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, $\vec d(\vec e, e'n)p$. We suggest to measure for this reaction, in the kinematics of quasi-elastic $en$-scattering, the ratio $R_{xz}=A_x/A_z$ of the asymmetries induced by the $x$- and $z$-components of the deuteron vector polarization. In the framework of the relativistic impulse approximation the ratio $R_{xz}$ is sensitive to $G_{En}$ in a wide interval of momentum transfer squared, whereas it depends weakly on the details of the $np$-interaction and on the choice of the deuteron wave function. Moreover, in the range $0.5\le Q^2\le$1.5 GeV$^2$, the ratio $R_{xz}$ shows a smooth dependence on $Q^2$, 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 e∓Ne^{\mp}N scattering, for axial parametrization of two-photon exchange

We analyze polarization phenomena for elastic lepton-nucleon scattering, parametrizing the $2\gamma$-exchange contribution, as the product of lepton and nucleon axial vector currents, that correspond to $C=+1$ 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 $G_E(Q^2)/G_M(Q^2)$ of nucleon electromagnetic form factors in model independent way, without any specific assumption about the $2\gamma$-exchange mechanism. Both these combinations have a general character and do not depend on the choice of the spin structure for the $2\gamma$-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 e+Ae+A-scattering. Part I: Virtual Compton Scattering

We calculate polarization phenomena for virtual Compton scattering on protons, at relatively large momentum transfer 1 GeV$^2$ $\le -q^2\le$ 5 GeV$^2$ on the basis of a model for $\gamma^*+ p\to \gamma+p$ with two main contributions: $\pi^0$-exchange in $t-$channel and $\Delta$-excitation in $s$-channel. This model applies from threshold to $\Delta$ region. The parameters entering in this model, such as coupling constants and electromagnetic form factors are well known. The analyzing powers for $\gamma^*+\vec p\to \gamma+ p$ and the components of the final proton polarization in $\gamma^*+ p\to \gamma+ \vec p$ are large in absolute value and show strong sensitivity to $\pi\bigotimes\Delta$ interference. These results can be applied to the calculation of radiative corrections to polarization phenomena in elastic $ep$-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, $\eta N$ -and $\omega N$ 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 $Q^2$ 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 $Q^2$-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 $\Lambda$ differs essentially from the value $\Lambda=0.1$ GeV, previously found using the dipole parametrization of the electromagnetic nucleon form factors $G_E$ and $G_M$. 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 $Q^2$=5-6 GeV$^2$ 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 $Q^2$=20-25 GeV$^2$. 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 $d +d \to n +{^3He}$, $d +{^3He} \to p +{^4He}$, $d +{^3H} \to n +{^4He}$, ${^3He} +{^3He}\to p+p +{^4He}$, ${^3H} +{^3He}\to d +{^4He}$, 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 $\vec d +\vec d \to n +{^3He}$ and $\vec d +\vec {^3H} \to n +{^4He}$.Comment: 33 pages 4 figure