  Through a determination of the $S$-matrix element for the scattering of a
localized colour dipole on a proton, we show that saturation effects can
already be sizable at HERA. The saturation scale is found to be around 1-1.5
$GeV^2$ for the highest available energies and for central collisions, and is a
decreasing function of the impact parameter.

High Energy Physics - Phenomenology