$γ$-Radiation of Excited Nuclear Discrete Levels in Peripheral

Abstract

A new process of a nuclear excitation to discrete states in peripheral heavy ion collisions is studied. High energy photons are emitted by the exited nuclei with energies up to a few tens GeV at angles of a few hundred microradians with respect to the beam direction. We show that a two stage process where an electron - positron pair is produced by virtual photons emitted by nuclei and the n the electron or positron excites the nucleus, has large cross section. It is equal to about 5 b f or CaCa collisions. On one hand it produces a significant $γ$-rays background in the nuclear f ragmentation region but on the other hand it could be used to monitoring the nuclear beam intensity at LHC. These secondary nuclear photons could be a good signal for triggering peripheral nuclear collisions.