Diffractive rho^0 photo- and leptoproduction at high energies

Abstract

We discuss the elastic photo- and leptoproduction of rho^0-mesons from nucleons at Q^2 < 1 GeV^2 as studied in recent experiments at HERA and FNAL. We find that the mass distribution of the measured π^+π^- pairs is determined to a large extent by the two-pion contribution to the photon spectral function as given by the pion form factor. With rising Q^2 the rate of diffractive events decreases and the π^+π^- mass distribution approaches a symmetric shape.

7 pages LaTeX, 3 figures, to appear in Phys.Lett.B