Ultra-peripheral heavy-ion collisions at the LHC

The LHC is not only the most powerful collider for proton–proton and heavy-ion collisions, but also for photon–photon and photon–hadron (γp and γPb) interactions, offering a unique opportunity to study fundamental aspects of QED and QCD via photon-induced processes. The protons and ions which are accelerated by the LHC themselves carry an electromagnetic field, which can be viewed as a source of photons.That is, a photon generated by one of these hadrons can interact with another photon (or with a hadron) producing a wide variety of particles.