Michail P. Rekalo

Search for evidence of asymptotic regime of nucleon electromagnetic form factors from a compared analysis in space- and time-like regions

Abstract We compare the existing data about electromagnetic form factors of the proton in the time-like region of momentum transfer (up to s≃ 14 GeV2), with the corresponding data in the space-like region. From the constrains given by the Phragmen–Lindelof theorem, it turns out that the asymptotic regime can not be reached simultaneously for both form factors (electric and magnetic) in the considered region of momentum transfer. The angular dependence for the annihilation processes, such as p +p↔e + +e − , is sensitive to the asymptotic properties of form factors.

Considerations on rescattering effects for threshold photo- and electroproduction of π 0 on the deuteron

We show that for the S-state

The

{ensuremath{pi}}^{0}

\eta_c\gamma \gamma ^*

production in processes

transition form factor in the decay

ensuremath{gamma}+stackrel{ensuremath{rightarrow}}{d}d+{ensuremath{pi}}^{0}

\eta_c\to \gamma \ell^+\ell^-

and

and in the crossed channels

{e}^{ensuremath{-}}+stackrel{ensuremath{rightarrow}}{d}{e}^{ensuremath{-}}+d+{ensuremath{pi}}^{0}

\gamma e^-\to \eta_c e^-

the calculations of rescattering effects due to the transition

and

ensuremath{gamma}+stackrel{ensuremath{rightarrow}}{d}p+p+{ensuremath{pi}}^{ensuremath{-}}

e^+e^-\to\eta_c\gamma

(or