Impact parameter dependent S-matrix for dipole-proton scattering from diffractive meson electroproduction

We extract the S-matrix element for dipole-proton scattering using the data on diffractive electroproduction of vector mesons at HERA. By considering the full t dependence of this process we are able to reliably unfold the pr ofile of the S-matrix for impact parameter values b > 0.3 fm. We show that the I results depend only weakly on the choice of the form for the vector m eson wave function. We relate this result to the discussion about possible saturation effects at HERA. (C) 2001 Published by Elsevier Science B.V.