Measurement ofρoandφ-Meson Electroproduction

Abstract

We report measurements of ${\ensuremath{\rho}}^{0}$ and $\ensuremath{\varphi}$ 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 ${q}^{2}=\ensuremath{-}0.25 \mathrm{to} \ensuremath{-}2.0$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ and virtual-photoproduction center-of-mass energy squared $s=10 \mathrm{to} 30$ Ge${\mathrm{V}}^{2}$. As $|{q}^{2}|$ increases, the $\ensuremath{\rho}$ mass spectrum shape changes and the momentum-transfer distribution broadens. The ratio of the $\ensuremath{\rho}$ cross section to the total cross section decreases from 11% at ${q}^{2}=0$ to about 6% at $|{q}^{2}|={{m}_{\ensuremath{\rho}}}^{2}$. The ratio for the production of longitudinally to transversely polarized ${\ensuremath{\rho}}^{0}$ mesons is ${0.45}_{\ensuremath{-}0.10}^{+0.15}$ at $|{q}^{2}|={{m}_{\ensuremath{\rho}}}^{2}$, and the interference between longitudinal and transverse amplitudes is almost maximal. The relative $\ensuremath{\varphi}$-meson cross section also decreases as $|{q}^{2}|$ increases. Unitary lower bounds on the longitudinal-transverse ratio in inelastic electron scattering are derived.