Photons from spectators

Abstract

For Pb-Pb collisions at the LHC, the spectators, those parts of the Pb nuclei that are not involved in nucleon-nucleon collisions, continue on in the original beam direction, but they are not inert objects. If they are not too large a fraction of the original nucleus they are completely disintegrated into neutrons and protons. The spectators are subject to huge electric fields, fields causing accelerations so large that the quarks in the nucleons will radiate almost all of the energy they acquire from the field. Because of the extreme Lorentz transform most of the photons can be found in the 10 cm between the ingoing and outgoing beam pipes 140 m from the collision point. Spectator radiation may be the source of cosmic-ray photons seen in emulsion stacks at 100,000 ft.