Exclusive Leptoproduction of rho^0 Mesons from Hydrogen at Intermediate Virtual Photon Energies

TL;DR

This paper reports measurements of the cross section for exclusive rho^0 meson production from hydrogen at intermediate energies, comparing results with models based on deep-inelastic scattering structure functions and Off-Forward Parton Distributions.

Contribution

It provides new experimental data on rho^0 meson production at intermediate energies and tests theoretical models involving structure functions and Off-Forward Parton Distributions.

Findings

Data agree with models based on deep-inelastic scattering x-dependence.

Off-Forward Parton Distributions model describes longitudinal cross section well for Q^2 > 2 GeV^2.

Results extend understanding of meson production mechanisms at intermediate 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 at W > 4 GeV 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.