Vector resonances and electromagnetic nucleon structure.

Abstract

Motivated by new, precise magnetic proton form factor data in the timelike reigon, a hybrid vector meson dominance (hVMD) formalism is employed to investigate the significance of excited vector meson rsonances on electromagnetic nucleon structure. We find that the \ensuremath{\rho}(1700), \ensuremath{\omega}(1600), and two previously unobserved states are required to reproduce the local structure seen in the new LEAR data just above the pp\ifmmode\bar\else\textasciimacron\fi{} threshold. We also investigate sensitivity to the \ensuremath{\varphi} meson. The model dependence of our result is tested by introducing an alternative model which couples the isoscalar vector meson states to a hypothetical vector glueball resonance. We obtain nearly identical results from both models, except for ${\mathit{G}}_{\mathit{E}}^{\mathit{n}}$(${\mathit{q}}^{2}$) in the spacelike region which is very sensitive to the glueball mass and the effective \ensuremath{\varphi}NN coupling.