comment: 24 pages, LaTeX, 11 PostScript figures, final version to appear in
Nuclear Physics
The Four-Boson System with Short-Range Interactions
We consider the non-relativistic four-boson system with short-range forces
and large scattering length in an effective quantum mechanics approach. We
construct the effective interaction potential at leading order in the large
scattering length and compute the four-body binding energies using the
Yakubovsky equations. Cutoff independence of the four-body binding energies
does not require the introduction of a four-body force. This suggests that two-
and three-body interactions are sufficient to renormalize the four-body system.
We apply the equations to 4He atoms and calculate the binding energy of the 4He
tetramer. We observe a correlation between the trimer and tetramer binding
energies similar to the Tjon line in nuclear physics. Over the range of binding
energies relevant to 4He atoms, the correlation is approximately linear.Comment: 23 pages, revtex4, 5 PS figures, discussion expanded, results
unchange
Relativistic quasipotential equations with u-channel exchange interactions
Various quasipotential two-body scattering equations are studied at the
one-loop level for the case of - and -channel exchange potentials. We
find that the quasipotential equations devised to satisfy the one-body limit
for the -channel exchange potential can be in large disagreement with the
field-theoretical prediction in the case of -channel exchange interactions.
Within the spectator model, the description of the -channel case improves if
another choice of the spectator particle is made. Since the appropriate choice
of the spectator depends strongly on the type of interaction used, one faces a
problem when both types of interaction are contained in the potential.
Equal-time formulations are presented, which, in the light-heavy particle
system corresponding to the mass situation of the system, approximate
in a reasonable way the field-theoretical result for both types of
interactions.Comment: Revtex, 20 pages, 12 PostScript figures, to appear in Phys. Rev.
Electromagnetic Scattering from Relativistic Bound States
The quasipotential formalism for elastic scattering from relativistic bound
states is formulated based on the instant constraint in the Breit frame. The
quasipotential electromagnetic current is derived from Mandelstam's five-point
kernel and obeys a two-body Ward identity. Breit-frame wave functions are
obtained directly by solving integral equations with nonzero total
three-momentum, thus accomplishing a dynamical boost. Calculations of
electron-deuteron elastic form factors illustrate the importance of the
dynamical boost versus kinematic boosts of the rest frame wave functions.Comment: RevTeX 3.0 manuscript, 9 pages. UU-file is a single PostScript file
of the manuscript including figures. U. MD PP #93-17
The coupled-channel analysis of the D and D_s mesons
The shift of the p-wave meson mass due to coupling to the DK channel is
calculated without fitting parameters using the chiral Lagrangian. As a result
the original mass 2.490 MeV generically calculated in the
relativistic quark models is shifted down to the experimental value 2317 MeV.
With the same Lagrangian the shift of the radial excited level is much
smaller, while the total width MeV and the width ratio is in
contradiction with the state observed by SELEX group.Comment: 9 pages, 2 figure
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