Exclusive leptoproduction of $\rho^0$ mesons from hydrogen at intermediate virtual photon energies

Abstract. Measurements of the cross section for exclusive virtual-photoproduction of $\rho^0$ mesons from hydrogen are reported. The data were collected by the HERMES experiment using 27.5 GeV positrons incident on a hydrogen gas target in the HERA storage ring. The invariant mass W of the photon-nucleon system ranges from 4.0 to 6.0 GeV, while the negative squared four-momentum $Q^2$ of the virtual photon varies from 0.7 to 5.0 GeV$^2$. The present data together with most of the previous data in the intermediate W-domain are well described by a model that infers the W-dependence of the cross section from the dependence on the Bjorken scaling variable x of the unpolarized structure function for deep-inelastic scattering. In addition, a model calculation based on Off-Forward Parton Distributions gives a fairly good account of the longitudinal component of the $\rho^0$ production cross section for $Q^2>2$ GeV$^2$.