Colour dipoles and the HERA data

Abstract

A very wide body of HERA diffractive electroproduction data is confronted with the predictions of the colour dipole model. In doing so we focus upon three different parameterisations of the dipole scattering cross-section, whose parameters are fixed by analysis of DIS structure function data. This analysis strongly suggests the presence of saturation effects, but is not definitive because the conclusion requires the inclusion of data at low-$Q^2$ values. Having fixed the parameters of the models from the DIS structure function data, the resulting dipole cross sections can be used to make genuine predictions for other reactions. Good agreement is obtained for all observables, as is illustrated here for deeply virtual Compton scattering(DVCS) and diffractive deep inelastic scattering(DDIS). There can be no doubting the success of the dipole scattering approach and more precise observations are needed in order to expose its limitations