Exclusiveρ0,ω, andφelectroproduction

We have measured exclusive ${\rho }^0$, $\omega$, and $\phi$ meson electroproduction at the Cornell Wilson Synchrotron. The final ${\rho }^0$ data sample included 4637 four-constraint $e+p\to e+{\pi }^{+}+{\pi }^{-}+p$ events, with incident energy $E=11.5\mathrm{}$ GeV and electroproduction variables $Q^2$ and $W$ in the region $0.7<\mathrm{}{Q}^2<4\mathrm{}$ ${\mathrm{GeV}}^2$ and $1.9<W<\mathrm{}4\mathrm{}$ GeV. We find that the width of the forward ${\rho }^0$ diffraction peak increases rapidly as the lifetime of the intermediate hadron states decreases below $c\Delta \tau =1\mathrm{}$ fm and that the peak is wider for longitudinal ${\rho }^0$ than it is for transverse ${\rho }^0$. The longitudinal-transverse cross-section ratio $R_p=\frac{{\sigma }_L}{{\sigma }_T}$, obtained assuming $s$-channel helicity conservation, becomes constant at high $Q^2$. At fixed $W$ the diffractive vector-meson-dominance (VMD) model reproduces the $Q^2$ dependence of our cross section, $\sigma =({\sigma }_T+\epsilon {\sigma }_L)$, but is is not able to account for the rapid decrease in the cross section with increasing $W$ we observe. We find that $\frac{{\sigma }_{\omega }}{{\sigma }_{\rho }}$ depends on $W$ but is independent of $Q^2$ for $0.7<\mathrm{}{Q}^2<3\mathrm{}$ ${\mathrm{GeV}}^2$ and $2.2<W<\mathrm{}3.7\mathrm{}$ GeV. However, ${\sigma }_{\omega }$ is substantially larger than the diffractive VMD cross section. Our results for ${\sigma }_{\phi }$ are consistent with the $Q^2$ dependence of the diffractive VMD model for