Subnuclear fluctuations in vector meson photoproduction: a window to saturation

We present a model of coherent and incoherent photoproduction of vector mesons off proton and off nuclear targets. The computations are performed within the colour-dipole formalism. The targets are described by a profile, in the impact parameter space, including subnucleon degrees of freedom, so-called hot spots. Their positions change event by event. The key aspect of our model is that the number of hot spots grows with energy. We show that the measurement of dissociative production off protons at different energies offers new signatures of saturation. These measurements can be performed with current HERA and LHC data. The results presented here are based on our previous studies published in [1], [2] and [3].