185 research outputs found
Precise method for the determination of the neutron electric form factor based on a relativistic analysis of the process $d(e,e'n)p
We generalize the recoil polarization method for the determination of the
proton form factor to the case of the disintegration of vector polarized
deuterons by longitudinally polarized electrons, . We
suggest to measure for this reaction, in the kinematics of quasi-elastic
-scattering, the ratio of the asymmetries induced by the
- and -components of the deuteron vector polarization. In the framework
of the relativistic impulse approximation the ratio is sensitive to
in a wide interval of momentum transfer squared, whereas it depends
weakly on the details of the -interaction and on the choice of the deuteron
wave function. Moreover, in the range 1.5 GeV, the ratio
shows a smooth dependence on , making the analysis simpler.Comment: 7 pages, 4 figs, 1 tabl
P-parity of charmed particles from associative photoproduction of D and D^*-mesons
We suggest to measure the triple polarization correlations in the exclusive
associative charm particle photoproduction, vector gamma + vector p --> vector
Lambda_c^{++} bar{D^0} with linearly polarized photons, as a method to
determine the P-parity of the charmed D-meson. The dependence of these
correlations on the parity P(N Lambda_c D) can be predicted in model
independent way. The t-dependence of the differential cross section for vector
meson photoproduction, gamma + p --> Lambda_c^{++} bar{D^{*0}}, in a model
based on D-exchange, is also sensitive to P(N Lambda_c D).Comment: 11 pages, 1 figur
Polarization phenomena in elastic scattering, for axial parametrization of two-photon exchange
We analyze polarization phenomena for elastic lepton-nucleon scattering,
parametrizing the -exchange contribution, as the product of lepton and
nucleon axial vector currents, that correspond to exchange in the
annihilation channel. We found two combinations of polarization observables
(one for three T-odd observables and another one - for five T-even
observables), which allow to measure the ratio of nucleon
electromagnetic form factors in model independent way, without any specific
assumption about the -exchange mechanism. Both these combinations have
a general character and do not depend on the choice of the spin structure for
the -exchange. We show the inconsistency of other approximations
recently used in the literature.Comment: Eight pages, no figure
Radiative corrections to polarization observables for elastic -scattering. Part I: Virtual Compton Scattering
We calculate polarization phenomena for virtual Compton scattering on
protons, at relatively large momentum transfer 1 GeV 5
GeV on the basis of a model for with two main
contributions: -exchange in channel and -excitation in
-channel. This model applies from threshold to region. The
parameters entering in this model, such as coupling constants and
electromagnetic form factors are well known. The analyzing powers for
and the components of the final proton
polarization in are large in absolute value and
show strong sensitivity to interference. These results
can be applied to the calculation of radiative corrections to polarization
phenomena in elastic -scattering.Comment: 18 pages, 9 figure
Model independent properties of two-photon exchange in elastic electron proton scattering
We derive from first principles, as the C-invariance of the electromagnetic
interaction and the crossing symmetry, the general properties of two-photon
exchange in electron-proton elastic scattering. We show that the presence of
this mechanism destroys the linearity of the Rosenbluth separation.Comment: 12 pages, no figures- Corrected misprints, changes in P. 7. No
changes in conclusion
Polarization Phenomena in Hadronic and Nuclear Processes in Threshold Regime
The threshold region for processes of hadronic and nuclear interactions is
very interesting for a theoretical as well as an experimental point of view. In
this region one can apply different physical methods, starting from classical
current algebra methods - for processes invloving soft pions, through effective
Lagrangian approaches - or perturbative chiral symmetry theory (ChPT). The
essential simplification of the spin structure of matrix elements for threshold
regime results in better understanding of the underlying mechanisms and allows
the analysis of polarization phenomena. A dedicated formalism is developed here
for a wide class of processes including even such complicated processes as
production of pseudoscalar and vector mesons in nucleon-nucleon collisions.
Many interesting physical problems are discussed: hidden strangeness of
nucleons and OZI-violation, -and interactions in S-state,
the determination of P-parity of strange particles. Special attention is
devoted to the analysis of the spin structure and polarization phenomena for
nuclear processes with light nuclei which have important applications in
fundamental astrophysics and in nuclear fusion.Comment: Review article, 83 pages 9 fig
Recent results on hadron form factors
We discuss the recent data on the electric proton form factor, obtained at
JLab, which show a spectacular deviation from the commonly assumed dipole
behavior. We discuss the implication of these results on the deuteron structure
and on the neutron electric form factor: at relatively large a revision
of the deuteron models may be required, and the neutron electric form factor
might become even larger than the proton electric form factor.Comment: 17 pages 4 figures Contribution to the Int. Workshop on Relativistic
Nuclear Physics from hundreds of MeV to TeV, Varna, Bulgaria, 10-16 September
2001. Replacement of Fig. 1 and relative tex
Sensitivity of pQCD deuteron structure to the nucleon form factors
We discuss the applicability of pQCD to the elastic scattering of electrons
on protons and deuterons. We analyze the -dependence of the reduced
deuteron form factor, taking into account the recent data on the electric
proton form factor and we find that the value of the QCD-scale parameter
differs essentially from the value GeV, previously
found using the dipole parametrization of the electromagnetic nucleon form
factors and . Moreover the predicted scaling behavior of the reduced
deuteron form factor can not be recovered in the Dirac and Pauli
representations for the nucleon electromagnetic form factors
QCD-view on hadron form factors in space-like and time-like momentum transfer regions
QCD gives definite predictions for hadron electromagnetic form factors in
space-like and time-like momentum transfer regions, such as the quark counting
rules, the hypothesis of hadron helicity conservation, and the relations
between nucleon and deuteron form factors in the formalism of reduced nuclear
matrix elements. Recent precise data about these form factors, obtained in
polarization experiments at the Jefferson Laboratory, have essentially changed
our view on this subject. QCD-predictions do not apply to these data up to
=5-6 GeV for deuteron and for the electric form factor of proton. An
analysis of these data suggests that the asymptotic region will more probably
start at =20-25 GeV. We show that the separation of magnetic and
electric proton form factors in the time-like region represents the most
stringent test of the asymptotic regime and QCD-predictions.Comment: 10 pages, 4 figures, Contribution to the 10th International
Conference on Nuclear Reacton Mechanisms, Varenna, Villa Monastero, Italy,
June 9-13, 200
Nuclear processes in magnetic fusion reactors with polarized fuel
We consider the processes , , , , , with particular attention for applications in fusion reactors. After
a model independent parametrization of the spin structure of the matrix
elements for these processes at thermal colliding energies, in terms of partial
amplitudes, we study polarization phenomena in the framework of a formalism of
helicity amplitudes. The strong angular dependence of the final nuclei and of
the polarization observables on the polarizations of the fuel components can be
helpful in the design of the reactor shielding, blanket arrangement etc..We
analyze also the angular dependence of the neutron polarization for the
processes and .Comment: 33 pages 4 figure
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