Measurement of rho0 and phi-meson electroproduction

We report measurements of ρ⁰ and φ electroproduction at 19.5 GeV in a wide-aperture spectrometer which detected the scattered electron and the decay products of the vector mesons. Data are presented for the region of virtual-photon mass squared q²=-0.25 to -2.0 (GeV/c)² and virtual-photoproduction center-of-mass energy squared s=10 to 30 GeV². As |q²| increases, the ρ mass spectrum shape changes and the momentum-transfer distribution broadens. The ratio of the ρ cross section to the total cross section decreases from 11% at q²=0 to about 6% at $\left|q^2\right|={m_{\rho }}^2$. The ratio for the production of longitudinally to transversely polarized ρ⁰ mesons is ${0.45}_{-0.10}^{+0.15}$ at $\left|q^2\right|={m_{\rho }}^2$, and the interference between longitudinal and transverse amplitudes is almost maximal. The relative φ-meson cross section also decreases as |q²| increases. Unitary lower bounds on the longitudinal-transverse ratio in inelastic electron scattering are derived.