Diffraction dissociation, an important background to photon-photon   collisions via heavy ion beams at LHC
  The cross sections for the production of hadrons in quasi-real photon-photon collisions in proton-proton and heavy ion interactions are compared with the corresponding cross sections for central diffraction and for photon-pomeron collisions. The signatures, heavy ions or protons with only slightly changed momenta together with two large rapidity gaps and a cluster of produced hadrons in the central region, are nearly identical in all three processes. Therefore, it will be rather difficult to distinguish the reactions experimentally. It is found, that central diffraction is the dominant process in collisions of protons, light and medium-heavy ions. The photon-pomeron and photon-photon processes have quite similar cross sections in collisions of heavy ions like lead. 
R.Engel (Univ. Leipzig and Univ. Siegen) M.A.Braun, C.Pajares and   J.Ranft (Univ. Santiago de Compostela)