C. Adamuščín

A unitary and analytic model of nucleon EM structure, the puzzle of JLab proton polarization data and new insight into the proton charge distribution

Abstract The unitary and analytic model of nucleon electromagnetic structure, describing all existing nucleon form factor data, is briefly reviewed. Then in the framework of this model the problem of inconsistency of older proton electric form factor data in a space-like region (obtained from the e − p → e − p process by the Rosenbluth technique) with recent Jefferson Lab data on the ratio G E p ( t ) / G M p ( t ) (measured in a precise polarization e − p → e − p experiment) is suggested to be solved in favor of the latter data which, however, unlike older data imply the existence of a form factor zero, i.e. a diffraction minimum in | G E p ( t ) | around t = − Q 2 = − 13 GeV 2 . The new behavior of G E p ( t ) with the zero gives a modified proton charge distribution with an enlarged value of the mean square charge radius.

Two-component model for the deuteron electromagnetic structure

We suggest a simple phenomenological parametrization for the deuteron electromagnetic structure, and show that a good fit on all available data for the three deuteron electromagnetic form factors (in the range Q{sup 2}{<=}2 GeV{sup 2}) can be obtained with a small number of parameters. The present description of the deuteron is based on two components with different radii, one corresponding to two nucleons separated by {approx_equal}2 fm, and a standard isoscalar contribution, saturated by {omega} and {phi} mesons, only.

Polarization effects in the reaction

The electron positron annihilation reaction into four-pion production has been studied, through the channel e(+)+e(-)-> (rho) over bar+rho. The differential (and total) cross sections and various polarization observables for this reaction have been calculated in terms of the electromagnetic form factors of the corresponding gamma(*)rho rho current. The elements of the spin-density matrix of the rho meson were also calculated. Numerical estimations have been done, with the help of phenomenological form factors obtained in the spacelike region of the momentum transfer squared and analytically extended to the timelike region.

e^++e^-\to \rho^+ +\rho^-

The annihilation reaction e + + e ! ¯ � + � is considered. The constraint on time-like �-meson form factors from the measurement done by the BaBar collaboration at p s = 10.5 GeV is analyzed.

and determination of the

The annihilation reaction e + + e ! ¯ � + � is considered. The constraint on time-like �-meson form factors from the measurement done by the BaBar collaboration at p s = 10.5 GeV is analyzed.

\rho -

The non-relativistic impulse approximation of deuteron electromagnetic form factors is used to investigate the space-like region behavior of the proton electric form factor in regard of the two contradictory experimental results extracted either from Rosenbluth separation method or from recoil proton JLab polarization data.

meson form factors in the time--like region

A model independent formalism for the electron positron annihilation reaction e{sup +}+e{sup -}{yields}a{sub 1}(1260)+{pi} has been derived. The differential and total cross sections and the elements of the spin-density matrix of the a{sub 1}-meson were calculated in terms of the electromagnetic form factors of the corresponding {gamma}*a{sub 1}{pi} current. Simple models of a{sub 1} form factors have been fitted to the available cross section data and they allow to give numerical predictions for the different observables.

Experimental constraint on the ρ meson form factors in the time-like region

The advanced

Experimental constraint on the

Unitary\&Analytic

\rho -

hyperon EM structure model has been constructed and behaviors of the