Nuclear gamma -radiation as a signature of ultraperipheral ion collisions at the LHC

We study the peripheral ion collisions at LHC energies where a nucleus is excited to a discrete state and then emits gamma -rays. Large nuclear Lorenz factors allow the observation of high-energy photons up to a few tens GeV and in the angular region of a few hundred microradians from the beam direction. These photons can be used to tagg events with particle production in the central rapidity region in ultraperipheral collisions. To detect these photons it is necessary to have an electromagnetic detector in front of the zero- degree calorimeter in LHC experiments.