14 research outputs found
Experimental constraint on the meson form factors in the time--like region
The annihilation reaction is considered.
The constraint on time-like -meson form factors from the measurement done
by the BaBar collaboration at GeV is analyzed.Comment: 10 pages 3 figure
Two-component model for the axial form factor of the nucleon
The axial form factor of the nucleon is studied in a two-component model
consisting of a three-quark intrinsic structure surrounded by a meson cloud.
The experimental data in the space-like region are well reproduced with a
minimal number of parameters. The results are similar to those obtained from a
dipole fit up to 1 GeV, but they surprisingly show a zero between 2 and 3
GeV. Such behavior, predicted by the present model completely disagrees
with the dipole parametrization. The theoretical expression for the form factor
is then analytically extrapolated to the time-like region, giving the first
predictions in this regime. This kinematical region is especially interesting
for present and future colliders.Comment: 12 pages 2 figures Final version to appear in Phys. Rev.
Unitary and analytic model of nucleon EM structure, the puzzle with JLab proton polarization data and new insight into proton charge distribution
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 space-like region (obtained from process by the Rosenbluth technique) with recent Jefferson Lab data on
the ratio (measured in precise polarization
experiment) is suggested
to be solved in favour of the latter data which, however, unlike older data
cause an existence of the form factor zero, i.e. a difraction minimum in
around GeV. The new behaviour of
with the zero gives modified proton charge distribution with enlarged value of
the mean square charge radius.Comment: 9 pages, 11 eps figures. Talk presented at the workshop on Lepton
Scattering and the Structure of Hadrons and Nuclei, Erice (Italy), September
200
Two-component model for the deuteron electromagnetic structure
We suggest a simple phenomenological parametrization for all three deuteron
electromagnetic form factors, and show that a good fit on the available data,
with a minimal number of parameters, can be obtained. The present description
of the deuteron electromagnetic structure is based on two components with
different radii, one corresponding to two nucleons separated by 2 fm,
and a standard isoscalar contribution, saturated by and mesons,
only.Comment: 5 pages, 6 fig. 2 table
Study of resonant processes for multi-pion production in annihilation
In frame of a phenomenological approach based on Compton-like Feynman
amplitudes, we study multi-pion production in antiproton nucleon collisions.
The main interest of this reaction is related to the possibility to study the
properties of the presumable atom and of its resonances. For the
case of formation of a scalar or pseudoscalar resonant state, with
numerical results are obtained. The
differential cross section in an experimental set-up where the pions invariant
mass is measured, is given with explicit dependence on the lepton pair and
pions invariant mass.Comment: 9 pages, 4 figure
Phenomenological insight into JLab proton polarization data puzzle by deuteron impulse approximation
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.Comment: Revtex, 6 pages, 7 figure
Polarization effects in the reaction and determination of the meson form factors in the time--like region
The electron positron annihilation reaction into four pion production has
been studied, through the channel . 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 current. The elements of the
spin--density matrix of the meson were also calculated. Numerical
estimations have been done, with the help of phenomenological form factors
obtained in the space--like region of the momentum transfer squared and
analytically extended to the time-like region.Comment: 19 pages, 2 figures, to appear in Phys Rev
Cross section and polarization observables for the reaction
A model independent formalism for the electron positron annihilation reaction
has been derived. The differential and total cross
sections and the elements of the spin--density matrix of the -meson were
calculated in terms of the electromagnetic form factors of the corresponding
current. Simple models of form factors have been fitted
to the available cross section data and they allow to give numerical
predictions for the different observables.Comment: 19 pages, 6 figures Added formulas for axial meson decay in 3 pions
Modified version to appear in PR
Polarization effects in and determination of time like deuteron form factors
Polarization effects in the reaction have been
investigated for the case of longitudinally polarized electron beam and
arbitrary polarization of the produced deuteron, with the aim of a
determination of the time-like complex deuteron electromagnetic form factors.
General expressions of polarization observables are derived and numerical
estimations have been carried out by means of various models of deuteron
electromagnetic form factors, for kinematical conditions near threshold.Comment: 19 pages, 3 figure
Electromagnetic structure of vector mesons
Electromagnetic structure of the complete nonet of vector mesons (ρ0, ρ+, ρ−, ω, ϕ, K*0, K*+, K̄*0, K*−) is investigated in the framework of the Unitary and Analytic model and insufficient experimental information on it is discussed