Gamma-radiation as a Signature of Ultra Peripheral Ion Collisions at LHC   energies
  We study the peripheral ion collisions at LHC energies in which a nucleus is excited to the discrete state and then emits $\gamma$-rays. Large nuclear Lorenz factor allows to observe the high energy photons up to a few ten GeV and in the region of angles of a few hundred micro-radians around the beam direction. These photons can be used for tagging the events with particle production in the central rapidity region in the ultra-peripheral collisions. For that it is necessary to have an electromagnetic detector in front of the zero degree calorimeter in the LHC experiments. 
Yu.V. Kharlov (Institute for High Energy Physics, Protvino, Russia),   V.L. Korotkikh (Scobeltsyn Institute of Nuclear Physi...