Pion Form Factor and Possible Heavy Vector Meson

Recently, various properties have been known about the iso-vector part of electromagnetic form factors; as to the momentum dependence it is generally accepted that the nucleon form factor behaves as a dipole, while that of a pion is nearly a simple pole with p-meson dominance.1> The momentum dependence of the nucleon form factors can most naturally be explained by an accurate evaluation of the uncorrelated two-pion contribution as well as the correlated part corresponding to the p meson.2>-4> The pion electromagnetic form factor Fn (t), which was taken as an input in the above-mentioned computations,2> •4> is expressed in terms of the I =J = 1 denominator function D 1 <1> as follows: Fn(t)=D 1<1l(O)/D 1<1>(t). (1) For the D-function in the small t region, iti<1(GeV/c)2, the p-wave solution of the N / D equation for pion-pion scattering is used.5> As is shown in Fig. 1, Eq. (1) leads us to the result that is very close to the single p-meson dominance; the form factor, thus obtained, agrees qualitatively with the recent experimental pion form factor.6> In order to discuss the nucleon form factor Yn the whole space-like range of existing data, it is necessary to take on the contribution from .,!t =1.3-1.7 and/or 2.4 GeV energy regions.4> In such a higher mass region we have no confirmation of a vector meson with 1°=1 + although there are several indirect experimental reports.7l