COMMENT ON THE PREDICTION OF THE E+E--]NNBAR CROSS-SECTION TO BE REMARKABLY LARGER THAN THE E+E--]PPBAR

The former modified six-resonance VMD model with the correct analytic properties of nucleon electromagnetic form factors and the asymptotic behaviour predicted by the quark model for baryons is improved, first by an addition of the \gr\s`(2150) meson contribution, then taking masses and widths of all considered resonances to be fixed at the world-averaged values and finally, differing also the effective inelastic threshold of the isoscalar (isovector) Dirac nucleon form factor from the effective inelastic threshold of the isoscalar (isovector) Pauli nucleon form factor. By means of the resultant model the analysis of all existing spacelike region nucleon form factor data is repeated. In the timelike region just the attainable data on {Mathematical expression} cross-section are employed and the assumption currently used by experimentalists about the equality of electric and magnetic proton form factors close above the proton-antiproton threshold is tested in this manner. The prediction of the {Mathematical expression} cross-section to be remarkably larger than the {Mathematical expression} one is established again. © 1990 Società Italiana di Fisica.