Hadronic physics in peripheral heavy ion collisions
  We discuss the production of hadronic resonances in very peripheral heavy ion collisions, where the ions collide with impact parameter larger than twice the nuclear radius and remain intact after the collision. We compare the resonance production through two-photon and double Pomeron exchange, showing that when we impose the condition for a peripheral interaction the $\gamma \gamma$ process dominates over the Pomeron interaction, due to the short range propagation of this last one. We also discuss the observation of light resonances through the subprocess $\gamma \gamma \to R \to \gamma \gamma $, which is a clean signal for glueball candidates as well as one way to check the existence of a possible scalar $\sigma$ meson. 
A. A. Natale