Photon induced processes: from ultraperipheral to semicentral heavy ion collisions

We present an overview of processes induced by the coherent Weizsäcker-Williams (WW) photon cloud in heavy ion collisions. Due to the rather broad energy spectrum of photons a large variety of physics topics can be addressed. At the low-energy side, there are the electromagnetic dissociation processes. We discuss the few-neutron production via giant dipole resonance excitation. A typical high energy photonuclear process that has attracted much attention is the diffractive photoproduction of vector mesons. We review the color dipole approach to coherent and incoherent diffractive photoproduction of J / ψ mesons. Finally we turn to peripheral and semicentral collisions and discuss the role of WW photons in the production of very low- P T dileptons.