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

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 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

Polarization observables in the processes p+p→Θ++Σ+p+p\to \Theta^+ +\Sigma^+ and n+p→Θ++Λ0n+p\to \Theta^+ +\Lambda^0, for any spin and parity of the Θ+\Theta^+-hyperon in the threshold region

Using the symmetry properties of the strong interaction, such as the Pauli principle, the P-invariance, the conservation of the total angular momentum and isotopic invariance, we establish the spin structure of the threshold matrix elements for the processes $p+p\to \Theta^+ +\Sigma^+$ and $n+p\to \Theta^+ +\Lambda^0$, in a model independent way, which applies to any spin and parity of the $\Theta^+$-hyperon in the near threshold region. We predict the double spin observables for these processes, such as the dependence of the differential cross section on the polarizations of the colliding nucleons, and the coefficients of polarization transfer from a nucleon beam or target to the produced $\Sigma^+$ or $\Lambda^0$ hyperon. We prove that these observables are sensitive to the P-parity of the $\Theta^+$ baryon, for any value of its spin. As an example of dynamical considerations, we analyzed these reactions in the framework of K-meson exchange.Comment: 14 pages 1 figur

On radiative corrections for unpolarized electron proton elastic scattering

A statistical analysis of the elastic unpolarized electron proton scattering data shows that, at large momentum transfer, the size and the $\epsilon$ dependence of the radiative corrections, as traditionally calculated and applied, may induce large correlations of the parameters of the Rosenbluth fit, which prevent a correct extraction of the electric proton form factor. Using the electron QED structure (radiation) function approach the cross section of elastic electron-proton scattering in leading and next-to leading approximations is calculated and expressed as a correction to the Born cross section, which is different for the electric and the magnetic contribution. When properly applied to the data, it may give the solution to the problem of the discrepancy of the polarized and unpolarized results on electron proton scattering.Comment: 11 pagex, 5 figure

Relevant polarization observables for the study of the Roper resonance with hadronic probes

The purpose of this contribution is to stress the great importance of polarization observables for the study of nucleon resonances, in particular in the case of deuteron and proton probes. Polarization observables play a unique role in signing the reaction mechanism and bring new information in the microscopic description of baryon resonances. We will calculate the relevant polarization observables, for $p+d$- and $p+\alpha$-collisions, in case of inclusive reactions and for some selected exclusive channels

T-odd polarization observables in the photoproduction of charmed particles near threshold

The imaginary part of the matrix element for associative charm particle photoproduction, gamma+N-->Lambda(c)+(D) over bar, has a definite spin structure, near the reaction threshold, being characterized by a single parameter. This allows us to predict, in the framework of an effective Lagrangian approach, the energy and the angular dependence of T-odd polarization observables such as the analyzing power in the reaction gamma+(p) over bar-->Lambda(c) + (D) over bar and the polarization of the Lambda(c) hyperon, produced in the collision of unpolarized particles. We find sizable values for these observables, which can be measured experimentally

Scalar meson production in nucleon-nucleon collisions near threshold

We establish the model-independent spin structure of the matrix elements for the near-threshold scalar meson production in $pp-$ and $np$-collisions, when the final particles are emitted in S-state. Polarization phenomena are derived in a general form. The properties of the $t-$channel dynamics, which is based on different meson exchanges, are studied in terms of the $s-$channel parametrization of the matrix element. The prediction of a 'realistic' model, based on $\pi+\sigma$-exchanges are also presented.Comment: 16 pages 6 figure

Sensitivity of tensor analyzing power in the process d+p→d+Xd+p\to d+X to the longitudinal isoscalar form factor of the Roper resonance electroexcitation

The tensor analyzing power of the process $d + p \to d + X$, for forward deuteron scattering in the momentum interval 3.7 to 9 GeV/c, is studied in the framework of $\omega$ exchange in an algebraic collective model for the electroexcitation of nucleon resonances. We point out a special sensitivity of the tensor analyzing power to the isoscalar longitudinal form factor of the Roper resonance excitation. The main argument is that the $S_{11}(1535)$, $D_{13}(1520)$ and $S_{11}(1650)$ resonances have only isovector longitudinal form factors. It is the longitudinal form factor of the Roper excitation, which plays an important role in the $t-$dependence of the tensor analyzing power. We discuss possible evidence of swelling of hadrons with increasing excitation energy.Comment: 12 pages, 10 figure